Kinkajou Power Supply
Design Report
December 18, 2003
Worcester Polytechnic Institute
Department of Electrical and Computer Engineering
EE2799 Team 8
RESPONSIBLE ENGINEERS
Emily Anesta, ECE Box 12
Takeshi Nosaka, ECE Box 261
Michael Sikorski, ECE Box 334
Table of Contents
1
2
Executive Summary ................................................................................................ 1
Understanding the Product Specifications .............................................................. 2
2.1
Introduction......................................................................................................... 2
2.2
Market Research ................................................................................................. 2
2.3
Customer Requirements...................................................................................... 7
2.4
Product Requirements......................................................................................... 8
2.5
Product Specifications ........................................................................................ 8
2.6
Conclusion .......................................................................................................... 9
3
Product Design Development ............................................................................... 10
3.1
Introduction....................................................................................................... 10
3.2
Value Analysis Criteria..................................................................................... 10
3.3
Design Options.................................................................................................. 11
3.4
Design Option Conclusions .............................................................................. 21
4
Architectural Description of Power Supply.......................................................... 22
4.2
Product Description by Module ........................................................................ 24
4.3
LED Driver ....................................................................................................... 24
4.4
Fan Driver ......................................................................................................... 29
4.5
Internal On/Off.................................................................................................. 31
4.6
Low Battery Protection and Indication ............................................................. 32
4.7
Circuit Protection .............................................................................................. 37
4.8
External On/Off Switch (User Interface).......................................................... 41
4.9
Complete Design............................................................................................... 42
5
Results................................................................................................................... 44
5.1
Design Issues .................................................................................................... 44
5.2
Meeting Requirements ...................................................................................... 44
5.3
Cost Analysis .................................................................................................... 47
5.4
Competitive Value Analysis ............................................................................. 48
5.5
Testing............................................................................................................... 51
6
Next Steps and Recommendations........................................................................ 52
7
References............................................................................................................. 53
Appendix A: Design Schedule.......................................................................................... 55
Appendix B: Value Ratings Explained ............................................................................. 56
Appendix C: Parts for Value Analysis Estimates ............................................................. 58
Appendix D: Competitive Value Analysis Table ............................................................. 60
Appendix E: Parts List for Prototype................................................................................ 61
Appendix F: Test Results.................................................................................................. 63
Appendix G: Prototype Photos ......................................................................................... 64
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Table of Figures
Figure 1: NorthStar Duel Flow Lantern.......................................................................................... 6
Figure 2: Schematic for LED driver ............................................................................................. 27
Figure 3: Schematic for fan driver ................................................................................................ 30
Figure 4: Schematic for battery protection ................................................................................... 35
Figure 5: High voltage protection schematic ................................................................................ 40
Figure 6: Reverse polarity protection schematic .......................................................................... 40
Figure 7: Schematic for circuit protection .................................................................................... 41
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Table of Tables
Table 1: Weighted Value Criteria ................................................................................................. 10
Table 2: Relationship between VIN and protection LED .............................................................. 33
Table 3: Relationship between VIN and internal switch................................................................ 34
Table 4: Cost Analysis of Voltage Regulator and Reference ....................................................... 36
Table 5: Low Battery Protection/Indication Performance with 5% resistors (V= 5V +/-2%) ..... 36
Table 6: Low Battery Protection/Indication Performance with 1% resistors (V= 5V +/-2%) ..... 36
Table 7: Cost of 1% and 5% Resistors.......................................................................................... 37
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1 Executive Summary
This document details a power supply design for the Kinkajou projector, a product
designed by non-profit organization Design That Matters. The Kinkajou contains a 5W LED and
a cooling fan that need to be powered by a 12V lead-acid car battery. Design That Matters plans
to use the Kinkajou for literacy classes in Mali, but this market may be expanded to other parts
of Africa and other types of applications.
Based on our understanding of the needs and priorities of the client, Design That Matters,
and our research of the market in Mali, we composed customer and product requirements
emphasizing low-cost, high performance, durability and efficiency. Based on our testing to-date,
we anticipate that our product will meet these requirements, and we have recommended more
thorough testing and some possible design modifications to make the product even better. We
also acknowledge that there are still more trade-offs that can be made. Our current product
components achieve the low cost of $6, but could be made cheaper by sacrificing some
performance. Also, performance could be enhanced if the client were willing to increase the
cost.
1
2 Understanding the Product Specifications
2.1 Introduction
Our market research drove the customer specifications from which we derived our product
specifications. We have focused on providing the product that best meets the needs of Design
That Matters, with applications to other markets, such as camping, considered secondary.
However, we would like to acknowledge that a substantial commercial market for the product
would help to reduce the manufacturing costs per product which could help this product be more
affordable to the market in Mali.
2.2 Market Research
For our market research we looked specifically at the Kinkajou for use in adult literacy
classes in Mali. We also investigated other potential markets for the product and potential
competitors. Research was conducted by talking directly with experts from the markets and
through targeted web searches.
2.2.1 Kinkajou in Mali
2.2.1.1 Identifying the Market
Design That Matters (DTM) is a non-profit organization that has designed the Kinkajou
LED Projector as a tool for teachers of adult literacy in Mali, Africa. This is our primary client
for this product, and is the most important aspect of our market research.
Most of the information about the market for applying our power supply to the Kinkajou
for adult literacy classes in Mali came from DTM directly. When they came and spoke to us on
Wednesday, October 29th 2003, they gave us a lot of information about their needs for this power
supply. Since DTM has extensive experience with the market in Mali, we were able to glean
most of the important information directly from them. In addition, we browsed the World Wide
Web about the climate, language, and people of Mali.
2.2.1.2 Results
The functionality of the product was our first consideration. According to DTM, the
device is intended to drive a 5W LED Microfilm Projector, protect the LED, and run a DC
cooling fan all from a 12V lead-acid car battery. The LED needs to be run at a strong and
constant brightness for the duration of product use. DTM indicated that one of the problems
with the current driver circuit is that the LED intensity changes in step intervals over time. They
indicated that this may be related to temperature. DTM also indicated that they would like the
2
device to work when a battery charger is hooked up to the battery which is supplying power to
the device.
Cost is a huge factor for the market in Mali. DTM explained to us that the cost for our
portion of the design has not been fixed, but ultimately should be as low as possible. According
to our engineering managers, this should not add more than 10% to the production cost, (Vaz
2003). According to DTM, they aim for a production cost for the Kinkajou of about $50. Also
related to cost is the protected sales volume. According to DTM, at least 800 units would be
produced just for the World Education literacy course, but there is potentially a much wider
market including other types of training classes. In order to help grow sales other markets could
also be explored. According to DTM the Kinkajou, and thus our driver circuit, could be used for
technical training classes in Mali as well as literacy classes in Benin.
How frequently the device will be in operation was another important consideration.
Based on the scenario given by DTM, a teacher will use the projector at night, charge it during
the day, then using it again the following night. DTM also indicated that the literacy classes are
typically 2-3 hours long. “The circuit must be as efficient as possible to extend battery life. In
addition, the circuit should indicate when battery voltage is low and shut itself down if the
voltage drops below a certain level,” (Vaz 2003). We can assume that the device will be
operated by teachers or their assistants in Mali, based on the scenario provided by DTM.
Size may seem unimportant at this time, however this type of information is important
even now. According to DTM, the power supply should be small enough to eventually integrate
into the device. The current drive circuitry as shown to us by DTM is about the size of a hockeypuck.
The country of manufacture plays a role in requirement generation on this project. DTM
indicated that the product may initially be manufactured in Asia with an aim to move
manufacturing, or at least assembly to Mali. Related to manufacture is life expectancy of the
product. According to DTM, the most important thing to worry about is the Mean Time Before
Repair, not the Mean Time Before Failure. Given that, the product should last as long as
possible before any repairs are needed. DTM indicated that the devices should be able to be
easily repaired by local Mali technicians. According to DTM, someone who repairs this device
may not have access to such tools as the proper screwdriver or a voltmeter.
In addition to that which we learned from DTM, there are a number of implicit
requirements which we need to asses. Although not directly stated, it is clear the circuit should
not electrocute the user or cause harm in any other way. Operating conditions need big
consideration from early on. In Mali we can plan for our driver circuitry to operate between an
average minimum temperature of 11ºC and an average maximum temperature of 42ºC
(Geography IQ 2003). Humidity averages are from a low of 28.3% to a high of 80.5% (United
Nations Environment Programme 2003).
3
2.2.1.3 More about Mali
As reflected in the answers above, the device will be operated, repaired, and possibly
manufactured by people in Mali. The population of Mali is 11,626,219 and 49.8% of those are
between the ages of 15 and 64. French is Mali’s official language, and the GDP per capita
purchasing power parity is $860. Mali is one of the poorest countries in the world and 64% of
it’s citizens live below the poverty line. Electricity production is 480.2 million kWh. There are
45,000 phone lines and 40,000 mobile phones. 30,000 people have access to the internet.
(Central Intelligence Agency 2003)
There is varying information about the rate of literacy in Mali. The CIA states literacy
rates of 46.4% of the total population, 53.5% of males and 39.6% of females, (Central
Intelligence Agency 2003). The World Bank Group puts the statistics in terms of illiteracy, and
estimates the rates at 72.8% of the total population and 82.7% of females, (The World Bank
Group 2003). According to the United Nations, Mali has the third highest number of illiterate
men (64.2%) and the third highest number of illiterate women (84%).
2.2.1.4 Conclusion
From this research, one can see that economics is our overriding consideration. The
market has a low income with which to purchase this product and little access to technical
resources, (tools and information sources such as the internet), to assist them in operating or
repairing this product. The device will be used daily for 2-3 hour increments in a humid
environment. Mean time before repair is an important indicator of product quality to this market.
In order to surpass the current LED driver circuit for Kinkajou we need to provide a consistent
power source for the duration of usage.
2.2.2 Additional Markets
2.2.2.1 Identifying the Market
One of the other possible markets for a 5 Watt LED power source is the outdoor sporting
goods industry. It may be possible that the power source could be readily adapted for use with a
5 Watt LED powered lantern or other lighting device. Lighting products represent a large
portion of the goods produced by camping and adventure gear manufacturers such as Coleman
and General Electric according to Debbie, an outdoor gear expert at Eastern Mountain Sports in
Worcester Massachusetts. Outdoor manufacturers market to several smaller markets including:
day hikers, backpackers, campers, and paddlers, among others.
We spent a significant amount of time examining the products that currently in the
market place. By understanding what products are currently available, and the specifications of
each of these products, we hoped to understand what characteristics of a power supply would be
desirable to the lighting manufacturers.
4
2.2.2.2 Results
In order to further understand the needs of the market, the research team turned to
Debbie, an outdoor gear expert at Eastern Mountain Sports in Worcester Massachusetts. As an
outdoor products sales associate, as well as an avid camper, Debbie understands the needs of this
market. Her statements provided valuable information about the outdoor adventure industry and
its lighting requirements.
Debbie explained that the environment for these products is harsh. Wind, water, glaring
sun and freezing temperatures are all possible. Based upon her response we reasoned that the
product would have a tough existence. We then inquired about the life expectancy of products
that are currently on the market and what se would like to see from our device to make it viable.
Debbie explained that the product should last as long as possible. It should be able to endure a
minimum of three or four seasons before needing replacement.
In many cases Debbie told us that our product should be as close to the current products
and beat them whenever possible. This was the case for product cost, run time, weight, low
battery warning and overall product appearance. When questioned about the negative aspects of
products currently on the market she mentioned that liquid fuel lanterns are messy and dangerous
while electric lanterns typically have poor light output. Debbie explained that long run time and
bright light output are the most important features to consider. Se also mentioned that some
areas of the outdoor industry have very specific needs. For example the backpacking industry
demands small, lightweight products above all else.
Conversing with Debbie about the outdoor adventure lighting market revealed important
initial information. Currently, electric lighting is growing in popularity as an alternative to
kerosene, gasoline, or propane powered lighting sources. Electric lighting eliminates the dangers
these combustible fuels pose. On the market today there exist three forms of lighting for use in
the outdoor sporting goods industry. The traditional lighting source has been incandescent bulbs
in flashlights and small lanterns. This source puts out a good amount of light, however it wastes
a lot of battery power in the form of heat and are not as durable as a solid-state light source such
as an LED. Fluorescent tubes, while more efficient, have poorer light output than incandescent
bulbs and are typically large. More recently, LED technology has been used for lighting. The
huge advantage of this design is the efficiency. The light source has reduced dramatically in
both size and weight, though the light output of products currently on the market is poor.
As Debbie explains, liquid fuel, LED, fluorescent as well as incandescent lighting
techniques are currently utilized in the industry. Each has found its own niche. Conventional as
well as fluorescent lanterns are popular with campers. Here weight and size are not as important
light output and runtime. Examples of lanterns can be found in Figure 1 and Figure 2.
Backpackers prefer the light weight and small size of the LED designs. For situations that
require more lighting power, conventional incandescent bulbs fill that requirement. Paddlers
seem to agree with the backpackers and utilize similar products.
5
Model No. 2000A750
Model No. 5348H701
• Can run 6-8 hours without fuel refill
• Powered by 8 D-cell batteries
• Lantern runs up to 25 hours on a single
set of batteries
Figure 1: NorthStar Duel Flow Lantern
Figure 2: 2-Tube Rechargeable Lantern
(Coleman 2002)
For pricing information we examined the products available at one local retailer, Eastern
Mountain Sports. Price varies greatly depending upon the product characteristics. On the low
end flashlights start from less that $5 and go up to nearly $40. Liquid fuel lanterns start at $40
and range to about $110. Electric lanterns range from $15 to $45. Headlamps often include
LED and incandescent bulbs within the same housing. These range from $20 to $75.
