“I hereby declare that I have read this thesis and in my opinion this thesis is
sufficient in terms of scope and quality for the award of the degree of Bachelor of
Engineering (Electrical-Electronics)”
Signature
:
....................................................
Name of Supervisor :
PN ISMAWATI BT ABDUL GHANI
Date
21 JUNE 2013
:
WIRELESS CHARGER
NURUL AIN BINTI MOHAMMAD
A thesis submitted in fulfillment of the
requirements for the award of the degree of
Bachelor of Engineering (Electrical-Electronic)
Faculty of Electrical Engineering
Universiti Teknologi Malaysia
JUNE 2013
ii
I declare that this thesis entitled “Wireless Charger” is the result of my own
research except as cited in the references. The thesis has not been accepted for any
degree and is not concurrently submitted in candidature of any other degree.
Signature
:
………………………………….
Name
:
NURUL AIN BINTI MOHAMMAD
Date
:
21 JUNE 2013
iii
Specially dedicated to my beloved parents, Salbiah bte Kasim and Mohammad bin
Rahim, siblings, lecturers and friends who had encouraged, guided and inspired me
throughout my four years of study in University Technology of Malaysia
iv
ACKNOWLEDGEMENT
On the submission project report on Wireless Charger I would like to extend
gratefulness towards Almighty Allah for allow the completion of this project. I also
would like to express gratitude and sincere thanks to supervisor Mrs Ismawati bt
Abdul Ghani, Senior Lecturer, Faculty of Electrical Engineering, for constant
motivation and support during the course of work for two semesters.
I truly
appreciate and value her esteemed guidance and encouragement from the beginning
to the end of this project.
I would also like to express gratitude towards, Assc Prof Dr Rubita bt
Sudirman and Assoc. Prof. Dr. Awang bin Jusoh, for the various advices and
information that they gave for development of the project. My friends should also be
recognized for their support and help through the completion of this project. Their
helps and views have helped me a lot.
Unfortunately, it is not possible to list all of them in this limited space. I am
grateful to all my family members for their endless support throughout my study.
v
ABSTRACTS
Today‟s technology is growing faster and all electrical devices are becoming
simpler to handle. People also love to change the gadget as technology developing
without care of the prices. Wireless product became hot item because it is simple to
use and as a sign of high technology. It also will solve the tangle wire problems that
will cause accidents. This project idea came from that situation and wireless charger
is the decided for the project. It was built using magnetic induction coupled process
and concept. The self-build inductor will be connected to transmitter and receiver
circuit. The magnetic field produced will transfer the signal or power from the
transmitter to the receiver. The receiver and transmitter part is separated and the
maximum distance will be measured. The maximum distance achieved is 73.5cm
upward. This project can be improved by increase the frequency or supply voltage.
The high frequency can transmit signal better while high voltage can increase
voltage receive at the receiver.
vi
ABSTRAK
Teknologi hari ini berkembang pesat dan menjadikan alatan elektronik
semakin mudah untuk digunakan. Kebanyakkan orang juga gemar menukar-nukar
peralatan elektronik mereka tanpa memikirkan soal harga. Peralatan tanpa wayar
menjadi rebutan kerana mudah digunakan dan sebagai tanda kemajuan teknologi. Ia
juga dapat menyelesaikan masalah wayar berselirat yang boleh menyababkan
kemalangan. Situasi ini telah melahirkan idea untuk menghasilkan pengcaj tanpa
wayar. Alat ini menggunakan prinsip dan teknik induksi bermagnet. Induksi hasil
sendiri akan dipasangkan pada litar penghantar dan penerima. Kawasan bermagnet
yang terhasil akan memindahkan kuasa atau isyarat dari litar penghantar kepada litar
penerima. Jarak maksima antara litar penghantar dan penerima yang terpisah akan
diukur. Jarak maksima yang terhasil adalah 73.5sm. projek ini boleh dimajukan
dengan menambah bilangan pusingan pada induksi dan meninggikan voltan.
