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High efficiency HVAC blower motor control
Rev. 1 — 14 April 2016
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Document information
Info
Content
Keywords
HVAC, blower motor, linear mode, PWM mode, MOSFET, efficiency, CO2
emission
Abstract
This report introduces a high efficiency HVAC blower motor control
solution using PWM. It discusses the market information, CO2 emission,
power loss investigation and BOM comparison in detail.
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High efficiency HVAC blower motor control
Revision history
Rev
Date
Description
1.0
20160414
initial release
Contact information
For more information, please visit: http://www.nxp.com
For sales office addresses, please send an email to: salesaddresses@nxp.com
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1. Introduction
Heating, Ventilation, and Air Conditioning (HVAC) systems are increasingly being used in
modern vehicles to provide passenger comfort and maintain air quality in the cabin
environment.
In conventional HVAC systems, air is either drawn from outside the vehicle by suction and
blown into the cabin, or circulated within the vehicle itself. Usually a 250 W brushed DC
motor is used, with a MOSFET operated in linear mode. An additional 80 W to 150 W of
power is dissipated in the form of heat at the MOSFET. As a result, the MOSFET requires
a large heat sink to maintain a stable junction temperature. The drawbacks of this solution
are apparent: inefficiency due to high thermal power dissipation at the MOSFET,
sensitivity to the thermal path from MOSFET to heat sink, and increased weight and
system size. Together, it leads to a higher overall cost and CO2 emissions than alternative
solutions. As emission targets continue to fall, these drawbacks are becoming more
relevant to car OEMs, tier 1 and tier 2 suppliers.
This report provides an overview of the automotive HVAC systems, market and
environmental emissions considerations. It proposes a high efficiency solution using
MOSFETs operated in PWM mode.
2. HVAC system topologies
There are three types of HVAC control system namely: manual, semi-automatic, and fully
automatic HVAC system.
2.1 Manual HVAC system
Manual HVAC systems are basic, low-cost solutions enabling heating and cooling using
an open loop control method. Manual HVAC use resistor arrays to adjust the speed of the
blower motor; see Figure 1. Semiconductor devices are not used in these systems.
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Resistor arrays in manual HVAC system
2.2 Semi-automatic and fully automatic HVAC system
Semi-automatic HVAC systems allow some form of thermostatic control, usually with a
rotary switch and adopting a closed loop control method.
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Fully automatic HVAC systems are thermostatically controlled systems, where the driver
can select the required temperature, usually via a digital display. A fully automatic system
uses closed loop control method with environmental sensors.
Semi-automatic and fully automatic systems use MOSFETs to adjust the blower motor
speed. The MOSFET can be operated in either linear mode or Pulse Width Modulation
(PWM) mode to control motor speed.
2.2.1 MOSFET in linear mode
In linear mode, the MOSFET is operated in a partially enhanced state. The gate voltage
(VGS) is sufficient to draw the required current (IDS). A voltage (VDS) is supported across
the drain-source of the MOSFET, leading to potentially high-power dissipation during the
operation. The working of MOSFET in linear model is shown in Figure 2.
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The main advantage of this solution is that the gate drive circuit is simple and cheap.
Since the MOSFET is not switched, there is no switching noise (EMI) generated.
However, there are also significant disadvantages of this approach. When the blower
motor is working, an additional 100 W of power is dissipated in the MOSFET, on top of
motor losses. It leads to lower efficiency of the system, and increased sensitivity to the
mechanical assembly of the module. It also increases CO2 emissions for the vehicle.
2.2.2 MOSFET in PWM mode
The use of MOSFET in PWM mode improves the efficiency of the HVAC system and
helps to meet the new CO2 emissions standards. In a PWM solution, the MOSFETs are
continuously switched between their ON and OFF states to control the motor. Usually the
gate drive is set at a fixed frequency and variable duty cycle. Longer on-time (ton)
durations results in higher average load voltage, current and motor speed. Shorter ton
durations result in lower average load voltage, current, and motor speed. This control
approach complements the design of modern power MOSFET technology which has
excellent switching and on-state performance.