The market for lanterns is a huge one. A sense for the market size can be had by
examining the size of camping organizations. The Good Sam Club, for example, is the largest
recreational vehicle association in America. The organization numbers over one million
households. (Good Sam Club 2003)
2.2.2.3 Conclusion
From the market research it is clear that there is an additional market for a bright, long
lasting light source such as the one our power supply could provide. It has become apparent that
the outdoor adventure market is always looking to the latest technology to solve its lighting
problems. It is also apparent that the size and weight requirements of the backpackers and
paddlers may render our power supply impractical. The more likely market for this product
would be camping lanterns. In this case size and weight are not the inhibiting factors they are in
other cases. The number of products sold in this industry has the potential to be very large. If
only one percent of the households within the Good Sam Club purchased our camping lantern it
would drive sales to exceed 10,000 units. This market is certainly an applicable market for our
product.
6
2.3 Customer Requirements
We used the data gathered from our market research to assess the requirements of our
customer. First, we analyzed data from the research about our primary market, the Kinkajou for
use in Mali. Then, we analyzed market research about other possible markets for our product to
see how similar the requirements were.
2.3.1 Kinkajou in Mali
We used information from Design That Matters and our own research to assess the needs
of the customers of the Kinkajou in Mali.
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•
Inexpensive
Function in Mali’s climate
Last as long as possible before repairs needed
Take up very little space so as to be easily incorporated inside device
Be able to run for at least 3 hours before recharging
Warn the user before shutting down when battery gets too low
Be able to run LED at a consistent (strong) brightness for the duration of time in use
Run the fan enough to keep system cool
Protect the battery from damage
Easy to repair
Easy to operate
Safe
2.3.2 Outdoor Adventure Market
After learning about this segment of the market from researching products currently
available and speaking with an expert in the industry, we compiled this list of the consumer’s
requirements for the power supply to camping lighting products.
•
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•
•
•
•
durable (long life span)
waterproof (it will get wet)
bright (it needs to light up a broad area/ brightness comparable to liquid fuel)
battery run time (it should last at least as long as current liquid fuel lanterns)
portable (reasonable dimensions)
lightweight (its weight must be within the range of current products)
2.3.3 Conclusion
The requirements for the camping market overlap those of the Kinkajou market in most
respects. The camping market also desires a waterproof product, but the power supply we would
create would be integrated within the packaging of some lighting product, which could be
waterproof.
7
Our analysis is that by designing to meet the more stringent requirements of the Kinkajou
application for this power supply, we can create a product that will be viable in both markets.
An advantage of expanding the market beyond the Kinkajou, is that higher quantity will drive
down the cost of production helping us to meet an important requirement of affordability.
2.4 Product Requirements
We used the Kinkajou customer requirements to compose a set of product requirements
to drive the design of our power supply. The Kinkajou customer requirements include all of the
outdoor adventure market requirements and some others, so this set of product requirements will
meet the needs of both markets.
2.4.1 List of Requirements
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Inexpensive
Durable
Function in Mali climate
Allow user to easily turn on and off the power supply
Use readily available components
Warn user when battery becomes low
Protect battery
Provide steady current/voltage output, even as temperature changes
Provide some casing to protect it until integrated into device
Make compact so as to be easily incorporated inside device
Use power as efficiently as possible to minimize recharging
Minimum must be able to run steadily for 3 hours
Run the fan as necessary to keep device cool.
Do not have exposed wires or other safety hazards
Circuitry should be able to handle a lot of jostling and generally harsh treatment, so as to
last when being transported around and used repeatedly
Graphical instructions/labels where possible, French instructions/labels where necessary
2.5 Product Specifications
In order to determine the product specifications, we had to research the input and output
devices for which we are designing. According to Design That Matters the Kinkajou LED is a
Luxeon 5W white LED, (Vaz 2003). This LED has a typical current of 700mA and voltage of
6.84V with a very steep current-voltage relationship, (Lumileds 2002). The steep currentvoltage relationship indicates that we should attempt to control the current of the LED since
there is a wider range of acceptable currents than there is of acceptable voltages. The Kinkajou
cooling fan is a 12Vs 100mA fan, (Vaz 2003).
A car battery, though nominally 12V, can have a range of potentials. The minimum
voltage of a car battery, below which the battery will be depleted to the point of damage, is
10.5V, (Panasonic 2000). For a high voltage, we consulted with WPI project teams working on
8
battery charger devices. We determined that if the battery charger is hooked up to the device, we
needed to accommodate the maximum potential applied to the battery and therefore to our power
supply. According to the teams with whom we spoke, this maximum was 16V. This exceeds the
maximum potential we would expect from the battery alone and so should be a safe maximum to
use, (Panasonic 2000).
2.5.1 List of Specifications
•
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•
•
•
•
•
•
•
•
•
•
•
•
•
Accept 12V Lead-Acid Car battery input (10.5-16V)
Provide consistent DC current of 700mA to LED for a minimum of 3 hours
Provide 110mA DC at 12V to fan
Turn off automatically before battery is run beyond rechargeability (10.5V)
Provide warning output to the user before shut-off occurs
Minimize power consumption
On/off switch
Function in humidity and temperature of Mali:
Temperature 11ºC - 42ºC
Humidity 28.3% - 80.5%
Have casing to protect device from humidity and dust (until it is incorporated into the
Kinkajou package)
Use inexpensive, readily available, durable components and casing
Use a minimum number of parts
Connections within driver circuit should be durable
Connections to input and output should be durable
Should not weigh more than 1lb. (lighter is better)
Should not take up more than 1,000 cm3 (smaller is better)
Graphical or French labels for on/off and low battery indicator
2.6 Conclusion
Our research has shown that there is a market for our power supply. Certainly there is the
Kinkajou projector application, and it is quite feasible that our product could be used in other
applications such as camping lanterns. The most important customer requirement is price. This
will most likely be the most difficult requirement to meet. However the additional markets of
the product will allow us to reduce the cost by increasing the volume of power supplies sold.
The power supplies currently on the market do not fit the specific needs of these applications.
The specifications of our product are tailored to the needs of this market and establish it as the
perfect fit for these applications. We conclude that our product is a wise investment.
9
3 Product Design Development
3.1 Introduction
Based on the customer and product requirements, we assessed some possible design
approaches for the various portions of our design. Once these design decisions were made, we
compared our design approaches against our potential competitors, weighing the value criteria of
each. For design decisions and our competitive analysis, we used value matrices as our primary
analysis tool. We would like to acknowledge that the scores generated by this kind of system are
fairly artificial and imprecise, however they can be helpful to generally analyze desirability of
the options.
3.2 Value Analysis Criteria
For design options and competitive analysis, we composed a set of value criteria. We
created the criteria and weightings based on the market research and specifications described in
section 2 of this report. We then used the equation Quality*Convenience/Cost to score each
option.
We weighted each value criteria on a 100 point scale as follows:
Weighting Factor
100
80
75
75
60
40
25
10
10
Criterion
Cost
Feasibility of Implementation
Durability
Longevity
Efficiency
Performance
Usability
Serviceability
Size
Table 1: Weighted Value Criteria
We determined cost to be the most important factor since this product will be used for the
Kinkajou Projector, a device intended to facilitate literacy classes in Mali. Feasibility of
implementation scored high on this scale, since we have a limited time frame and need to stick to
designs that we are capable of successfully completing. Durability/longevity has ¾ the
weighting of cost since repairs and access to technical tools is an issue in Mali. Efficiency is
also important, but since the projector will probably be charged after each 3 hour class, a durable
and low-cost product does outweigh efficiency. Performance rates less than half of cost since the
users in Mali cannot afford to pay more or sacrifice cost, durability and longevity for a higher
performance product. Usability and size rate the lowest. These would be nice, but to some
10
extent can be sacrificed for lower cost and more durability and longevity. See “Value Ratings
Explained” in Appendix B for details on how the ratings are determined for each category.
3.3 Design Options
We examined a number of design options for each system involved in the product. The
design decisions we had to make were:
•
•
•
•
•
What type of approach (digital/discrete analog/integrated circuits) should we take for the
overall DC-DC conversion?
What strategy should we take when designing an efficient and effective LED driver?
What strategy should we take when designing an efficient and effective fan driver?
What interface should we use to indicate a low battery to the user?
What method should we use to protect the battery from excessive voltage and/or
excessive current conditions?
Each of these design questions had a number of choices which we had to weigh against
our value criteria. We carefully selected appropriate criteria and ratings for each design option
and used a value matrix to compare them.
3.3.1 Current Regulation Circuitry (LED Driver)
We analyzed three main options for the LED driver circuitry. We analyzed cost,
feasibility of implementation and performance for this design decision. We determined that
usability was not a factor in the decision. None of the options require any user input within the
LED driver circuitry itself. Therefore usability was not relevant to the decision.
3.3.1.1 Option 1: Digital Controller (PIC)
Digital controllers would provide constant current, but have a high cost. Note that cost here does
not include components that are peripheral to the PIC.
Criterion
Cost
Feasibility of
Implementation
Performance
Score
2.05
2
4
E.g. PIC12C671 (Microchip 2003)
Our team has some of the necessary background for this.
This would do well to provide the LED with the constant
current it requires.
3.3.1.2 Option 2: DC-DC Integrated Circuit
For this option, we investigated robust ICs that could perform the entire conversion. Note that
cost here does not include components that are peripheral to the IC.
Criterion
Cost
Feasibility of
Implementation
Score
3.50
4
E.g. AA9090A (Jameco 2003)
Our team has the ability to implement this easily.
11
Performance
2
Most of the products on the market do not seem to exactly
meet our needs.
3.3.1.3 Option 3: Discrete Analog Components and IC Combination
An IC could be combined with discrete components using a design such as a Buck converter.
Criterion
Cost
Score
1.50
Feasibility of
Implementation
Performance
4
E.g. Estimated cost of an appropriate IC and basic discrete
components. (Jameco 2003), (Mouser 2003).
Our team has most of the background needed to
implement this design.
This affords flexibility to make changes to the discrete
circuitry while giving us the robustness of available ICs.
5
3.3.1.4 Comparison Value Matrix
Value Analysis
Market DC-DC IC
Convenience
1 Performance
2 Feasibility of Implementation
Value point
Value point
40
80
2
4
Digital (PIC)
Total
80
320
400
Total
Market DC-DC IC
Cost
1 Initial Cost
Value point
Value point
100
3.5
Value point
4
2
IC plus Discete
Total
160
160
320
Digital (PIC)
Total
350
350
Total
1.1
Customer Value: (Quality*Convenience/Cost)
Value point
2.05
Value point
5
4
Total
200
320
520
IC plus Discete
Total
205
205
1.6
Value point
1.5
Total
150
150
3.5
3.3.1.5 Conclusion
From the comparison value matrix it seems that a combination of integrated
circuits and discrete analog components will be our best choice to maintain the constant current
that is required by our LED. Our research indicates that an integrated circuit for the entire LED
driver would be expensive and may not meet our exact needs. Not quantified in our value matrix
is the qualitative observation that modifications to the design might be too constrained by the
specifications of the selected IC. A digital approach, such as a PIC microcontroller, seemed to
add more complexity than necessary without a significant savings in cost or improvement in
performance.
3.3.2 LED Driver Strategy
We analyzed three main options for the LED circuitry. After brainstorming and research,
we decided to investigate three options for the LED driver strategy: running LED at constant
current, pulsing LED, and running LED at reduced power. We analyzed cost, feasibility of
implementation, longevity, efficiency, performance and usability for this design decision.
12
For the LED Driver we decided to weight the performance more heavily, at 80. We
determined that performance, for this piece, weighed as heavily as feasibility of design. We also
gave each item the same cost rating of 0.50. At this stage of decision-making, we did not know
what the cost of each of these strategies would be, and were more interested in assessing
performance and efficiency.
3.3.2.1 Option 1: Run LED at Constant Current
Criterion
Feasibility of
Implementation
Longevity
Efficiency
Performance
Usability
Score
4
We know how to build this type of circuit.
4
3
5
5
This would minimally tax the circuitry; we expect it to last.
This is not particularly efficient.
This would run the LED at a good brightness.
This would require no input from the user.
3.3.2.2 Option 2: Pulse LED
Criterion
Feasibility of
Implementation
Longevity
Efficiency
Performance
Usability
Score
3
3
5
5
5
This uses known designs for Pulse Width Modulation,
(PWM).
The pulsing of this circuit gives it more potential to break.
We could save a lot of power using PWM.
This would run the LED at a good brightness.
This would require no input from the user.
Consulted U.S. Patent 4,866,430 (USPTO 2003)
3.3.2.3 Option 3: Run LED at Reduced Power
Criterion
Feasibility of
Implementation
Longevity
Efficiency
Performance
Usability
Score
4
We know how to build this type of circuit.
4
4
2
5
This would minimally tax the circuitry; we expect it to last.
This saves some energy.
This would run the LED at a poor brightness.
This would require no input from the user.
13
3.3.2.4 Comparison Value Matrix
LED Driver
Value Analysis
Market Constant Current
Quality
1 Efficiency
2 Performance (LED constant brightness)
3 Longevity
Value point
60
80
75
Pulse LED
Total Value point
Value point
3
5
4
180
400
300
880
Total
Market Constant Current
Convenience
1 Usability
2 Feasibility of Implementation
Value point
Value point
25
80
5
4
125
320
445
Market Constant Current
Cost
1 Initial Cost
Value point
Value point
100
0.5
Total
Value point
5
4
50
50
Value point
0.5
Value point
4
1
4
125
320
445
Value point
5
4
240
80
300
620
Total
125
320
445
Reduced Power
Total
50
50
Value point
0.5
8232.5
3.3.2.5 Conclusions
Pulsing the LED, utilizing pulse-width modulation, provides to be the most efficient and
the best performing of the three design options. Although the constant current option comes
fairly close, the pulsing option stands out as the very desirable. We decided to actually combine
these approaches by pulsing the power drawn from the source while running the LED at a
constant current. See section 4.2.1 for details on this strategy.