Frekuensi tinggi boleh memindahkan isyarat dengan lebih baik manakala voltan
tinggi pula boleh mininggikan voltan di litar penerima.
vii
TABLE OF CONTENTS
CHAPTER
1
2
TITLE
PAGE
DECLARATION
ii
DEDICATION
iii
ACKNOWLEDGEMENT
iv
ABSTRACT
v
ABSTRAK
vi
TABLE OF CONTENTS
vii
LIST OF TABLES
ix
LIST OF FIGURES
x
LIST OF ABBREVIATIONS
xi
LIST OF EQUATION
xii
INTRODUCTION
1.0 History And Background
1
1.1 Problem Statement
4
1.2 Objective
4
1.3 Scope Of Study
5
1.4 Introduction To Thesis
5
LITERATURE REVIEW
2.1 Previous Work
6
2.2 Charger
8
2.3 Induction
11
2.3.1 Type Of Inductor
12
2.3.2 Type Of Cores
13
viii
2.3 Inductive Power Transfer
14
2.4 Wireless Power Transfer
15
2.5 Rectifier
16
2.5.1 Shottky Diode
2.6 Voltage Regulator
2.6.1 Negative Feedback
3
4
5
REFERENCE
17
18
19
METHODOLOGY
3.1 Components And Instruments
21
3.2 Transmitter
22
3.3 Receiver
22
3.4 Implementation Of Circuit
26
RESULTS AND DISCUSSION
4.1 Results
28
4.2 Comparison At Varies Input
29
4.3 Comparison At Varies Frequency
31
4.4 Maximum Distance
33
4.5 Problems
35
CONCLUSION
5.1 Conclusion
36
5.2 Recommendation
37
38
ix
LIST OF TABLE
TABLE NO.
TITLE
PAGE
1.1
Comparison of existing charging process
3
4.1
Maximum distance
34
x
LIST OF FIGURES
FIGURE NO.
TITLE
PAGE
2.1
Example of simple charger
9
2.2
Various type of inductor
11
2.3
Inductive power transfer via air
14
2.4
Example of wireless power transfer system
16
2.5
Simple full wave rectifier circuit
17
2.6
Negative feedback voltage regulator circuit
19
1.
3.1
Function generator and digital oscilloscope
23
1.
3.2
Circuit for transistor
24
2.
3.3
Transmitter circuit
24
3.
3.4
Circuit of the receiver without voltage regulator
25
4.
3.5
Actual receiver circuit
25
5.
3.6
Flow chart of the circuit
26
6.
3.7
Block diagram of project
27
1.
4.1
Complete circuit
29
2.
4.2
Variation of input voltage
31
3.
4.3
Variation of frequency
33
4.
4.4
Illustrate of magnetic field
35
xi
LIST OF ABBREVIATIONS
AC
Alternate Current
AWG
American Wire Gauge
DC
Direct Current
ISM
Industrial, Scientific, and Medical
IPT
Inductive Power Transfer
PCB
Printed Circuit Board
xii
List of Equation
EQUATION NO.
TITLE
PAGE
2.1
Relationship voltage and inductance
11
2.2
Output voltage of negative feedback
20
regulator
2.3
Current of negative feedback regulator
20
4.1
Relationship voltage, frequency and speed
33
CHAPTER 1
INTRODUCTION
In today‟s world, portable electronic devices are very popular. As the
application of these portable electronic devices increasing, the demands for longer
battery life are also increasing. Thus, batteries need to be recharged or replaced
periodically. The conventional way of charging process is by using wire but
nowadays wireless charging start to take place in technology market. But the
charging process is still not totally wireless except for the fact that no wire is being
used. This is because the devices still need to be in contact with the charger. As
result, the wireless charger came out as the topic for this project. The advantage of
this device is, it can be totally wirelessly charge up a battery without the need to be
in contact with the charger.
1.0
History and Background
Wireless charging process exists long ago and was proposed by Nicola Tesla.
He proposed theories of wireless power transmission in the late 1800s and early
1900s. Tesla demonstrated the illumination of vacuum bulbs without using
2
wires for power transmission at the World Columbian Exposition in Chicago. Tesla's
work was impressive, but it didn't immediately lead to widespread, practical methods
for wireless power transmission.
In 1904, an airship motor of 0.1 horsepower was driven by transmitting
power over space from a distance of least 100 feet. Then in 1961, Brown published
the first paper proposing microwave energy for power transmission, and in 1964 he
demonstrated a microwave-powered model helicopter that received all the power
needed for flight from a microwave beam at 2.45 GHz from the range of 2.4GHz –
2.5 GHz frequency band which is reserved for Industrial, Scientific, and Medical
(ISM) applications. California on 1975 and at Grand Bassin on Reunion Island in
1997 is a place where experiments in power transmission without wires in the range
of tens of kilowatts were done.