Automotive mechatronics PWM frequency is subsonic or ultrasonic (< 100 Hz or
> 20 kHz) to minimize acoustic noise and below 50 kHz for EMC reasons. The MOSFET
working in PWM mode is shown in Figure 3. Assume that the maximum work current is
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30 A and the on-state resistance of the MOSFET is 3.5 m. If we add the conduction loss
and switching loss together, the resultant power loss is not more than 8 W. Comparing it to
a power loss of 100 W in linear mode, it is a huge power saving of at least 92 W.
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3. Market assessment
According to data from strategy analytics, the global HVAC market is growing at
approximately 5 % year over year, in line with the vehicle production. The largest markets
for HVAC systems are in China, Europe, and North America; see Figure 7. However,
nearly 50 % of systems in the China region are manual, in which semiconductor devices
are not used; see Figure 6.
Semi-automatic systems account only for about 10 % of the market and are forecast to
remain relatively flat over the coming years.
Fully automatic HVAC has a large market penetration, and is forecast to increase share
over the coming years. Penetration of fully automatic HVAC is high in both Europe and
Japan, reflecting the maturity of these markets. Opportunities are present for
manufacturers in China and SAPAC, where manual systems prevail and there are still a
good proportion of vehicles without HVAC. For these regions, low-cost solutions are
desired. Hence, there is a large proportion of manual systems. In these regions fully
automatic systems often implement MOSFETs in linear mode rather than PWM, for the
reasons stated above. The PWM solution is nevertheless not new in this market.
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In Japan, PWM solutions are the preferred solutions for fully automatic HVAC modules. It
is because PWM follows a high technology approach, which has benefits such as
low-power dissipation and improved motor control. In addition, three-phase motor control
is also preferred to reduce the noise of HVAC module. Verband Der Automobilindustrie
(VDA) members have standardized the Blower Pulse Controller (BPC) using PWM
technology to contribute to the fuel efficiency of automotive. As suppliers continue to
diversify into other regions, we would expect to see more fully automatic systems,
employing PWM topologies in the future. It is in line with the advances in semiconductor
technology, where next generation MOSFETs have improved switching and on-state
efficiencies. PWM solutions exploit these features.
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HVAC system segmentation in the year 2015
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HVAC regional segmentation in the year 2015
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4. Environmental emission considerations
4.1 CO2 emission
The 2021 european emissions target for passenger vehicles is 9.5 kg CO2 per 100 km. It
results in a fuel consumption of 4.1 liter per 100 km1.
Every 100 W of electrical power dissipated in the vehicle consumes 0.1 liter per 100 km.
Similarly, adding a further 50 kg of mass to the vehicle consumes 0.15 liter per 100 km.
Translating it into carbon emissions, every 1 liter of fuel combusted per 100 km results in
2.35 kg of CO2 being emitted2. This data indicates that every 430 W of electrical power
dissipation results in additional 1 kg CO2 emitted per 100 km. It also indicates that a
weight of 142 kg added to a vehicle results in additional 1 kg CO2 emitted per 100 km.
For linear mode topology, maximum power is dissipated in the MOSFET when the blower
motor runs at medium speed. In PWM mode, maximum power is dissipated when the
blower motor is operated at high speed.
Since the maximum power for linear mode operation is 140 W and 10 W for PWM mode, it
is clear that PWM topology saves 130 W. It equates to a fuel saving of 0.13 liter per
100 km, or emission of 0.30 kg CO2 per 100 km.
Adopting PWM solutions for HVAC could make a significant contribution towards meeting
future CO2 emission targets for OEMs.
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CO2 emission relationship with weight and fuel consumption
5. HVAC application demonstrator with MOSFET in PWM mode
To illustrate the benefits of adopting high efficiency solutions for HVAC, NXP has created
an application demonstrator of a blower module with MOSFETs. The blower module is
connected in various topologies to replicate HVAC systems in the market.