3.3.3 Fan Driver Strategy
We analyzed five main options for the fan driver circuitry: running a fan at constant fullspeed, running the fan at low speed, running the fan intermittently, adding a manually controlled
on/off switch, and using a temperature-controlled fan. Cost, feasibility of implementation,
longevity, efficiency, performance and usability were the categories of analysis for this design
decision.
For the Fan Driver we decided to weight the performance more heavily, at 100. We
determined that performance for this particular component is crucial since the consequence of
poor performance would be a meltdown of the product or damage to the projector LED.
14
Total
Reduced Power
Total
Pulse LED
Total
7832
Customer Value: (Quality*Convenience/Cost)
300
400
225
925
Pulse LED
Total
Total
5
5
3
Reduced Power
Total
Total
50
50
5518
3.3.3.1 Option 1: Constant full-speed
Criterion
Cost
Feasibility of
Implementation
Longevity
Efficiency
Performance
Usability
Score
0.50
4
Estimated cost of basic analog components, (Mouser 2003).
We know how to implement this.
4
3
5
5
This would minimally tax the circuitry; we expect it to last.
This does not particularly save energy.
This would provide good cooling power.
This requires no input from the user.
3.3.3.2 Option 2: Run fan at low speed
Criterion
Cost
Feasibility of
Implementation
Longevity
Efficiency
Performance
Usability
Score
0.50
4
Estimated cost of basic analog components, (Mouser 2003).
We know how to implement this.
4
4
2
5
This would minimally tax the circuitry; we expect it to last.
This saves some energy.
This would provide poor cooling power.
This requires no input from the user.
3.3.3.3 Option 3: Run fan intermittently
Criterion
Cost
Score
1.00
Feasibility of
Implementation
Longevity
3
3
Efficiency
Performance
Usability
4
4
5
Estimated cost of basic analog components taking into
account added complexity for switching the fan on and off,
(Mouser 2003).
Requires some technical research.
The switching provides a greater tax on the circuitry,
making it more vulnerable to wear.
This saves some energy.
This would provide inconsistent cooling power.
This requires no input from the user.
3.3.3.4 Option 4: Manually controlled on/off
Criterion
Cost
Feasibility of
Implementation
Longevity
Score
0.50
4
3
Efficiency
Performance
3
2
Estimated cost of basic analog components, (Mouser 2003).
We know how to implement this.
The switching provides a greater tax on the circuitry,
making it more vulnerable to wear.
This saves some energy.
Cooling will be poorer since the fan will not be on all the
15
Usability
time and user may forget.
User has to turn fan on and off.
3
3.3.3.5 Option 5: Temperature-controlled fan
Criterion
Cost
Feasibility of
Implementation
Longevity
Score
1.50
3
3
Efficiency
Performance
4
3
Usability
5
Estimated cost, (Mouser 2003), (Phillips 2003).
Requires some technical research.
The switching and temperature sensors make it more
vulnerable to wear.
This saves some energy.
Cooling will be poorer since the fan will not be on all the
time.
This requires no input from the user.
3.3.3.6 Comparison Value Matrix
Fan Driver
Value Analysis
Market Constant Full Spd Low Speed
Quality
1 Efficiency
2 Performance
(Cooling Power)
3 Longevity
Value poin Value point
Total Value poin
Temperature
Total Value point
Total
3
180
4
240
4
240
3
180
4
240
100
75
5
4
500
300
980
2
4
200
300
740
4
3
400
225
865
2
3
200
225
605
3
3
300
225
765
Market Constant Full Spd
Value point Value point
Low Speed
Total Value point
Intermittent
Total Value point
Manual
Temperature
Total Value point
Total Value point
Total
25
5
125
5
125
5
125
3
75
5
125
80
4
320
445
4
320
445
3
240
365
4
320
395
3
240
365
Total
Market Constant Full Spd
Cost
1 Initial Cost
Manual
Total Value point
60
Total
Convenience
1 Usability
2 Feasibility of
Implementation
Intermittent
Total Value point
Value point Value point
100
0.5
Total
Customer Value: (Quality*Convenience/Cos
Low Speed
Total Value point
50
50
8722
0.5
Intermittent
Total Value point
50
50
6586
1
Manual
Total Value point
100
100
3157.3
0.5
Temperature
Total Value point
50
50
4779.5
Total
1.5
150
150
1861.5
3.3.3.7 Conclusion
From the value matrix above, the customer value for the constant full-speed fan is much
higher than the other four options. Since performance was determined to be of crucial
importance for the fan driver, and the constant full-speed fan provides high performance (cooling
power), we decided to use the constant full-speed fan.
16
3.3.4 Low Battery Indicator
We evaluated 5 potential methods by which to indicate a low battery status to the user.
This is intended to give the user some warning before the power supply shuts itself off. The
methods we examined include various output devices such as LED, LCD, audio and vibrating
signal. We also examined the possibility of flashing the main projector LED. The criteria used
to compare these options were cost, feasibility of implementation, performance, longevity and
usability.
3.3.4.1 Option 1: LED
Criterion
Cost
Feasibility of
Implementation
Longevity
Performance
Usability
Score
0.07
4
LVG2043 (Jameco 2003)
We know how to implement this.
4
5
5
This would minimally tax the circuitry; we expect it to last.
This meets performance needs.
Easy to use, non-disruptive
3.3.4.2 Option 2: LCD
Criterion
Cost
Feasibility of
Implementation
Longevity
Performance
Usability
Score
2.98
2
LCD-S101D14TR (Mouser 2003)
We do not know how to implement this yet.
3
5
5
This device is relatively fragile
This meets performance needs.
Easy to use, non-disruptive
3.3.4.3 Option 3: Audio signal
Criterion
Cost
Feasibility of
Implementation
Longevity
Performance
Usability
Score
1.05
3
253-4020 (Mouser 2003)
We have some idea of how to implement this yet.
4
5
4
This would minimally tax the circuitry; we expect it to last.
This meets performance needs.
Could be disruptive.
3.3.4.4 Option 4: Flash main (projector) LED
Criterion
Cost
Feasibility of
Score
0.50
3
Estimated cost of basic analog components, (Mouser 2003).
We have a good idea of how to implement this.
17
Implementation
Longevity
Performance
Usability
4
4
3
This would minimally tax the circuitry; we expect it to last.
This has the potential to disrupt use of the product.
The potential for the LED to flash more than once as the
voltage goes through slight fluctuations could be a
disruptive
3.3.4.5 Option 5: Vibration alarm
Criterion
Cost
Feasibility of
Implementation
Longevity
Performance
Usability
Score
2.99
2
KHN4NB1N (Digi-Key 2003)
We do not know how to implement this yet.
3
4
3
Moving parts make it prone to wear and tear.
Vibration might cause damage to the projector.
Vibration might disrupt the class.
3.3.4.6 Comparison Value Matrix
Low Battery Indicator
Value Analysis
Market LED
Value point
Quality
1 Performanc
40
2 Longevity
75
LCD
Value point
5
4
Total
200
300
500
Market LED
Convenience
1 Usability
2 Feasibility
of
Implement
ation
Total
5
3
200
225
425
LCD
Value point Value point
Total
Value point
5
4
Flash Main LED
Total Value point
200
300
500
Audio Signal
Value point
Total
Value point
Vibration Alarm
Total Value point
4
4
160
300
460
Flash Main LED
Total
4
3
160
225
385
Vibration Alarm
Total
Value point
Total
Value point
Total
25
5
125
5
125
4
100
3
75
3
75
80
4
320
445
2
160
285
3
240
340
3
240
315
2
160
235
Total
Market LED
Cost
1 Initial Cost
Audio Signal
Total Value point
LCD
Value point Value point
100
0.07
Total
7
Total
7
Customer Value: (Quality*Convenienc 31,785.70
Audio Signal
Value point
2.98
Total
298
298
406.50
Value point
2.99
Flash Main LED
Total
299
299
568.60
Value point
0.5
Vibration Alarm
Total
50
50
2,898.00
Value point
1.05
3.3.4.7 Conclusion
The results of the value matrix show that an LED low-battery indicator is a superior
choice. The second best choice would be to flash the main (projector) LED, but this is slightly
less straightforward to implement and may lead to some usability issues. Since the LED
18
Total
105
105
861.70
indicator has such a higher score than the others, we are inclined to believe this to be the option
that best meets the customer needs.
3.3.5 Circuit Protection
We evaluated 3 potential methods by which to protect the circuitry from excessive
voltages and currents. The methods we examined were circuit breaker, fuse and protection relay.
The criteria used to compare these options were cost, cost of replacement parts, feasibility of
implementation, performance, longevity and usability.
For the battery protection circuit we decided to weight the performance more heavily, at
100. We determined that performance for this particular component is crucial since the
consequence of poor performance would be a damaged automobile battery.
3.3.5.1 Option 1: Fuse
Criterion
Cost
Cost of
Replacement Parts
Longevity
Performance
Usability
Feasibility
of
Implementation
Score
0.62
0.12
Estimated component cost, (All Electronics 2003).
Replacement cost of fuse.
1
4
3
3
Fuse needs to be replaced once used.
Protects the battery fairly well.
User has to replace fuses
We have some idea of how to implement this.
3.3.5.2 Option 2: Circuit Breaker
Criterion
Cost
Cost of
Replacement Parts
Longevity
Performance
Usability
Feasibility
of
Implementation
Score
0.50
0
Estimated component cost, (All Electronics 2003).
Should not need to be replaced.
4
5
5
3
Built for longevity.
Provides robust protection.
We found one with an auto reset as the circuit cools.
We have some idea of how to implement this.
19
3.3.5.3 Option 3: Relay
Criterion
Cost
Cost of
Replacement Parts
Longevity
Performance
Usability
Feasibility
of
Implementation
Score
0.50
0
Estimated component cost, (All Electronics 2003).
Should not need to be replaced.
4
5
5
2
Built for longevity.
Provides robust protection.
Nothing for user to do.
We are not very familiar with this concept.
3.3.5.4 Comparison Value Matrix
Circuit Protection
Value Analysis
Market Fuse
Quality
1 Performance
2 Longevity
Circuit Breaker
Total
Value point
4
1
400
75
475
5
4
Value point
Value point
Total
Value point
25
3
75
80
3
240
315
Value point
Value point
Total
Value point
100
0.62
62
100
0.12
12
74
Value point
Value point
100
75
Total
Market Fuse
Convenience
1 Usability
2 Feasibility of
Implementation
500
300
800
Market Fuse
500
300
800
Total
Value point
Total
5
125
5
125
3
240
365
2
160
285
Total
Value point
Total
0.5
50
0.5
50
0
0
50
0
0
50
Relay
Circuit Breaker
Total
Customer Value: (Quality*Convenience/Cost)
2022
Total
5
4
Circuit Breaker
Total
Cost
1 Initial Cost
2 Parts
Replacement
Relay
Total Value point
Relay
5840
4560
3.3.5.5 Conclusion
From the value matrix above, the results show that the circuit breaker and relay seem to
be the best options for our design. We chose a circuit breaker due to the greater ease of
implementation. However, during design we determined that to get a circuit breaker that
adequately met our specifications, the cost would be significantly increased to about $1.27 at
quantities of 1000. It is possible that the relay option should be explored for later versions of this
device.
20
3.4 Design Option Conclusions
The brainstorming sessions proved quite fruitful in producing possible design approaches
for each of the subsystems within our power supply. The design options analysis makes clear
that there are many trade-offs to assess. We have given such a high priority to creating a lowcost device that we sometimes might be sacrificing performance and durability to reduce cost.
The inexact quantification of the value criteria assist us in analyzing these decisions, however
these decisions should be revisited in the next design cycle. We recommend that the next
engineers to modify this power supply revisit those decisions based on the information about
product performance of our prototype.
21
4 Architectural Description of Power Supply
The product consists of circuit protection, low battery protection and indication, a manual
on/off switch, an internally-controlled switch and the LED driver. Since we have determined
that the fan can simply run in parallel with the LED driver and does not require any drive
circuitry, we have not included a fan driver functional block.
4.1.1 Block Diagram
Figure 3: Functional Block Diagram
22
4.1.2 Module Overview
The LED driver provides power to the light-emitting diode (LED) of the projector. The
LED itself is the crux of the projector technology, so this module is essential to the device’s most
basic operation. This module needs to conserve power, while maintaining a constant and strong
brightness in the LED. The LED driver uses pulse-width modulated current regulation to drive a
Buck DC-DC converter. Although our first inclination was to use solely discrete components;
further analysis has shown an integrated circuit in conjunction with discrete components would
be the most effective and cost efficient option.
The fan driver’s task is to provide power to the fan. Although it has been eliminated
from the functional block diagram it has remained in this report in order to provide the most
complete analysis of our circuit design. This module must accommodate a wide range of input
voltages and must allow the fan to reliably cool the projector’s LED. This part of the design is
necessary because of the characteristics of the projection method. The LED places a large
thermal load on itself and the rest of the components within the projector. In order to run the
device reliably it is necessary to cool the projector’s internals with a fan. Without the necessary
precautions to ensure correct operation of the fan, it is possible to have complete failure of the
projector. Fortunately, the characteristics of DC fans will allow ours to operate directly from the
full range of battery inputs that we can expect. The design for the fan driver has not had any
significant changes. Based upon the experimentation and analysis we have performed we believe
our design best meets our customer and product requirements.