Some types of wireless chargers are using Capacitive coupling,
Electromagnetic induction, Magnetic resonance, Radiowaves and solar energy ; but
all these existing charger has their own advantages and disadvantages. The goal of
this project was to create a wireless power transfer system that is capable of
transmitting power safely and efficiently. Table 1.1 shows a summary for six
different types of wireless charger.
3
Table 1.1 : Comparison of existing charging process
By comparing all the aspects, magnetic coupling induction was chosen as the
way of charging. It is because magnetic coupling induction is safe to use, has low
risk of electric shock, and can transmit high power at a distance. The process of
charging is by transmitting the alternating current (AC) in transmitter coil that
generates magnetic field, which will induce the voltage at receiver coil.
Existing inductive coupling charger is used in Oral-B rechargeable
toothbrushes by the Braun (Company) since early 1990‟s. Various type of research
was done to improve the charging process. One of the remarkable successes was the
Powermat. Current powermat was built in with powerbank. The main part will acts
as the transmitter and can charge only the mobile phone which has the receiver. The
charging process required contact between the powermat and mobile phone. Hence
came up with the idea of a circuit that could charge electrical device at certain
distance. For this project, plugged transmitter to the power supply instead of using
powermat concept was used. This circuit can be integrated with power bank in the
future.
4
1.1
Problem Statement
Today‟s common way to charge an electronic device is by using wire. If
there are many devices to charge at one time, the wire will be tangled and
dangerous. Some case of electrical related accidents is due to tangled wire. If
someone trip over the wire and the connection to power supply is not properly
connected, it will cause short circuit or the worst case is burning. So by using
wireless charger, this problem can be solved but not very convenient because the
devices and charger need to be in contact. So by using this product, the devices
can be charged away from the charger at certain distance comfortably.
1.2
Objective
The objective of this project is to determine whether a battery can be charge
wirelessly and find its distance. This project will use magnetic induction to transmit
the power wirelessly. Safety of this product is the main priority of this project. A
success in this project will prove that distance wireless charging can be improved
from time to time. This charger can charge low power devices only by using power
outlet.
5
1.3
Scope of Work
This project will use the magnetic induction process only. The output will be
identified by using oscilloscope to demonstrate the wave and determine the output
voltage. Function generator will act as AC voltage supply. The voltage supply in the
range of 0V -15V and the frequency between 100Hz – 100kHz. The variation of
frequency and supply voltage will be tested to identify its relationship.
1.4
Introduction to the thesis
Chapter 1 will cover the introduction and the background of wireless power
transfer and wireless charging. In addition, it also covers the problem statement that
results as the objective of this project. The scope of work also will be specified in
this chapter. Chapter 2 discusses about literature review and theory that will be used
in this project. The theory will be discussed one by one in each sub topics. While
Chapter 3 will discuss about the operation of this project and how the results will be
taken. Chapter 4 covers the results and discussion of this project. Some figure and
waveform will be included in this chapter. Chapter 5 contains the conclusion and
suggestion for future improvement.
CHAPTER 2
LITERATURE REVIEW
This chapter will cover about charger, inductor, inductive power transfer,
wireless power transfer, rectifier and voltage regulator. The entire topic discussed is
used and implemented in this project. The understanding in these entire topics gives
the successful result on this project. The ways of application of these topics will be
discussed in Chapter 3.
2.1
Previous work
The research and study according to development of wireless power transfer
had been done continuously to improve the results. In this few years, research
regarding wireless charger also start to take place.
In 2012, Tahsin, Naim
Muhammad, Siddiqui, Zaman, Mirza Imrul [16] proposed wireless charger for low
power devices using inductive coupling. In their research, they used antenna as the
transmitter to transmit the signal.
They have successfully accomplished their
objective to transmit the power using resonant coils from AC supply to resistive
load.
7
The transmitter was built using a 6 mm copper tube, 8.5 cm in length to
transmit the resonant frequency, while the receiver used 18 AWG copper wire with
8cm diameter. They faced problems during choosing the right components to use as
antenna, oscillator and capacitor. By solving the problems, they successfully get 6
inches of maximum distance or roughly 15cm before the signal was lost.[16]
Wireless transmission of power using PCB transformer with mobile
secondary was proposed by Hemche and Jaafari[11] . They study about the effect of
geometrical shape and electrical signal to the power transmission through the air.