A typical HVAC electronic module mainly comprises of a blower motor driving board
separated from a main HVAC control board; see Figure 9. The main HVAC control board
receives the input from various sensors monitoring the board temperature, sunlight, and
1.
Data from european commission, http://www.nxp.com/external/ec-co2
2.
Fuel consumption to CO2 emissions data comes from http://www.nxp.com/external/eia-co2
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water temperature. It also receives feedback about the blower motor speed, battery
voltage, and the driver command. Based on these inputs, the microcontroller generates
an output signal to control the loads such as flap motors, blower motor, LCD, and lights.
The blower motor module, which is independent of the main ECU, is normally mounted in
the air flue. A large fan is often used to provide additional cooling; see Figure 9.
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Block diagram of HVAC system
Based on our market survey, the design of the blower motor modules for semi-automatic
and fully automatic systems can be broken down further into three subgroups.
The first type is the lowest technology solution, in which the input command from main
board to blower motor board is linear voltage signal. It changes from 2.5 V to 7 V, and the
objective is to generate a command for speed control of the blower. In this case, the
MOSFET is continually operating in linear mode. Only temperature monitoring of the
MOSFET is mandatory. No other protection functions exist on the board. This kind of
module is normally installed on the low-end vehicles.
The second type increases the complexity of the system. In these systems, the input is a
linear voltage or PWM signal. The MOSFET is again operated in linear mode. However,
more protection functions such as overvoltage protection and current limiting features are
implemented to provide additional functionality.
The third type is a high technology solution. It uses a MOSFET in PWM mode. The
module is typically operated with 400 Hz PWM input command. It has full protection and
diagnosis functions such as error recognition, short-circuit recognition, heavy load
recognition, protection from overtemperature, overvoltage, and undervoltage charge
pump.
To reflect the typical solutions worldwide, NXP has designed three different types of
boards. They are:
• Linear input command board with MOSFET operating in linear mode
• PWM input command board with MOSFET operating in linear mode
• PWM input command board with MOSFET operating in PWM mode
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All these solutions are designed with basic protection functions like temperature
protection using NTC thermistor, overvoltage protection, and current limiting function.
The block diagram of demo boards is shown in Figure 10, Figure 11, and Figure 12. In the
first two boards, an NXP power MOSFET in TO-220 package, BUK7510-55AL is used to
drive the motor. This MOSFET was designed specifically to operate continuously in linear
mode. It is used in combination with an effective heat sink to maintain a steady junction
temperature.
In the third board, an NXP power MOSFET in LFPAK56 (power-SO8) package,
BUK7Y3R5-40E is used to drive the motor. The letter ‘Y’ in the product name denotes
LFPAK56 (power-SO8) footprint.
One of the key benefits of the LFPAK56 package is that it has a much smaller footprint
than equivalent DPAK. Moreover, it has comparable thermal performance through
package design and copper clip technology by NXP.
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6. Power loss investigation
6.1 Power loss on MOSFET in linear mode
When the MOSFET operates in linear mode, the blower motor and the MOSFET share
the battery voltage. When the blower motor is operated at high speeds, then the voltage
drop across the motor increases and the corresponding voltage across the MOSFET is
reduced. In this situation, a high current flows through both the blower motor and the
MOSFET.
The MOSFET characteristic data shown in Figure 13 is based on a real world linear mode
blower motor module. The characteristic graph is generated using LTspice simulator. The
battery voltage is 16 V and the ambient temperature is 25 C. In this module, the
maximum load current is limited to 30 A. Combining the current and voltage waveforms
during turn-on of the blower motor results in the power curve shown in Figure 14.