The purpose of the low battery protection and indicator module is to automatically shut
down the device before over-depleting the battery and to provide the user with some advanced
warning of this shutdown. When the battery voltage drops below a set minimum value, the
module illuminates a small LED. This indicates to the projector’s operator that the battery
voltage is getting low. This module is a necessary portion of our overall design because it is
important that our power supply prevent damage to the battery. One source of potential damage
to the battery is its depletion below the manufactures specified minimum voltage level. This
module prevents the possibility of this form of damage by shutting down the connection to the
fan and LED driver. The design of the low battery indicator has not undergone any significant
revisions since the previous design.
The circuit protection module of our design must protect our circuitry from harmful input
scenarios. One such scenario is the reversal of the inputs from the battery. Another potentially
harmful condition could arise if excessive voltage is placed across the input terminals to the
power supply. It is possible this condition could happen in the event of a battery charger
malfunction while the charger and projector are connected to the battery at the same time. Yet
another possibility is that a short circuit condition within kinkajou projector or the power supply
itself could arise. In these events we must prevent damage to the battery, if possible, as well as
protecting the power supply, LED and fan. From the customer requirements it is obvious that
this level of protection is necessary. The power supply must account for possible failures and
prevent these occurrences from causing damage. Testing of this design has proven the
effectiveness of this module.
23
4.2 Product Description by Module
For each module, we have analyzed its input and output values as they relate to the
functions performed. Though we intend to design the circuit to cease operation when the input
voltage is less than 11V or greater than 16V, we will calculate our values based on a range of
10.5V to 16.5V to allow for small errors in operation. Also, we will calculate our typical values
based on a battery voltage of 12.
4.3 LED Driver
4.3.1 Design Approach
For the LED driver, we have chosen to implement a Buck converter with a pulse-width
modulated switch. This is a traditional DC-DC step-down converter designed to minimize power
consumption. The pulse-width modulation is handled by an integrated circuit, (National chip
LM3578A), which controls a transistor that switches on and off to only draw power from the
battery for a fraction of each cycle. This pulsing signal is then converted to a constant DC output
by an inductor, diode and capacitor. We also considered designing the pulse-width modulator
ourselves using discrete components, but determined that an integrated circuit could provide a
more robust design in a small and reasonably-priced package.
4.3.2 Functions
The LED driver functional block represents the crucial part of the system responsible for
powering the projector LED, a Luxeon V Portable White. The LED driver needs to be efficient
and provide a constant current to the projector LED. Due to the steep current-voltage
relationship of this LED, regulating the current will provide a more consistent light output than
attempting to regulate the voltage, (Lumileds 2002).
4.3.3 Outputs
All of the LED driver output will go to the projector LED, and so the requirements of the
LED determine the input and operation of the driver. The projector LED requires 700mA at a
typical voltage of 6.84V, and a range from 5.43 to 8.31V, (Lumileds 2002). Although a
switching converter is used, the output provided to the LED should be a constant DC current of
700mA, the AC component will be filtered by the capacitor (C2E).
4.3.4 Inputs
The battery voltage less any drop across the internal switch and circuit protection
modules will be the input to this functional block. Since the switch and protection voltage drops
are expected to be negligible, we will assume a broad range of voltage input (10.5-16.5V). For
average calculations, we will use VIN = 12V.
24
We have calculated the expected current and power drawn by this module. The power
out of the module is the power over the LED. Power dissipated includes the power over the
current regulating resistor, R1E, which has a voltage drop of about 1V (V=IR, I=700mA). There
will also be power dissipated in elements such as the diode. The diode we selected based on
price does not have power dissipation in their datasheet, but the diode is similar to the Fairchild
1N5818 Shottky, the power loss would be approximately 1.25W for the fraction of each cycle
that the diode is in forward active mode, (Fairchild 2001). There is also dissipation in the
transistor which is at most 1W, (Zetex 1994). The voltage out/in relationship dictates the duty
cycle of the switch and therefore the fraction of time for which the diode and transistor is active.
Using VIN=12V, VR1E=1V, VLED=6.84V, ILED=700mA, PDIODE=1.25W
PIN = PLED + PLOSS
PLED = VLED * ILED = 6.84V * 700mA = 4.8W
PLOSS = D * (PDIODE + PTRANSISTOR) + PR1E
PR1E = VLED * ILED
D = VOUT/VIN
PLOSS = ((6.84V+1V)/12V)*(1.25W + 1W) + 1V * 700mA
PLOSS = 2.17W
Average (DC) Values:
PIN-DC = 6.97W
IIN-DC = PIN / VIN = 6.97W /12V = 0.581 A
PIN-DC < 7.18W
413mA < IIN-DC < 680mA
Absolute Maximums (Peak Values):
PIN <= 7.25W
IIN <= 1A
The current drawn by the IC will not significantly impact these calculations. The LM3578A,
draws 2mA when switch is open and 14mA when switch is closed, (National 1998). Please note
that these calculations are theoretical, not experimental. In most cases, these should be very
conservative estimates.
4.3.5 Operation
4.3.5.1 Buck DC-DC converter
The Buck converter uses a switching regulator and a low-pass filter to provide direct
current to the projector LED. Since the LED requires less voltage than will be provided by the
battery, the voltage needs to be reduced. The Buck converter is more efficient than a voltage
regulator or voltage divider. These options draw the full current needed at the output and
dissipate the unused power as heat, thus wasting battery life and unnecessarily heating the
circuit. The duty cycle of the Buck converter is determined by the voltage out/in ratio, (D =
VOUT/VIN).
25
When the switch is closed, the voltage source will be connected to the rest of the circuit,
powering the LED and charging the capacitor. When the switch is open, the capacitor will
discharge and current will flow through the diode. The LED will continue to have the same
current through it. The inductor and capacitor act as a low-pass filter, absorbing the AC
component of the current. The LED only sees a DC average current.
4.3.5.2 Pulse-Width Modulation
The pulse-width modulation for this circuit should be based on current, since we are
trying to regulate the current for optimal performance. The pulse-width modulation circuit will
control the duty cycle of the Buck converter in order to achieve the desired output. In order to
regulate current, we put a resistor, R1E, in series with the projector LED and infer the current by
comparing the voltage drop across the series resistor to the resistance, (I=V/R). This voltage is
compared to a 1V internal reference in the switching regulator chip, LM3578A. Therefore the
resistor is selected based on I=V/R, V=1V, I=700mA. A resistor of 1.43 ohms would be ideal,
but we selected 1.5 ohms, which was a more easily available value. The resistor also has a 5%
margin of error. The non-ideal value and margin of error will affect the output current to the
projector, however since we are regulating current, we should have more leeway to provide a
non-exact value and still achieve good performance from the projector LED.
4.3.6 Schematics
The design of the LED driver centers around the LM3578A, a switching regulator
integrated circuit (IC), which we are using to regulate a Buck DC-DC converter. The switching
regulator includes a switch which runs in opposition to the external switch, Q1E. The regulator
switch input is at pin 6 and the output at pin 5. Pin 7 is used for current limiting, which we are
not using since we are regulating current already, and pin 8 provides the input voltage for the
component. Though designed for voltage regulation, this IC can be made to use current
regulation by testing the voltage over a resistor, R1E, that is in series with the output LED, D2E.
The regulator controls the switch Q1E which is used to boost the current. This current boost is
controlled by R2E and R3E. The potential difference over the resistor is compared to an
internally regulated reference voltage. The low-pass filter, L1E and C2E, and Shottky diode,
D1E, completes the Buck converter causing the output to receive direct current. This design is
based on a current boosted buck converter from the LM3578A datasheet, (National 1998).
26
Figure 2: Schematic for LED driver
4.3.6.1 Component Value Selection
VREF is the internal reference voltage to which the voltage from pin 1 to pin 2 is compared.
For the LM3578A, this is 1V, (National, 1998). IOUT is the current over the projector LED, (D2E).
Our goal is that IOUT=0.7A.
R1E = VREF/IOUT = 1V/0.7A = 1.43 Ohms
We are using a resistor with a nominal 1.5 Ohms, which is a more standard value. Due to
the steep I-V curve of the Kinkajou LED, we have more flexibility with the current regulation than
we would have with voltage regulation. Therefore, we do not believe that the difference introduced
by using a non-exact resistance and the error in the resistor will significantly affect our desired
output.
Transistor base resistors R2E and R3E control the current to the base and are necessary for
correct operation of the device. We tested the β value of the transistor and found it to be about 130.
VBE = 0.8V
VSAT = 0.7V
VIN = 12V
IL(MAX-DC) = 0.7A
Ip = 0.79A
R2E = 10*VBE*β / Ip = 1.3kOhms
IR2E = 0.8 V/ 1.3kOhms
R3E = (VIN – VR1E - VBE - VSAT)*β / (IL(MAX-DC) + IR2E) = 1.9kOhms
Values for VBE and VSAT and equations came from the transistor datasheet, (Zetex 2003).
We used average values to calculate the proper resistor values. We selected a 2kOhm resistor for
R3E, which is a more readily available value. The resistors we selected have 5% tolerance.
27
We used the Buck converter inductance equation to determine the inductor minimum based
on the acceptable current ripple, (National 1998).
L = Vo(V1-Vo)/∆ILV1fosc
Vo = VLED + VREF
fosc is 50kHz. We decided to use ∆IL = 0.300A, since we are attempting to achieve and
output current of 0.7A, and the absolute maximum for the Kinkajou LED is 1A, (Lumileds 2002).
By calculating the minimum inductances for a range of input and output voltages, we can determine
a safe minimum inductance.
10.5V <= V1 <= 16.5V
5.43V <= VLED <= 8.31V
L for these domains is 274.3uH
274.3uH is the minimum inductance required for no more than a 0.300A current ripple
through the inductor at our full range of inputs and outputs. In general, we would prefer a smaller
ripple. For our average input of 12V and Vo of 7.84V, (1V across R1E + 6.84V over D2E), we
have calculated the minimum inductance for a 0.180A ripple to be 302uH. We have chosen an
inductor that is 330uH because it was the most reasonably priced one we found that could handle
the current.
Testing revealed that the best value for C2E was 100uF. Further development of this
module could include more precise calculations for this value. However, since this is a common
value for a capacitor, they are readily available and inexpensive. I5 is the current coming from the
regulator switch into the Buck converter. This has a ripple which is filtered out by the capacitor
(C2E).
I5 < 0.880A
From the LM3578A datasheet recommendations, (National 1998):
C3E = 20pF
C1E = 1820pF (We chose 1800 which was more readily
available.)
Through testing, we found the need for a capacitor from the input to the ground, C4E. This
compensates for the non-ideality of the voltage source and inductance due to the length of the leads
between the device and the voltage source (battery). Our empirical results showed that a 10uF
electrolytic capacitor solved the problem. This capacitor is extremely important; based on our
testing, the LED driver will not work without it.
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4.3.7 Testing
We tested the LED driver using a range of input voltages and modeling the Luxeon LED
with a 10Ohm resistor. The current remained consistent over a range from 10.5 to 16V, supplying
the load with about 650mA of current.
4.3.8 Problems and Recommendations
The LED driver provides constant current to the load (projector LED), however this current
is not exactly 700mA due to the imprecision of the current sense resistor, R1E. This resistor can be
replaced with one closer to the ideal 1.43 Ohm value and/or a resistor with a smaller percent error.
Another possibility would be to fit the prototype with some sort of variable resistor controlled by a
potentiometer. In this way, one could test the effect of various resistances on the output.
This LED driver was never tested with the Luxeon 5W LED. Rather, a 10Ohm load was
used in place of the LED. Obviously, this needs to be tested with the actual LED. In addition, this
device was not tested for extended periods of time, which we recommend.
We have noticed that the transistor gets quite hot during operation, and so a heat analysis
should be done and we anticipate that a small heat sink would be needed.
4.4 Fan Driver
4.4.1 Functions
The function of this circuit is to control the operation of the projector’s cooling fan. This
module must provide that the fan operate under the manufacturer’s specified conditions so as not to
damage the fan. The cooling fan operation is integral to proper operation of the projector. As
stated previously we have decided to eliminate the module from the functional block diagram
because our testing has proven that no special care is necessary to ensure the correct operation of
the fan. The fan driver module is included in this section to allow us to describe how these
conclusions were reached and provide some experimental results which back up the claims we
make about the fan’s operation.
4.4.2 Inputs
The input to the fan driver is a voltage of no less than 11 volts and no greater than 16 volts.
The modules preceding this in the power supply limit the input voltages to between these two
levels.
4.4.3 Outputs
The output of this module must be a range which falls within the manufacturer’s datasheet
for the fan. Fortunately the inputs which we are given to this module lie within the ranges of most
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12 volt DC fans. The team was somewhat cautious about the fan’s ability to accept this wide range
of inputs, so we decided to do some testing of our own. See section 3.2.6 for our analysis.
4.4.4 Operation
The power dissipated by the fan can be calculated using simple fundamental equations.
Design that Matters has provide us with this description of the fan that can be found on the course
website: “40mm 12VDC 110mA fan blows 9 CFM at 1 watt.” (Vaz 2003)
I = 110 mA
P = 1Watt
P = VI
Given these characteristics it must be assumed that the potential at which the power
dissipated equals one watt and the current drawn equals 110mA is at a rating of 9 Volts. At a
nominal 12 Volts the fan would draw 1.32 Watts and at 16 Volts the fan would draw 1.76 Watts.
4.4.5 Schematics
We will be running the fan driver in parallel with the LED driver in a configuration similar
to that in Figure 3.