An air transformer was used as the main component in their research. The primary,
secondary circuit and windings were printed on PCB. Mutual inductance was used
in this project to carry out their objective. They clarified that vertical displacement
between the primary and secondary circuit is at 7 cm when the mutual inductance is
at optimum but changed to negative signal when a distance between 8 cm to 9 cm
was reached. When the distance between the two winding was small, the power at
secondary coils decreased but the impedance become larger. The power received at
the secondary coil was 75 W and the magnetic coupling decreased slowly after the
distance reached 7 cm.[11]
Olvitz, Vinko and Svedek [9] did a research about wireless power transfer for
mobile phone charging devices. They used inductive coupling as medium to transfer
the electrical power or electrical signal. The circuit was also printed on PCB since it
will be implemented in a mobile phone.
The oscillator, power amplifier and
transmitter coils were generally on primary circuit. They also designed the charger
to control the current and transmitting power. The low pass filter was used to limit
the current from the oscillator. Parallel resonance was used to minimize the current
drawn at resonant achieved. Power transfer of 5 W at 2.5 cm distance between
primary and secondary was the results of their study. The objective of their study
was to charge mobile phone without disturbing the function of the phone was well
accomplished. [9]
8
Siamak Bastami, Technical Marketing Director at Integrated Device
Technology (IDT).inc [15] did a research on magnetic induction or magnetic
resonance for wireless charging process. He decided that magnetic resonance was
better compared to magnetic induction. It is because the designed resonant circuit
can provide freedom to charge mobile phone or other low power battery via direct
charging process. Direct charging means the charger and devices need to be in
contact for the charging process take place. Using magnetic induction would involve
the use of metal that would produced electromagnetic field and caused temperature
increased. This will bring damage to the devices. In order to develop new product
or innovation, all aspect need to be carefully revised to safeguard the safety of the
consumer.[15]
2.2
Charger
A battery charger is a device used to put energy into a rechargeable battery
by forcing an electric current through it. The charging process depends on the size
and type of the battery being charged. There are high tolerance and low tolerance for
overcharging. Battery that has high tolerance for overcharging and can be recharged
by connecting it to a constant voltage source or a constant current source. Simple
chargers of this type need manual disconnection at the end of the charge cycle, or
may have a timer to cut off charging process at a fixed time.
Battery types that cannot withstand long high rate of overcharging may have
temperature or voltage sensing circuits and a microprocessor controller to adjust the
charging current, and cut off at the end of the charging process. Slow battery
chargers may take several hours to complete the charging process while high rate
chargers may restore most capacity within minutes or less than an hour.
9
Overcharging need to be avoided for all type of batteries because it can decrease the
battery‟s lifespan.
Figure 2.1: Example of simple charger
A charging process starts at the secondary coil after the voltage being step
down from main power supply. The voltage will go through a rectifier to convert
from AC voltage into DC voltage. The capacitor after the rectifier, function as a
filter to smooth the wave after the conversion. Finally, the voltage will flow to the
battery and recharge process occur.
Allen T. Water stated some aspects that need to be considered when building
a charger.[1] This is a list of eight requirements used as a guide throughout the
design process:
1. Functional
It must transmit power wirelessly.
2. Safe
The completed system should create no risk to the user, devices or
environment. Risks include electric shock, damage of charged device, or
damage to other electronic devices in the environment.
10
3. Low cost
The application should be low cost, so it can be affordable to the masses.
4. Monitoring capabilities
The customer needs some mechanism for displaying what devices detected,
and whether they are fully charged.
5. Robust
Over the course of at least 20-hour testing period, the charger should neither
be physically damaged, nor should the efficiency reduce.
6. Efficient
The system should operate with at least 50% power efficiency, to remain
competitive with wired charging systems.
7. Versatile
Considering that a consumer will have many handheld electronic devices, the
system should be compatible with at least three different target devices.
8. Charging multiple devices simultaneously
Similar to the need for versatility, the system should be capable of supplying
power to at least three targets simultaneously but not necessarily identical.
11
2.3
Induction
Figure 2.2: Various type of inductor
An inductor is a passive element designed to store energy in its magnetic
field. It also consists of a coil of conducting wire. While inductance is the property
whereby an inductor exhibits opposition to the change of current flowing through it
and measured in Henrys, H. Inductors generate an opposing voltage proportional to
the rate of change of current in a circuit. This property is also called self-inductance
to differentiate it from mutual inductance, describing the voltage induced in one
electrical circuit by the rate of change of the electric current in another circuit.[2]
V=L
……….. 2.1
Where, V represents the voltage in volts and i the current in amperes.