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Fig 14. Power dissipation on MOSFET in linear mode
In Figure 14, we can see that the highest power in the MOSFET occurs when the load
current is around 16 A. The corresponding power peaks at around 128 W. It is the
situation where the blower motor is at half speed. At maximum blower speed, the load
current is limited to 30 A, and the VDS is in the range of 2 V to 1 V. The flattening of the IDS
curve on the right-hand side exhibits the phenomenon; see Figure 14. In this region, the
corresponding power dissipation falls steeply from 36 W to 25 W. So, if the driver turns the
blower speed to maximum, then the losses are minimized. However, operation between
these limits results in significant power losses occurring at the MOSFET. The maximum
rated junction temperature for an automotive power MOSFET is typically 175 C. The
thermal resistance between junction and ambient should be 0.7 K/W for dissipating 128 W
power efficiently, and maintain the junction temperature below its rated maximum. Here,
the ambient temperature is assumed to be 85 C. It is a significant challenge and requires
a large heat sink with an excellent thermal interface with the MOSFET, often requiring
additional cooling through airflow.
6.2 Power loss on MOSFET in PWM mode
The following data is based on results from the BUK7Y3R5-40E which is a 40 V, 3.5 m
power MOSFET. As the current is directly related to the blower motor speed, it has the
same value as shown in linear mode operation. The MOSFET is operated using a 20 kHz
PWM gate control signal, and the slew rate is adjusted to balance switching power losses
and EMC performance. In the worst case of switching losses, 30 % of switching loss is
estimated. The power loss on the MOSFET corresponding to load current in PWM mode
is shown in Figure 15. When the blower motor is running at its highest speed, the power
on the MOSFET is around 8 W. It is also highest power on the MOSFET in the whole
operation.
Figure 16 shows the comparison of MOSFET power dissipation between linear mode and
PWM mode. Considering the user habits, people tend to operate the blower motor work at
high speed initially. It is to lower the temperature in the cabin, and then maintain a fixed
temperature. Therefore the motor current is in the region 15 A to 30 A during the initial
cooling period. The power dissipated in linear mode could be as high as 128 W during this
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time compared to 8 W for PWM mode. Adopting PWM operation would lead to a power
saving of 120 W. It leads to reduced fuel consumption and a further saving of 0.28 kg CO2
per 100 km.
As the temperature in the cabin reaches a comfort level, the blower is turned to lower
speed. But again, a saving of up to 100 W is realistic even in this period.
HVAC is one of the few applications within automotive electronics where linear mode
operation is still used. Most automotive electronic systems have now migrated to PWM
solutions, taking advantage of the performance, size and weight benefits of the advanced
semiconductor technologies. Taking a linear mode design approach always dictates that a
large semiconductor and heat sink are used to dissipate the 128 W power. As such, any
HVAC system following this path will be unable to take advantage of the trend towards
miniaturization in electronics in the future.
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7. BOM comparison
Based on the BOM list of HVAC demo, the cost of PWM solution is approximately 30 %
higher than the equivalent linear mode solution. It is in line with the market survey
information presented earlier. If we make a coarse estimate of the linear mode module
cost to be 5 $, then the corresponding PWM module becomes 6.5 $.
The power saved by adopting the PWM solution is 100 W on an average. The CO2
emission reduced is of the order of 0.24 kg CO2 per 100 km.
The CO2 emission and fuel exchange information is shown in Figure 8. For a fuel price of
50 $/bbl3, the additional cost incurred for using PWM solution is recovered after running
the car for just 119 km. Over the lifetime of the vehicle, the fuel saving could be as high as
350 liter.
8. Conclusion
There are several advantages in suppliers moving over to PWM solutions for HVAC. They
are:
• Significant performance, fuel and CO2 savings over the lifetime of the vehicle.
• As emission targets become more stringent, the contribution from smaller loads in the
vehicle become more relevant to car OEMs and tier 1 suppliers.
• Enables design flexibility and choice from semiconductor vendors.
• Potential for future performance and efficiency improvements based on the trend
towards miniaturization of electronic components.
• Improved reliability due to reduced power excursions and thermal cycling using PWM
switched MOSFETs, instead of high-power linear mode operation. High-power linear
mode operation requires excellent heat sinking and dedicated fans to maintain
junction temperature below the maximum rated value.