Figure 3: Schematic for fan driver
4.4.6 Testing
Optimally the team would have liked to test the exact fan used in the Kinkajou projector. At
the time of the experiment however, the particular fan was unavailable. After consulting many
manufacturers’ datasheets for a variety of fan types, we were able to make some helpful
generalizations. Brushless DC fans, like the type used to cool computers and other electronic
equipment, can be designed to operate on different voltage levels. The one we are working with
happens to be a 12 volt model. The team also learned that these devices are not particular about the
exact operating potential; rather a fan will accept a wide range of voltages. The 12 volt models
typically accept a range of inputs from 8-16 volts DC. As stated previous, we know our inputs to
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the fan driver fall within this range. In order to ease any doubt about this finding we brought the fan
to the lab for some testing.
From our research we were able to make some generalizations about DC fans with similar
voltage and current ranges. This allowed us to substitute a readily available fan for testing. In this
case we chose a Sunon 12 volt 80mm DC cooling fan model number KDE 1208PTB2-6. The fan
was connected to a power source much as it will be in our project. The input source was selected so
that it could supply in excess of the .166 mA that the fan is rated to draw (Sunon 2002). Next
voltage of the source was chosen to supply 12 volts DC. This is the nominal input voltage we
expect to the fan. The fan was connected to the source and ground, power was then applied. As
expected the fan turned on and ran at a steady speed. Lacking a tachometer we were unable to
measure the fan’s speed, although we would have liked to ensure the fan did not exceed its
maximum rpm rating provided by the manufacturer. Next the voltage was decreased to the 11 volt
minimum input. The speed of the fan decreased. The voltage supply was then increased to the 16
volt maximum input rating. The speed of the fan increased and remained constant. Based upon the
crude experiment we are fairly convinces that we have made the right decision about the design of
the fan driver circuit.
4.4.7 Problems and Recommendations
Testing of the cooling efficacy of the fan when using our power supply would be the next
step in verification of the module.
4.5 Internal On/Off
4.5.1 Functions
The internal on/off switch allows the battery protection block to control whether the battery
is connected to the LED and fan drivers.
4.5.2 Inputs
The current required for the fan and LED drivers will pass through this switch. We have
determined this current to be less than 2A, and never more than 3A (since the circuit protection
block will not allow anything higher). The voltage at the battery side of the switch will be
effectively the same as that of the battery (10.5-16.5V), less any drop across the circuit protection
block. The input to the base of the transistor can be determined by changing resistor values in the
battery protection module. In this manner we can control the input so that it is of an acceptable
range for the transistor. The input to the base of the transistor will come from our battery protection
circuit. For our switch the requirement is a voltage between 1.25 and 5 V at a current of 200mA
(Zetex 1994).
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4.5.3 Outputs
The switch we have chosen is a PNP medium planar transistor made by Zetex.
Unfortunately we were forced to make some compromises with the switch we choose for our
design. Although we would have liked to have done better, the transistor dissipates 1 W of power at
2 amps, (Zetex 1994). In our implementation we expect about 1.3 amps of current through the
transistor so our power loss should be less. The saturation voltage across the collector and the
emitter of the transistor ranges from 0.23 to 0.5 V at 2 A of current (Zetex 1994). This will cause
the output of the switch to be about this much lower potential than the input to the switch.
4.5.4 Operation
When the battery protection block determines that the battery voltage too low, the switch is
turned off by an applied signal to the base of the transistor. This will block current to the fan and
LED driver. Otherwise, the switch is on.
4.5.5 Schematics
The implementation of this switch can be seen in the schematic for the battery protection
module (Figure 4).
4.5.6 Testing
The internal switch was tested by applying the range of inputs expected in a test
environment. The switch operates as anticipated.
4.6 Low Battery Protection and Indication
4.6.1 Functions
The function of this module is to indicate when a battery voltage drops below a certain value
and to shut off the device before the battery is so depleted that it could cause damage.
4.6.2 Inputs
In normal operation, input range is from 11V to 16V, though we will calculate values based
on extended range of 10.5-16.5V. This circuit also needs to be able to respond correctly to voltages
lower than 11 by shutting off the rest of the device. We assume 12V is average input voltage from
the battery. The resistive dividers will draw a total of 1mA.
The power consumed by this module is minimal. The power consumed by the resistive
dividers (P=IV) will range from 0.01 to 0.02 W. The power consumed by the comparators
themselves will be less than 830mW, (National 2002).
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4.6.3 Outputs
According to a datasheet from National Semiconductor, typical output current from a
comparator such as the LM358 is 40mA with output voltages from 8 to 14V, (National 2002).
From the V-I characteristic of the low battery indication LED, 40mA is enough to run the LED,
(Marktech 2002). According to the datasheet from National Semiconductor, output voltages of our
op-amps (LM358) are:
Vout = VSUPPLY − 1.5V (National 2002)
Using the input range, 10.5V-16.5V, the range of the output voltage is from 9V to 15V.
4.6.4 Operation
4.6.4.1 Low Battery Indication Comparator
For the low battery indication comparator, when the potential difference from V+ to V- is
positive, the voltage is below the warning threshold and output current flows turning on the warning
LED. When the drop is negative, the voltage is above the warning threshold and no current flows.
The voltage regulator LM78L05 converts input voltage to 5V, (National 2003). For the comparator
(U1A) in Figure 4, V+ is 5V, and V- changes as VIN changes. We used a voltage divider to create
the appropriate comparison values from VIN. An equation for V- is:
V- = VIN*[R3/(R2+R3)]
When VIN is 11.5V, V- is 5V. We have computed R3 to be 10kohm and R2 to be 13kohm.
Low battery indication LED behavior is shown in Table 1.
VIN (V)
VIN >= 11.5
VIN < 11.5
LED
Off
On
Table 2: Relationship between VIN and protection LED
4.6.4.2 Switch Control Comparator
For the comparator (U2A) in Figure 4, V+ is always 5V from the voltage regulator and Vchanges as VIN changes. We will again use a voltage divider to create an appropriate voltage for
comparison. An equation for V- is:
V- = VIN*[R4/(R4+R5)]
When VIN is 11V, V- is 5V. We have computed R2 to be 12kohm and R5 to be 10kohm.
The internal on/off switch behavior is shown in Table 2.
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VIN (V)
VIN >= 11
VIN < 11
Switch
On
Off
Table 3: Relationship between VIN and internal switch
In order to prevent the projector LED from switching on and off as VIN hovers around the
threshold value, the comparator employs Schmitt trigger. The hysteresis characteristic will prevent
this problem from occurring. The Schmitt trigger threshold voltages V+hi and V+low are:
V+hi = V+ + 5*(R9/R8)
V+low = V+ - 5*(R9/R8)
When V- drops to below V+low, the switch is turned off and the switch stays off until Vgoes up to V+hi. This Schmitt trigger behavior would not be reset until the external switch is turned
off. We have computed R4 to be 12kohm, R5 to be 10Kohm and R8 to be 510kohm. At 10.78V,
the control switch is off, and the switch is turned on again when Vin goes up to 11.21V. For Schmitt
trigger, once V- reaches V+low, the switch is turned off. After that, the switch is never turned on
until V- reaches V+hi which is when VIN is 11.21V.
4.6.5 Schematics
Figure 4 shows the schematic for this module. Comparator U1A is used to determine
whether the battery voltage is lower than ~11.5V, lighting the low-battery indicator LED if it is.
Comparator U1B determines whether the battery voltage is higher than 11V, turning on the internal
control switch (Q1) if it does. The regulator provides a constant reference to the comparators.
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Figure 4: Schematic for battery protection
4.6.5.1 Component Value Selection
Component value selection for R2, R3, R4, and R5 is discussed in section 3.34. From the
typical application on the LM78L05 datasheet C2 is 0.33uF and C1 is 0.01uF, (National 2003).
When VIN is less than 11.5V the indication LED is turned on, and a voltage drop across LED is
typically 2.1V. From the datasheet of the LED, the maximum forward current is 30mA (Marktech
2002) and a few mA of current is needed to turn on the LED. Current I1 which go through R1 is:
I1 = (Vout – 2V)/R1
Based on this equation, we have computed R1 to be larger than 317ohm. However, in order
to reduce power dissipation, we have chosen to use a much larger value of resister 3kohm resistor,
because it is a standard resistor value.
4.6.6 Problems and Recommendations
Precision of monitoring voltage is big problem of this module. The biggest impact on
precision is the error in the voltage regulator, but the error in the resistors also plays a part. With
our current 5% tolerance on the voltage regulator and resistors, the automatic shut-down voltage
could range from 9.91 to 12.21V, and the warning light could turn on anywhere from 10.34 to
12.79V.
35
The voltage regulator (LM78L05) has 5% output voltage tolerance. We found out there are
many voltage references with a smaller output tolerance. Table 3 shows the voltage regulator
(LM78L05) and one of the cheapest voltage references from Digikey. Since the voltage reference
has much less tolerance and is only $0.02 more expensive than the voltage regulator, the voltage
reference should be used for this module, (Digikey 2003).
Component (Manufacturer)
Voltage Regulator
(Fairchild LM78L05ACZ)
Voltage Reference
(Texas Instruments
LM385LP-1-2)
Output Voltage
Tolerance
±5%
Cost per piece
(1)
$0.45
Cost per Piece (800)
±2%
$0.50
$0.17
$0.15
Table 4: Cost Analysis of Voltage Regulator and Reference
In the prototype of our product, 5% tolerance resistors are used. 5% resistors make a large
range of value of voltage when the LED is turned on and when the switch is turned off. We
analyzed the range of LED “On” and Switch “Off” voltages for 5% resistors if a 2% voltage
reference is used. Table 4 shows that using 5% tolerance resistors may damage the battery by
running it lower than the 10.5V minimum or turn off the power supply far too early. As shown in
table 5, using 1% tolerance resistors provides a more precise range and the power supply will not
damage the battery.
Vin (LED “On”)
Vin (Switch “Off”)
Min (V)
10.34
10.22
Ideal (V)
11.5
11.0
Max (V)
12.79
11.86
Table 5: Low Battery Protection/Indication Performance with 5% resistors (V= 5V +/-2%)
Vin (LED “On”)
Vin (Switch “Off”)
Min (V)
11.80
10.66
Ideal (V)
11.5
11.0
Max (V)
12.21
11.34
Table 6: Low Battery Protection/Indication Performance with 1% resistors (V= 5V +/-2%)
A potentiometer makes more precise voltage monitoring module. The potentiometer can be
used between voltage divider and replacement of one resistor from voltage divider. The
manufacturer can adjust Vin so that the module will be the most precise. See table 5 for a
comparison of price for 5% resistor, 1% resistor, and a potentiometer, (Digikey 2003). The major
drawbacks to using a potentiometer that is tuned for each product is high cost of component and a
more labor-intensive manufacturing process.
Component (Manufacture)
5% resistor (Yageo)
1% resistor (Yageo)
Cost per piece (1)
$0.056
$0.10
36
Cost per piece (800)
$0.019
$0.041
Potentiometer
(Bourns Inc. 3309P-1-202)
$0.56
$0.289
Table 7: Cost of 1% and 5% Resistors
In conclusion, we recommend that 1% resistors and a 2% voltage reference for this module.
At the very least, the 2% reference should be used because the current possibilities of inaccuracy are
not acceptable.
4.7 Circuit Protection
4.7.1 Functions
The function of the circuit protection module is to protect the power supply from excessive
voltage, excessive current or reverse polarity situations. We believe these sscenarios present a
realistic threat to our power supply circuitry. As our client, Design that Matters, described to us, the
power supply must be able to operate off the battery power, whether or not the charging circuit is
connected. One possible danger to our power supply could arise when a malfunctioning charger is
hooked up to a battery from which our power supply is drawing power. From speaking with battery
charger engineering teams, we have learned that a properly operating charger will output no more
than 16 volts. As we have learned from these teams, any voltage higher than this poses great danger
to the battery itself. For this reason we have decided to limit the input voltage to our power supply
at 16 volts. We believe this will allow our device to run in conjunction with the charger, while
limiting the risk to our circuitry and the projector itself.
Another important part of our protection module is reverse polarity protection. Our device
is designed to safely operate only under correct polarity. However, we realize that a reversal of
polarity is a real possibility. Given the un-keyed, often poorly labeled terminals of some batteries it
is highly likely that at one time the leads to the battery terminals could be reversed. Given this
scenario it is necessary to protect our power supply and the projector from any damage.
4.7.2 Inputs
The inputs to the module could range from in excess of 16 volts, given connection to a
malfunctioning charger, to lower than 11 volts if connected to a severely depleted battery. In
normal operation, total current through the module depends upon the modules connected after this
one. A reasonable estimate of the current that exceeds the maximum the circuit will need to handle
is 2 Amps.
4.7.3 Outputs
The module will limit the output voltage to less than 16 volts. For any potential greater than
this, the circuit breaker will trip requiring it to be reset. It will be up to the operator to debug the
source of this problem. Unless the situation is remedied the circuit breaker will continue to trip
upon being reset. Low voltages will not be limited by this module, but are handled by the battery
protection module. The output current will be limited to 3 Amps. We chose a circuit breaker with a
37
rating of 3 Amps because we expect our power supply to draw less than 2 Amps. Given that we do
not want our circuit breaker to trip unless necessary, we provided additional leeway in the amount
of current the circuit breaker will allow through. 3 Amps should provide us with the protection we
desire and the performance we require.
The output of the module is guaranteed to be in the orientation we expect. That is, the
battery is guaranteed to be connected with the polarity we anticipate. By ensuring this, we can
make our decisions in the rest of the power supply with the confidence that the battery leads will
have the correct polarity.
4.7.4 Operation
For situations in which the orientation of the battery leads has been reversed the equivalent
flow of positive charge would be from the ground node, up through diode D1M and out through the
circuit breaker SB1M to negative terminal of the battery. This creates a short circuit condition
within the power supply. The excessive current through the circuit breaker would cause it to trip
creating an open circuit condition and stop all current flowing through the power supply. In
situations where the polarity follows the convention we have given on our schematic, no current
flows through the diode D1M.
In reverse polarity situations, the power consumed in this subsection of the circuit is given
by the square of the current through the diode (D1M), times the sum of the resistances of the circuit
breaker (CB1M) and the diode (D1M) itself. In order for the reverse polarity protection to work, we
are assuming that these resistances will be so low the circuit will act as a short circuit. Given a
short circuit at this point, all the current will flow through the diode D1M. No current will flow
through any other portion of the circuit and no power will be dissipated in any other portion of the
circuit as well. If the resistances of the diode and circuit breaker are so small as to be ignored, than
the power lost is also negligible.
In correct polarity situations, the power consumption can be determined by taking the
voltage across the diode (D1M) and multiplying it by the leakage current of the diode. In this case
we are making the assumption that the resistance of the diode is infinite as to act like an open
circuit. This makes the leakage current of the diode very small. If the leakage current is small
enough for us to ignore, then a negligible amount power is lost through the diode in normal
operating conditions.
Given correct polarity, and input voltage less than 16 volts, the power dissipated by the
voltage protection sub-circuit is also negligible. Following the same rational as above, the leakage
current through the Zener diode (D2M) can be ignored and acts like an open circuit. Consequently,
no current flows in to the gate of the silicon controlled rectifier (SCR1M) and current is prevented
from flowing though main path of the SCR. Of course this component is not ideal and some small
amount of current will flow through the device. However this current is so small that the power
consumption can again be ignored.
In situations where voltage is greater than 16 volts the following chain of events occurs.
The Zener diode (D2M) is chosen to have a threshold voltage of 16 volts. Once that potential
38
difference is seen across the diode, current is allowed to flow against the normal orientation. Some
of this current charges the capacitor (C1M), some of the current flows over the resistor (R1M) to
ground, and the remaining portion reaches the gate of the silicon controlled rectifier (SCR1M).
Once a small amount of current reaches the gate of the SCR the cathode junction is in a state of
forward bias and SCR will turn on completely (Bigelow 2003). This creates a short circuit
condition where the circuit breaker is tripped and current into the power supply is cut off by the
resultant open circuit. In case the diode’s threshold voltage is only reached momentarily, the charge
on the capacitor will ensure that the SCR remains forward biased long enough to trip the circuit
breaker. Of course this will dissipate power when this happens. Power will be used to charge the
capacitor; some will also be lost across the resistor to ground. Additionally losses will be seen in
the diode and the SCR as well. However, because this condition results only for the time it takes
the circuit breaker to react, we can ignore these losses if we assume the circuit breaker reacts
quickly to the excessive current.
4.7.5 Testing
Testing for this module is complete. The test began with experimenting with the function of
the SCR. Since this was a first time working with the part, the team thought it would be wise to
experiment with its operation before testing it as part of the larger circuit protection buffer. After
the SCR’s proper operation was thoroughly understood the rest of the circuit was laid out on the
breadboard. An input source was connected to the input voltage reference of the schematic. At the
output we connected a multimeter to measure the output voltage of the circuit protection buffer.
Given correct orientation of the battery leads as well as a potential below 16 volts. The
output of the protection module should be the same as the input. This operation was confirmed in
the laboratory. For input voltages from 0 volts to 16 volts the output corresponded directly to the
input.
Given correct polarity and a potential greater than 16 volts, the result should be a tripped
circuit breaker and no current at the output. This case was also verified in the laboratory. The only
complication was that the voltage output was allowed to range all the way up to 16.25-16.33 volts.
Although this is not exactly as we would have liked the output to behave, the result is not
unexpected. The variation in the output is due to the error of the zener diode. As the
manufacturer’s datasheet suggests the acceptable zener voltage can vary as much as 5 percent.
Given this specification this voltage is within the acceptable range.
The next case to be tested is an applied potential below 16 volts with reversed polarity input.
As expected, the result was a tripped circuit breaker and no current at the output. The last case was
to test a potential in excess of 16 volts with reverse polarity. In this case the result was also as we
expected, a tripped circuit breaker and no output current.
39
4.7.6 Schematics
Figure 5: High voltage protection schematic
Figure 6: Reverse polarity protection schematic
40
Figure 7: Schematic for circuit protection
4.7.6.1 Component Value Selection
The circuit breaker CB1M was chosen on price alone. It is important that it’s value is above
the 1.1 Amps that our circuit could possibly draw, but 3 may be a little high. The diode D1M was
chosen to sustain the 3 amp current that would result in the reverse polarity condition. Diode D2M
needs no other consideration than its Zener voltage of 16 volts. The capacitor C1M’s value is not
crucial. 0.1uF is a good estimation of the value needed but anything with an order of magnitude
should work just as well. R1M was chosen to limit the amount of current that travels into the gate
of the SCR; its value is approximate and could change slightly without too much affect. The
SCRIM must be able to handle the 3 Amp current that is necessary to trip the circuit breaker.
4.7.7 Problems and Recommendations
The circuit shown above has been tested without incident. We believe its design is solid.
Any improvements would come in the way of cost reduction. For example the diode D1M must
only be able to handle the 3 Amps current for as long as it takes the circuit breaker to trip. It could
be possible to change the diode to one of a lower sustained current rating. One potential diode is
the 1N4001. At quantity this diode is about $0.05 cheaper than the one we currently use. This
could help to lower the price but should function just as the larger diode does in this case.
4.8 External On/Off Switch (User Interface)
4.8.1 Functions
The function of this module is to allow the user to manually switch power on and off from
the battery. This simple rocker switch has 2 positions. One position will connect the power supply
device to the battery and the other will disconnect the power supply device from the battery.
41
4.8.2 Inputs
The input to the switch will be at whatever DC potential the battery is currently operating.
This input could span a huge range of potential voltages. The current that can be expected into the
switch is less than 2 Amps but could be as high as allowed by the circuit breaker in the protection
circuitry, (3A).
4.8.3 Outputs
When the switch is in the closed/on position the output will be exactly the input. This is
neglecting any loss due to the minuscule amount of resistance the switch possesses. When the
switch is in the open/off position, no current will pass through the switch and the rest of the power
supply will be deactivated.
4.8.4 Component Value Selection
Any two position switch that can handle 3Amps would work in this module. We choose a
rocker switch for its smooth, positive action.
4.8.5 Problems and Recommendations
No problems have been discovered and no recommendations need to be made.
4.9 Complete Design
The schematic in figure 8 provides a complete view of our circuit design. This is the
schematic as implemented in the prototype. We have found that the modules work together as
designed and testing details of this integrated prototype are in section 5.5 of this document.
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Figure 8: Complete Power Supply Schematic
43
5 Results
5.1 Design Issues
Although we feel our design is solid, there are things which could be done better. In this
section we will give a brief overview of the design problems that have arisen. These problems are
explained in greater detail within the description of each module.
The first design weakness is the current regulation method used in the LED driver design.
Current regulation is preferable to voltage regulation for optimal LED performance. In order for
our LED driver module to utilize current regulation it was necessary to put a resistor in series with
the main projector LED and measure the voltage dropped across the resistor. This method is
effective at maintaining a constant current, however it is inefficient. In our design 700mW of
power is lost over this one resistor. This has the effect of bringing down our overall efficiency to 75
percent, a conservative estimate. This number is lower than we would like but could improve with
further development. We would also like to note that this efficiency is still better than what could
have been achieved with a linear design versus the switching regulator we have implemented.
A small problem with our design is the output current to the projector LED. The output is a
steady current, however it is not exactly the optimal 700mA that the projector LED’s datasheet
requests. Rather our output is about 640-650mA. This output is well within the manufacturer’s
acceptable range, however with minor tuning more optimal output could be achieved.
Another small problem is the value chosen for the circuit breaker. A 3 amp breaker was
chosen based upon price. Optimally we would like a breaker closer to the maximum value we
expect under normal circumstances. In our case we expect never to draw more that 1.5 amps from
the battery. We would like to have used a 1.5 or 2.0 rated circuit breaker. These devices do exist
but the cost seemed prohibitive to us and thus they were not used. Potentially there are some
improvements to be made by lowering the rating on the circuit breaker. This would allow the
current ratings on many of the other devices to be lowered as well. This is one area that deserves
further review.
Overall we feel our design is thorough and effective. We believe that if these problems are
addressed than the power supply design will be greatly improved. These suggestions should allow
the next phase of development to hone in on the key areas for improvement and bring the power
supply to realization within the Kinkajou.
5.2 Meeting Requirements
5.2.1 Customer Requirements
After the market research was complete we were left with a list of customer requirements for
our device. This is the rule book by which our design must be judged. In this section we will co
44
through the list of customer requirements commenting on the Team’s status as it relates to each
requirement.
The first customer requirement was that the design be inexpensive. For the most part we
believe we have achieved this goal. The component cost of our design has been reduced to $6.00 at
quantities of 1000 units. We believe this is within an acceptable range for cost. Of course the goal
was to get the design as in expensive as possible, but we believe our power supply is a good value
for the range of features it provides.
Another customer requirement was for the device to function in the Mali climate. We
believe there is no reason why our design would function any differently in Mali that it does in
Worcester. Issues of heat production have been addressed and we believe our design will do well
under any climate extremes.
The third customer requirement was for the device to last as long as possible before repair.
This requirement can not accurately be described as being met. The only way to test the reliability
of our device is to do some real world, long term testing.
The fourth customer requirement was for the design to take up little space so that it could be
easily incorporated into the design of the Kinkajou eventually. Our prototype has met the space
requirement well. The most bulky part of our project is the circuit breaker. The odd shape of the
device made it difficult to incorporate into the packaging of the prototype. Thus the prototype is
larger than it might otherwise have to be. Despite the large size of the prototype we believe this
requirement has been met.
Given our efficiency rating of 75 percent we believe we will be able to meet the next
customer requirement. Our research has shown that the customer would like the device to operate
for at least 3 hours before needing a battery recharge. Without knowing what specific battery we
are running off of it is impossible to make any realistic calculations as to the batteries run time. We
feel this requirement has been met, but only more exhaustive field testing will determine this with
any accuracy.
We believe our design does a good job to warn the user before the battery shuts down. Our
comparator circuit and low battery indication LED gives ample warning that the battery is low. We
also feel that this single LED system is the most affective way to indicate a low battery condition to
the user.
Our power supply will certainly output a constant strong brightness for the LED over the
whole operating time. There are no issues of light intensity step changes as the input voltage
changes to the device. As mentioned in the design issues the output could be optimized to some
degree, but none the less the requirement has been met.
Our design runs the fan at the constant full power that is allowed by the battery state at the
time. The fan driver does not regulate the voltage to the fan rather it runs the fan at the maximum
power for the current input condition. We believe this design should do well the keep the system
45
cool. If the heatsink has been sized correctly and the other mechanical issues have been addressed
than out fan should keep the protector cool without any problems.
Our battery protection circuit keeps the battery safe. By keeping the operating range above
10.8 volts we believe we will eliminate any damage to the battery. This requirement may require
further testing in order to be verified, but we believe the requirement has been met.
The requirement that the device be easy to repair is a difficult one to judge. We believe our
design is simple and obvious enough. However we realize that this is a subjective judgment. We
have no idea how difficult it would be for a technician in Mali to get a replacement switching
regulator should one go bad. These are questions that do not have simple answers making this
requirement a tough call.
We believe our design is very simple to operate. The user interface has been minimized to
every extent possible. Under normal operation the only thing the user needs to worry about are the
main power switch, the low battery indication light and the circuit breaker reset. This makes
operation simple and painless to the user.
Our design is safe. There are not large hazards that the operator of the device faces. It
would be difficult to injure yourself while operating our power supply.
In summary we feel most of our customer requirements can safely be labeled as met. The
rest of the requirements require more testing in order to be sure. We are confident that this further
testing will show our design has satisfied every one of the design requirements.
5.2.2 Product Specifications
Specifications Met:
• Accept 12V Lead-Acid Car battery input (10.5-16V)
• Provide 110mA DC at 12V to fan
• Provide warning output to the user before shut-off occurs
• Turn off automatically before battery is run beyond rechargeability (10.5V)
• On/off switch
• Have casing to protect device from humidity and dust (until it is incorporated into the
Kinkajou package)
• Connections within driver circuit should be durable
• Connections to input and output should be durable
• Should not weigh more than 1lb. (lighter is better)
• Should not take up more than 1,000 cm3 (smaller is better)
46
Needs Improvement:
• Minimize power consumption
• Provide consistent DC current of 700mA to LED for a minimum of 3 hours
• Use inexpensive, readily available, durable components and casing
• Use a minimum number of parts
• Graphical or French labels for on/off and low battery indicator
Needs More Testing:
• Function in humidity and temperature of Mali:
Temperature 11ºC - 42ºC
Humidity 28.3% - 80.5%
5.3 Cost Analysis
The component cost of our design has been reduced to $6 at quantities of 1000 units. This
includes all the necessary parts and pieces to build our design and place it within the Kinkajou.
Cost of some packaging has been left out of this figure. Things such as the prototype casing, which
would not be included in the final design, have been eliminated form this cost consideration. As
previously stated, this $6 figure does include every component that would be necessary to connect
the power supply to the battery and power the projector LED and fan.
The cost to manufacture the power supply should be in the neighbor hood of $4-6. This
generous margin should be more than enough to cover the cost to manufacture the device. These
figures are based on very rough estimates. We have designed this device such that it requires a
minimum of labor. A printed circuit board would need to be designed and manufactured. Then the
components would need to be soldered in place. More accurate manufacture cost must be
determined.