• There is an established long-term roadmap for PWM solutions, compared to legacy
solutions. The legacy solutions use mature technologies, with little scope for reduction
in cost. It is due to the fundamental need for large silicon die, with large heat sink
components that dissipates heat and power.
• PWM solutions can also take an advantage of emerging packaging technologies for
MOSFETs such as LFPAK56 power-SO8 from NXP, small footprint, and high
performance package.
The trend towards PWM solutions for motor drive applications such as HVAC blower
motor drive continues. It is concluded from the research presented in this article and
global CO2 emission restrictions.
3.
http://www.nxp.com/external/nasdaq-oil
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9. Abbreviations
Table 1.
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Abbreviations
Acronym
Description
BOM
Bill Of Materials
BPC
Blower Pulse Controller
CO2
Carbon dioxide
DC
Direct Current
ECU
Engine Control Unit
EMC
ElectroMagnetic Compatibility
EMI
ElectroMagnetic Interference
EU
EUrope
HVAC
Heating, Ventilation, and Air Conditioning
LCD
Liquid Crystal Display
MOSFET
Metal-Oxide Semiconductor Field-Effect Transistor
NA
North America
NTC
Negative Temperature Coefficient
OEM
Original Equipment Manufacturer
PWM
Pulse Width Modulation
ROW
Rest Of the World
SAPAC
South Asia PACific
VDA
Verband Der Automobilindustrie
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10. Legal information
10.1 Definitions
Draft — The document is a draft version only. The content is still under
internal review and subject to formal approval, which may result in
modifications or additions. NXP Semiconductors does not give any
representations or warranties as to the accuracy or completeness of
information included herein and shall have no liability for the consequences of
use of such information.
10.2 Disclaimers
Limited warranty and liability — Information in this document is believed to
be accurate and reliable. However, NXP Semiconductors does not give any
representations or warranties, expressed or implied, as to the accuracy or
completeness of such information and shall have no liability for the
consequences of use of such information. NXP Semiconductors takes no
responsibility for the content in this document if provided by an information
source outside of NXP Semiconductors.
In no event shall NXP Semiconductors be liable for any indirect, incidental,
punitive, special or consequential damages (including - without limitation - lost
profits, lost savings, business interruption, costs related to the removal or
replacement of any products or rework charges) whether or not such
damages are based on tort (including negligence), warranty, breach of
contract or any other legal theory.
Notwithstanding any damages that customer might incur for any reason
whatsoever, NXP Semiconductors’ aggregate and cumulative liability towards
customer for the products described herein shall be limited in accordance
with the Terms and conditions of commercial sale of NXP Semiconductors.
Right to make changes — NXP Semiconductors reserves the right to make
changes to information published in this document, including without
limitation specifications and product descriptions, at any time and without
notice. This document supersedes and replaces all information supplied prior
to the publication hereof.
Suitability for use — NXP Semiconductors products are not designed,
authorized or warranted to be suitable for use in life support, life-critical or
safety-critical systems or equipment, nor in applications where failure or
malfunction of an NXP Semiconductors product can reasonably be expected
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to result in personal injury, death or severe property or environmental
damage. NXP Semiconductors and its suppliers accept no liability for
inclusion and/or use of NXP Semiconductors products in such equipment or
applications and therefore such inclusion and/or use is at the customer’s own
risk.
Applications — Applications that are described herein for any of these
products are for illustrative purposes only. NXP Semiconductors makes no
representation or warranty that such applications will be suitable for the
specified use without further testing or modification.
Customers are responsible for the design and operation of their applications
and products using NXP Semiconductors products, and NXP Semiconductors
accepts no liability for any assistance with applications or customer product
design. It is customer’s sole responsibility to determine whether the NXP
Semiconductors product is suitable and fit for the customer’s applications and
products planned, as well as for the planned application and use of
customer’s third party customer(s). Customers should provide appropriate
design and operating safeguards to minimize the risks associated with their
applications and products.