The per-unit cost of each piece is in the range of $10-12 for the sum of parts and
manufacturing cost. In order to ensure a reasonable return on any initial investment a generous
profit must be included in the projected sale price. For our case we will assume that the profit
margin could range from 50% to 100% of the product cost. The sale price of the item should fall
between $15-25.
While the component cost is within range, the overall cost seems too high. Although the
team has spend some time trying to bring the cost of the components down, we are confident some
more could be cut here. The most expensive component was the circuit breaker, which accounts for
1/5 of the total component cost. We feel that the protection added by this component and its
usability make this cost worthwhile. Although this figure is high, we believe that our design meets
the requirement of being inexpensive. The substantial padding that has been added to the cost
figures will surely come down if more accurate cost analysis is done.
47
5.4 Competitive Value Analysis
There are a number of different products currently available to power a 5 Watt LED. We
know that there is a market for our product, but we must determine how our product stacks up
against those currently on the market. We can apply our value ratings to our competitors and our
own product (Appendix B).
5.4.1 Competitors
There are a number of manufacturers which have LED drivers on the market. More
specifically there exist a number of power supplies designed specifically to power the Lumileds 5
Watt LED. For this section we will consider these products as our direct competition. Not all
products do all of what is asked by our customers, however the products are similar enough to be
considered competition.
5.4.1.1 Analog Technologies, Inc.
The first competitor to our product is produced by Analog Technologies. High Efficiency
LED Controller (LED22V1A-700MA) is designed to power one 5 Watt Luxeon LED. This power
supply does not have the capability of powering a fan as well.
Criterion
Score
Efficiency
3
Cost
x
Longevity
0
Serviceability
0
Size
5
Durability
2
Fan Performance
0
LED Performance 5
Battery Protection 1
Performance
Low
Battery 0
Indicator
Usability
5
(Analog Technologies 2003)
Notes
90% typical
$9.50 per 1000
no claims about life span are made
not serviceable
very small
no mention of ability to withstand elements
no fan driver
driver should power LED flawlessly
shutdown voltage is too low
no indicator
no interface
5.4.1.2 LED Dynamics
The second competitor to our product is the PowerPuck produced by LED Dynamics. Their
12VDC 5W LED Drive Module (2008) is designed to power one 5 Watt Luxeon, 4 one Watt
Luxeon, or strings of 5mm LEDs. This power supply does not have the capability of powering a
fan as well.
48
Criterion
Efficiency
Cost
Longevity
Serviceability
Size
Durability
Fan Performance
LED Performance
Battery Protection
Performance
Low
Battery
Indicator
Usability
(LED Supply 2003)
Score
2
x
3
2
3
4
0
5
1
Notes
76% to 86% range, 82% typical
$18.00
life span is said to be as long as the LED
epoxy coating would make service difficult
very small
packaging looks sturdy and weather tight
no fan driver
driver should power LED flawlessly
shutdown voltage is too low
0
no indicator
5
no interface
5.4.1.3 The Luxeon LED Project
The third competitor of ours is the 5 Watt Driver produced by the Luxeon LED Project.
This is designed to power one 5 Watt Luxeon and nothing else.
Criterion
Score
Efficiency
2
Cost
x
Longevity
2
Serviceability
5
Size
4
Durability
4
Fan Performance
0
LED Performance 5
Battery Protection 1
Performance
Low
Battery 0
Indicator
Usability
5
(The LED Project 2003)
Notes
75% to 90% range, 85% typical
on sale from 22.95 to $19.95
life span is inferred to be slightly less than the LED
relatively simple design with common parts
very small
no casing or any other protection, just a board
no fan driver
driver should power LED flawlessly
shutdown voltage is too low
no indicator
no interface
5.4.2 Our Power Supply
This section details the results we can expect from our power supply. As per the results
listed in section 3, it became clear to us that some compromises must be made. Cost was the most
significant factor in our design; therefore it limited the features that we could include in our product.
For example the auto shutoff capabilities and the temperature sensitive fan feature could not be
included for this reason. However, we believe that the design detailed below represents the best fit
49
to the customers needs. A complete comparison of our design to our competitors can be found in
Appendix D.
WPI EE2799 Project Team 8
Criterion
Efficiency
Score
3
Cost
Longevity
Serviceability
x
3
4
Size
Durability
Fan Performance
LED Performance
3
3
5
4
Battery Protection 4
Performance
Low Battery
4
Indicator
Usability
4
Notes
We expect our design to have a run time of at least 3 hours, but we
suspect it to last a lot longer. Calculated power efficiency is 75%
at a very conservative estimate.
Projected cost is below $6.
We expect our design to last as long as the LED.
The design allows for replacement of discrete components with
relative ease.
Replacement parts are available from the
manufacturer.
The size could decrease for mass production.
Further testing is necessary to accurately asses this.
Sufficient power is delivered to the fan for continuous operation.
The device produces a constant current of about 650mA. Further
testing is required to determine exact performance at this current.
This design could be easily modified to improve performance.
The battery is shut-down before being depleted too low. Margins
of error in the components make this less than perfectly exact.
We have an indicator and automatic shutdown fully functioning.
Margins of error in the components make this less than perfectly
exact.
Product is easy to use and requires little of the user.
5.4.3 Conclusion
Analysis of our product’s competitors helped to highlight the strengths and weaknesses of
each. These criteria were than applied to our product in order to determine how our power supply
stacks up. After analyzing three potential competitors for our product, we have determined that
there is a need for our product in the market. Two of the three products we examined far exceeded
our cost goal of 10% of the cost of the Kinkajou projector. None of the potential competitors
provide a second output suitable for powering a cooling fan. One of the strengths of our
competitors is a very small size. Size, however, does not outweigh performance and cost. Also,
none of the products provide robust battery protection. It seems that our toughest competitor will be
Analog Technologies, which has a low-cost, high performing product. However, none of the
competitors we analyzed were able to meet the customer requirements for the Kinkajou projector.
We feel our design provides the best option to satisfy these requirements. This analysis used
conservative estimates of our product, and we hope to far exceed them, producing an even more
competitive device. A more complete comparison strengths and weaknesses can been found in the
value analysis table included in the Appendix D.
50
5.5 Testing
Testing of our power supply is incomplete at this point. Short duration testing on the order
of 20 minutes has been done, but it is necessary to complete long term testing. Additionally our
design has yet to see any environments similar to its operating environment. All testing has been
completed within a laboratory setting which does not necessarily reflect how the product will
operate in the field. No testing has been done with an actual car battery or the actual projector.
Appendix F details our testing to date. There are some important things to note about this
data. First this testing was completed and all measurements were taken without the fan in place.
This was done because we did not have access to the correct fan. Rather than throw off our
readings by using an incorrect fan, we decided not to include the fan for our quantitative analysis.
We did connect a similar fan in parallel to confirm proper operation. With this in mind our power
consumption calculations include only a theoretical power consumption by the fan. However,
because of the nature of our fan drivers design this should not effect the efficiency calculations of
our product. We assume there will be no power loss in our device as it is delivered to the fan.
To get a perspective on the accuracy of our measurements we have included the equipment
that we have used in the laboratory testing. Hopefully this information will help any future
engineers understand our results better by helping them put our numbers in perspective with their
own. All laboratory testing was performed using the following equipment:
GW Digital Multimeter
GW instek Laboratory DC Power Supply
Model: GDM-8034
Model: GPS-3303
Testing has shown that our power supply delivers a constant current to the LED as we
expect. Measurements were taken over the full operating range to ensure our results were as
expected. As our data shows, some of the measurements have been calculated and not measured
directly with the test equipment. This is a result of limitations placed upon us by the test
equipment.
51
6 Next Steps and Recommendations
We feel that there a few important steps that should be taken in order to enhance and verify
this design. Sections 4 and 5.1 explain these design issues in more detail.
1. More thorough testing of this product is still required. Verification is needed to confirm that
this power supply runs the Kinkajou LED at a constant brightness and runs the fan for
sufficient cooling of the Kinkajou. We have modeled the Kinkajou LED as a 10 Ohm
resistor, but did not have access to the Luxeon 5W White LED for testing. Our product
needs to function in the climate of Mali, so it should be tested for sustained operation and
heat dissipation at temperatures ranging from 11ºC to 42ºC, (Geography IQ 2003), and
humidity of 28.3% to 80.5%, (United Nations Environment Programme 2003).
2. Through our own testing, we have determined that the two transistors get quite hot, which
we did not predict. Heat analysis and a heat sink will be needed.
3. For this prototype, we decided to use a big package because it is manipulated easily. Other
electrical engineers can look at other package options. If our product laid out strategically, it
will fit into the Kinkajou projector. To reduce size even more, surface mount components
could be used, though this may make repairs more difficult. Mechanical engineers will have
to redesign the projector to fit our product into the projector.
4. More research about cheaper components could bring down the cost. However, cost needs
to be weighed against the durability of the components.
5. We recommend replacing the current voltage regulator component with a voltage reference
that has a smaller margin of error and more accurate resistors to improve the effectiveness of
the battery protection functions.
6. The LED driver could be made more accurate by using a more precise current sense resistor,
and efficiency could be improved by analyzing alternative feedback methods.
We believe we have achieved a high level of progress in our design of the Kinkajou power
supply. We recommend that our design be further analyzed and developed in order to achieve the
performance desired by Design That Matters, our client.
52
7 References
Analog Technologies, Inc., High Efficiency LED Controller, 28 April 2003.
http://www.analogtechnologies.com (28 October 2003)
All Electronics Corp, Parts Search, <http://www.allelectronics.com/> (9 November 2003)
Bigelow, Ken, The Silicon Controlled Rectifier, <http://www.play-hookey.com/semiconductors/
scr.html> (22 November 2003)
Central Intelligence Agency, The World Factbook (online), 1 August 2003,
<http://www.cia.gov/cia/publications/factbook/geos/ml.html> (29 October 2003)
Coleman, Lighting, 2002,
<http://www.coleman.com/coleman/ColemanCom/category_main.asp?CategoryID=1000>
(12 December, 2003)
Digi-key, LM3578AN-ND, <http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail?
Ref=211624&Row=245215&Site=US> (2 December 2003)
Digi-Key Corporation, Parts Search, < http://www.digikey.com/> (9 November 2003)
Fairchild Semiconductor, 1N5818 Datasheet, 2001
<http://www.fairchildsemi.com/ds/1N/1N5818.pdf> (17 December 2003)
Geography IQ, <http://www.geographyiq.com/> (31 October 2003)
Good Sam Club, Why join the Good Sam Club? <http://www.goodsamclub.com/non1a.cfm>
( 31 October 2003)
Jameco Electronics, Parts Search, < http://www.jameco.com/> (9 November 2003)
Lite-On Technology Corporation, LTL307E Datasheet, 2003
<http://www.liteon.com.tw/OPTO/SPEC/DATABOOK.NSF/PASN/DS-20-920159/$file/307E.pdf> (23 November 2003)
LED Supply, PowerPuck 12V 5W 700mA LED Drive Module,
http://www.ledsupply.com/02008a.html (30 October 2003)
The LED Project, The LED Project Main Page, <http://www.geocities.com/george_tlc/led.html>
(9 November 2003)
Lumileds, Luxeon V Portable Technical Data DS40, October 2002,
<http://lumileds.com/check.cfm?file=DS40.PDF> (22 November 2003)
53
Marktech Optoelectronics, MT305 Datasheet, January 28, 2002
<http://www.marktechopto.com/PDFs/Marktech/Low_Current_5mm_LEDs_020128.pdf>
(3 December 2003)
Microchip, <http://microchip.com/> (11 November 2003)
Mouser Electronics, Parts Search, <http://www.mouser.com/> (9 November 2003)
National Semiconductor, LM3578A Datasheet, 1998,
<http://www.national.com/ds/LM/LM1578A.pdf> (23 November 2003)
National Semiconductor, LM358 Datasheet, March 2002
<http://www.national.com/ds/LM/LM158.pdf> (23 November 2003)
National Semiconductor, LM78L05 Datasheet, May 2003,
<http://www.national.com/ds/LM/LM78L05.pdf> (23 November 2003)
Panasonic, Sealed Lead-Acid Batteries Technical Handbook 2000, January 2000,
<http://www.battery-service.de/daten/bleiakku.pdf> (17 December 2003)
Philips Semiconductors, Products Data Handbook System
<http://www.semiconductors.philips.com/pip/P82CF201BDH.html> (9 November 2003)
Sunon, MagLev Fan, 2002, <http://www.sunon.com.tw/products/pdf/dc-fan/3maglev_kde.pdf>
(30 November 2003)
United Nations Environment Programme, “Mali-Bamako Summary Project Site,”
<http://www.unep.org/DEWA/water/groundwater/africa/English/reports/CountrySummaries
/Mali/Eng-Summary-Mali.pdf> (31 October 2003)
United States Patent and Trademark Office (USPTO), 27 August 2003,
<http://www.uspto.gov/patft/> (10 November 2003)
Vaz, Rick and Stephen Bitar, 5 November 2003,
<http://ece.wpi.edu/~vaz/courses/ee2799/b03/Labs/DtM/DtM5Nov.htm>
(23 November 2003)
Vaz, Rick and Stephen Bitar, “Project 2 — High Efficiency Kinkajou Power Supply”, 28 October
2003, <http://ece.wpi.edu/~vaz/courses/ee2799/b03/Labs/kinkajou.htm> (30 October 2003)
The World Bank Group, World Development Indicators 2003 (online), August 2003,
<http://devdata.worldbank.org/external/CPProfile.asp?SelectedCountry=MLI&CCODE=M
LI&CNAME=Mali&PTYPE=CP> (29 October 2003)
Zetex, PNP Silicon Planar Medium Power Transistor Datasheet, April 1994,
<http://www.zetex.com/3.0/pdf/ZTX749.pdf> (1 December 2003)
54
Appendix A: Design Schedule
55
Appendix B: Value Ratings Explained
The following chart explains our method of assessing values for the various criteria used in the value
matrices.
Rating description
Score
Efficiency
Most efficient
Very efficient
Moderately efficient (expect 3 hours)
Somewhat inefficient
Very inefficient
Will not last long at all/unknown/unreliable
5
4
3
2
1
0
Cost
estimated cost for quantity of about 800
Feasibility of Design
It is already done (plug and play)
We already know how to do it
We have a good idea of how to do it
We would need to do a lot of research
We do not know anything about it
We cannot do it
5
4
3
2
1
0
Longevity
We expect this to last twice as long as the LED
5
We expect this to last one and a half times longer than the LED 4
We expect this to last as long as the LED
3
We expect this to last nearly as the LED
2
Lasts half the life of the LED
1
Lasts less than half the life of the LED /unknown/unreliable/fragile 0
Size
Less than 1 cubic inch
1-2 cubic inches
2-3 cubic inches
3-4 cubic inches
4-5 cubic inches
Greater than 5 cubic inches
5
4
3
2
1
0
56
Performance
Does everything perfectly
Does most things very well
Does some things well
Does not do things well
Meets requirements poorly
Does not meet requirements
5
4
3
2
1
0
Usability
Nothing for the user to do/ very pleasant
Perfectly intuitive/ no technical knowledge needed/ requires occasional user intervention/ pleasant
Somewhat intuitive/ technical knowledge helps/ requires user intervention/ indifferent
Not intuitive/ requires technical knowledge/ requires repeated user intervention/ not pleasant
Hard to use/ requires extensive technical knowledge/ unpleasant
Unusable
5
4
3
2
1
0
Serviceability
Replacement parts are readily available (in Mali)
Replacement parts are available through manufacturer
Packaging allows easy service
Packaging hampers serviceability
Replacement parts scarce
Unserviceable
5
4
3
2
1
0
Durability
Product is completely environment proof
Product is waterproof
Product is water resistant
Product is enclosed in a protective casing
Product has no casing, but some other protective measures
Product has no discernable protection
5
4
3
2
1
0
57
Appendix C: Parts for Value Analysis Estimates
Please note that these are NOT the parts used for our prototype, but rather the parts we examined
when making our design decisions.
Purpose
Battery
Indicator
Battery
Indicator
Battery
Indicator
Battery
Indicator
Battery
Indicator
Battery
Indicator
Battery
Indicator
Battery
Indicator
Battery
Protection
Battery
Protection
Battery
Protection
Battery
Protection
Battery
Protection
Pulsing
LED
Pulsing
LED
Pulsing
LED
Pulsing
LED
Pulsing
LED
Pulsing
LED
Component
Manufacturer
Price
Part
Source (URL/Catalog)
LED
Ligitek
0.07
LE3330
http://www.jameco.com/
LED
Vibrating
Indicator
Vibrating
Indicator
Ligitek
0.07
LVG2043
http://www.jameco.com/
Panasonic
2.99
KHN4NB1N
http://www.digikey.com/
Panasonic
2.99
http://www.digikey.com/
LCD
Lumex
4.94
KHN5NB1AA
LCMS01601DTR
http://www.mouser.com/
LCD
Lumex
2.98
LCD-S101D14TR
http://www.mouser.com/
Speaker
Kobitone
1.05
.58 oz 253-4020
http://www.mouser.com/
Speaker
Kobitone
1.06
253-5133
http://www.mouser.com/
fuse
Various
0.12
http://www.allelectronics.com/
fuse holder
Various
0.5
http://www.allelectronics.com/
diode
TAITRON
0.25
relay
circuit
breaker
Various
0.5
http://www.allelectronics.com/
Various
0.5
http://www.allelectronics.com/
5.6K resistor
Xicon
82K resistor
Xicon
30K resistor
TAITRONT6A05L
http://www.jameco.com/
291(271)5.6K/AP
http://www.mouser.com/
291(271)-82K/AP
http://www.mouser.com/
Xicon
0.006(Carbon)
0.012(Metal)
0.006(Carbon)
0.012(Metal)
0.006(Carbon)
0.012(Metal)
291(271)-30K/AP
http://www.mouser.com/
20pf cap
Xicon
0.032
140-100N2-200J
http://www.mouser.com/
220pf cap
390mH
inductor
Xicon
0.05
140-102P6-221K
http://www.mouser.com/
Fastron
0.093
434-22-391
http://www.mouser.com/
58
DCConverter
Analog
(Buck)
diode
TAITRON
0.25
TAITRONT6A05L
http://www.jameco.com/
DCConverter
Analog
(Buck)
1mH
inductor
Epoxy
0.29
CEC-102J
http://www.jameco.com/
DCConverter
Analog
(Buck)
1microFarad
cap
Panasonic
0.09
(A1/50)
http://www.jameco.com/
DCConverter
Analog
(Buck)
10 resistor
Xicon
0.006(Carbon)
0.012(Metal)
291-10
http://www.mouser.com/
DC-DC
Converter
DC-DC IC
3.55
AA9090A
http://www.jameco.com/
59
Appendix D: Competitive Value Analysis Table
Competition vs. WPI
Value Analysis
Market Analog Tech
Quality
1 Efficiency
2 Performance (LED)
3 Performance (Fan)
4 Performance (Protect battery)
5 Performance (Battery status)
6 Durability
7 Longevity
Value point
60
40
40
40
40
75
75
Value point
3
5
0
1
0
2
3
Total
LED Dynamics
Total Value point
180
200
0
40
0
150
225
795
Market Analog Tech
Convenience
1 Usability
2 Size
4 Serviceability
Total
120
200
0
40
0
300
225
885
2
5
0
1
0
0
2
LED Dynamics
WPI Team 8
Total Value point
120
200
0
40
0
0
150
510
The Luxeon Driver
3
4
4
4
4
3
3
Total
180
160
160
160
160
225
225
1270
WPI Team 8
Value point
Total
Value point
Total
Value point
Total
Value point
Total
25
10
10
5
5
0
125
50
0
175
5
3
2
125
30
20
175
5
4
5
125
40
50
215
4
3
4
100
30
40
170
Market Analog Tech
Customer Value: (Quality*Convenience/Cost)
Value point
Value point
Total
Cost
1 Initial Cost
2 Replacement Parts
2
5
0
1
0
4
3
The Luxeon Driver
Total
LED Dynamics
The Luxeon Driver
WPI Team 8
Value point
Value point
Total
Value point
Total
Value point
Total
Value point
Total
100
100
9.5
0
950
0
950
18
0
1800
0
1800
19.95
0
1995
0
1995
6
0
600
0
600
146.4
86
60
55
359.8
Appendix E: Parts List for Prototype
Produc
t cost
(800)
Produc
t cost
(1600)
$0.40
$0.077
$0.060
1
$0.40
$0.120
$0.093
Digi-key
1
$0.20
$0.120
$0.105
Part description
Manufacturer Part
Number
C2
CAP .01UF 50V 10% CER
RADIAL
CAP .33UF 50V 20% CER
RADIAL
C317C103K5R5C
A
C322C334M5U5C
A
LED1
Red LED
SSL-LX5093XIC
Kemet
Lumex
Opto/
Component
s Inc.
R1
2K Ohm 1/4W Resistor - 5%
CFR-25JB-2K0
Yageo
2.0KQBK-ND
Digi-key
1
$0.10
$0.009
$0.009
R2
R3,
R5,
R9
13K Ohm 1/4W Resistor - 5%
CFR-25JB-13K
Yageo
13KQBK-ND
Digi-key
1
$0.10
$0.019
$0.009
10K Ohm 1/4W Resistor - 5%
CFR-25JB-10K
Yageo
10KQBK-ND
Digi-key
1
$0.10
$0.009
$0.009
R4
12K Ohm 1/4W Resistor - 5%
CFR-25JB-12K
Yageo
12KQBK-ND
Digi-key
1
$0.10
$0.019
$0.009
R6
1K Ohm 1/4W Resistor - 5%
CFR-25JB-1K1
Yageo
1.1KQBK-ND
Digi-key
1
$0.10
$0.009
$0.009
R8
510K Ohm 1/4W Resistor - 5%
CFR-25JB-510K
Yageo
510KQBK-ND
Digi-key
1
$0.10
$0.019
$0.009
U1A
Dual Low-Power Op Amp
LM358N
National
jameco
1
$0.40
$0.130
$0.110
Vreg
5V 100mA Voltage Regulator
CAP .1UF 50V 20% CER
RADIAL
LM78L05ACZ
C322C104M5U5C
A
Fairchild
23966
LM78L05ACZF
S-ND
Digi-key
1
$0.45
$0.149
$0.126
399-2171-ND
Digi-key
1
$0.40
$0.062
$0.048
Circuit Breaker
W28-XQ1A-3
Digi-key
1
$2.50
$1.326
$1.274
D1M
16v 1w zener diode
1N4745A-T
Digi-key
1
$0.36
$0.172
$0.076
D2M
3.3A diode
31DQ06
Diodes Inc
Internationa
l Rectifier
PB184-ND
1N4745ADICTND
31DQ06-ND
Digi-key
1
$0.58
$0.340
$0.229
R1M
1K Ohm 1/4W Resistor - 5%
CFR-25JB-1K1
Yageo
1.1KQBK-ND
Digi-key
1
$0.10
$0.009
$0.009
C1
C1M
CB1
M
Manufacture
r
Distributor part
number
Distributo
r
Kemet
399-2027-ND
Digi-key
1
399-2174-ND
Digi-key
67-1120-ND
Kemet
Tyco
Electronics
61
Qt
y
Prototyp
e Cost
Qty
Prototype
Cost
Product
cost
(800)
Product
cost
(1600)
Part description
Manufacturer Part Number
Manufacturer
Distributor
part number
Teccor
Electronics
S6006V-ND
Digi-key
1
$0.74
$0.429
$0.413
ZTX749-ND
PS1H182JND
P10397TBND
1326PHND
Digi-Key
2
$2.26
$0.752
$0.752
Digi-Key
1
$0.35
$0.253
$0.151
Digi-key
1
$0.90
$0.090
$0.090
Digi-key
2
$0.80
$0.082
$0.060
Digi-key
1
$0.50
$0.050
$0.038
Mouser
1
$0.12
$0.053
$0.051
Digi-key
1
$2.08
$0.952
$0.833
Digi-key
1
$0.16
$0.084
$0.062
Digi-key
1
$0.10
$0.009
$0.009
Digi-key
1
$0.10
$0.009
$0.009
Digi-key
1
$1.92
$0.806
$0.794
jameco
1
$0.29
$0.220
$0.220
Box
1
$3.00
Molex connectors
2
$1.50
$6.378
$5.664
SCR1M
Q1E,
Q1
SCR
S6006V
PNP Transistor 25V 2A
ZTX749
C1E
0.0018uF ceramic Capacitor
ECH-S1H182JZ
C2E
100uF Capacitor
ECA-1HM101B
C3E
10pF ceramic Capacitor 5%
D100D20C0GH63L6
C4E
10uF Capacitor
ECA-1HM100
D1E
Shottky Diode
1N5818
L1E
330uH, .95A-DC, 1.61A max
4590-334
R1E
1.5 OHM METAL FILM 1W 5%
5073NW1R500J12AFXBC
Rectron
API
Delevan,
Inc.
BC
Components
R2E
1.3K Ohm 1/4W Resistor - 5%
CFR-25JB-1K3
Yageo
R3E
2K Ohm 1/4W Resistor - 5%
CFR-25JB-2K0
Yageo
U1E
Switching regulator
LM3578AN
National
SW1M
switch quick disconnect rocker
52-6VBU
Zetex Inc.
Panasonic ECG
Panasonic ECG
BC
Components
Panasonic ECG
P980-ND
5831N5818-B
DN4518ND
BC1.5W1CT-ND
1.3KQBKND
2.0KQBKND
LM3578ANND
202497
Distributor
$21.21
62
Appendix F: Test Results
Readings from Laboratory Power Supply
Measurements taken with
Multimeter
Calculated
Results
Current In
(mA)
10.8
562
519
487
466
436
413
401
388
367
0
0
0
Voltage Out
to load (V)
0
6.59
6.6
6.62
6.62
6.62
6.64
6.64
6.65
6.65
0
0
0
Load Current
(mA)
0.000
652.475
653.465
655.446
655.446
655.446
657.426
657.426
658.416
658.416
0.000
0.000
0.000
Voltage In
(V)
11
11.6
12
12.5
13
13.5
14
14.5
15
15.5
16
16.5
17
Power In (W)
0.1188
6.5192
6.228
6.0875
6.058
5.886
5.782
5.8145
5.82
5.6885
0
0
0
Resistance of load
(Ohms)
10.1
10.1
10.1
10.1
10.1
10.1
10.1
10.1
10.1
10.1
10.1
10.1
10.1
Power Out
(W)
0.000
4.300
4.313
4.339
4.339
4.339
4.365
4.365
4.378
4.378
0.000
0.000
0.000
Efficiency
N/A
0.660
0.692
0.713
0.716
0.737
0.755
0.751
0.752
0.770
N/A
N/A
N/A
The load represents the Kinkajou LED and the fan was not connected for these tests. The Kinkajou LED is “off” for voltages in less
than 11V and greater than 16V.
63
Appendix G: Prototype Photos
64