NXP Semiconductors does not accept any liability related to any default,
damage, costs or problem which is based on any weakness or default in the
customer’s applications or products, or the application or use by customer’s
third party customer(s). Customer is responsible for doing all necessary
testing for the customer’s applications and products using NXP
Semiconductors products in order to avoid a default of the applications and
the products or of the application or use by customer’s third party
customer(s). NXP does not accept any liability in this respect.
Export control — This document as well as the item(s) described herein
may be subject to export control regulations. Export might require a prior
authorization from competent authorities.
Translations — A non-English (translated) version of a document is for
reference only. The English version shall prevail in case of any discrepancy
between the translated and English versions.
10.3 Trademarks
Notice: All referenced brands, product names, service names and trademarks
are the property of their respective owners.
All information provided in this document is subject to legal disclaimers.
Rev. 1 — 14 April 2016
© NXP Semiconductors N.V. 2016. All rights reserved.
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11. Tables
Table 1.
Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . .16
12. Figures
Fig 1.
Fig 2.
Fig 3.
Fig 4.
Fig 5.
Fig 6.
Fig 7.
Fig 8.
Fig 9.
Fig 10.
Fig 11.
Fig 12.
Fig 13.
Fig 14.
Fig 15.
Fig 16.
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Resistor arrays in manual HVAC system . . . . . . . .3
MOSFET operating in linear mode . . . . . . . . . . . .4
MOSFET works in PWM mode . . . . . . . . . . . . . . .5
Global growth of HVAC systems . . . . . . . . . . . . . .6
HVAC system segmentation in the year 2015 . . . .6
Regional penetration of HVAC systems in the
year 2015 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
HVAC regional segmentation in the year 2015 . . .7
CO2 emission relationship with weight and fuel
consumption . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Block diagram of HVAC system . . . . . . . . . . . . . . .9
Demo board 1 - linear input and linear mode. . . .10
Demo board 2 - PWM input and linear mode. . . . 11
Demo board 3 - PWM input and PWM mode. . . . 11
IV curve of MOSFET operated in linear mode . . .12
Power dissipation on MOSFET in linear mode . .13
Power dissipation on MOSFET in PWM mode . .14
Power dissipation comparison . . . . . . . . . . . . . . .14
All information provided in this document is subject to legal disclaimers.
Rev. 1 — 14 April 2016
© NXP Semiconductors N.V. 2016. All rights reserved.
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13. Contents
1
2
2.1
2.2
2.2.1
2.2.2
3
4
4.1
5
6
6.1
6.2
7
8
9
10
10.1
10.2
10.3
11
12
13
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
HVAC system topologies . . . . . . . . . . . . . . . . . 3
Manual HVAC system. . . . . . . . . . . . . . . . . . . . 3
Semi-automatic and fully automatic HVAC
system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
MOSFET in linear mode . . . . . . . . . . . . . . . . . . 4
MOSFET in PWM mode . . . . . . . . . . . . . . . . . . 4
Market assessment . . . . . . . . . . . . . . . . . . . . . . 5
Environmental emission considerations. . . . . 8
CO2 emission . . . . . . . . . . . . . . . . . . . . . . . . . . 8
HVAC application demonstrator with MOSFET
in PWM mode . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Power loss investigation. . . . . . . . . . . . . . . . . 12
Power loss on MOSFET in linear mode . . . . . 12
Power loss on MOSFET in PWM mode . . . . . 13
BOM comparison . . . . . . . . . . . . . . . . . . . . . . . 15
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Legal information. . . . . . . . . . . . . . . . . . . . . . . 17
Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Disclaimers . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Trademarks. . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Please be aware that important notices concerning this document and the product(s)
described herein, have been included in section ‘Legal information’.
© NXP Semiconductors N.V. 2016.
All rights reserved.
For more information, please visit: http://www.nxp.com
For sales office addresses, please send an email to: salesaddresses@nxp.com
Date of release: 14 April 2016
Document identifier: R_10067