Mutual inductance occurs when the change in current in one inductor induces a
voltage in another nearby inductor. It is important as the theory by which
transformers work, but it can also cause unwanted coupling between conductors in a
circuit.
There are various types of inductor and its core which will affect the
characteristic of the inductor. Type and core type has great effect towards its usage
and function.
12
2.3.1
Types of Inductors
Below are type of inductor and its specific applications. Coupled, multilayer,
ceramic core, and molded inductors are all common types found in commercial and
industrial applications:

Coupled Inductors
Coupled inductors show magnetic flux that is dependent on other conductors to
which they are connected. Coupled inductors are often used for mutual inductance.
A transformer is an example of coupled inductor.

Multi-Layer Inductors
This type of inductor consists of a layered coil and wound multiple times around the
core. As a result of the multiple layers and the insulation between them, multi-layer
inductors have a high inductance level.

Ceramic Core Inductors
Although there are many types of cores, a ceramic core inductor is unique in having
a dielectric ceramic core, meaning it cannot store a lot of energy but has very low
distortion and hysteresis.

Molded Inductors
These inductors are formed using plastic or ceramic insulation. Frequently used in
circuit boards, they can assume either a cylindrical or bar formation with windings
featuring terminations at each end.
13
2.3.2
Types of Cores
Aside from ceramic core inductors, other core materials can be used to
achieve certain results. Because the core is the material the coil winds around, it will
directly affect the inductance. Coils wound around iron-based cores produce greater
inductance than those wound around non-iron-based cores.

Air Core
In this configuration, there simply is no core. The lack of a metal core results in very
little distortion, but by the same token, the coil must be very long to carry high
amounts of inductance, resulting in a large inductor.

Steel Cores
For low resistance and high inductance applications, steel cores are a step above air
core. The denser the steel core, the less problem the core will encounter with
magnetic saturation.

Solid Ferrite Cores
When it comes to present the highest resistance, solid ferrite cores are at the top of
the list. However, when dealing with high inductance they are not always reliable
and tend to reach their magnetic saturation level quite quickly. Ferrite cores will use
a different ferrite material based on the application, such as manganese zinc for
certain kinds of antenna rods, with various materials offering a different set of
advantages. Powdered ferrite cores are available, which are denser and offer greater
linearity than solid ferrite cores.
14
2.4
Inductive power transfer
Inductive Power Transfer (IPT) refers to the concept of transferring electrical
power between two isolated circuits across an air gap. While based on the work and
concepts developed by pioneers such as Faraday and Ampere, it is only recently that
IPT has been developed into working systems.[7]
Basically, an IPT system can be divided into two parts; primary and
secondary. The primary side of the system is made up of a resonant power supply
and a coil. This power supply produces a high frequency sinusoidal current in the
coil. The secondary side (pick up) has a smaller coil, and a converter to produce a
DC voltage. This is proved in figure below:
Figure 2.3: Inductive power transfer via air
Wireless Charger for Low Power Devices using Inductive Coupling stated
that inductive power transfer has a number of advantages over other power transfer
methods. It is unaffected by dirt, dust, water, or chemicals. In situations such as coal
mining IPT prevents sparks and other hazards. As the coupling is magnetic, there is
no risk of electrocution even when used in high power systems. This makes IPT very
suitable for transport systems where vehicles follow a fixed track, such as in factory
materials handling.[16]
15
2.5
Wireless power transfer
Wireless power or wireless energy transfer is the transmission of electrical
energy from a power source to an electrical load without conductors or wires.
Wireless transmission is useful in cases where connecting wires are inconvenient,
hazardous, or impossible. The problem of wireless power transfer differs from that
of wireless telecommunications, such as radio. The proportion of energy received
becomes serious only if it is too low for the signal to be distinguished from the
background noise.
The most common form of wireless power transmission is carried out using
direct induction followed by resonant magnetic induction. According to G. A. Landis
in Applications for Space Power by Laser Transmission, 1996 , other methods under
consideration are electromagnetic radiation in the form of microwaves or lasers and
electrical conduction through natural media. [6]
Referring to Wireless Power Transfer for Mobile Phone Charging wireless
power transfer with inductive coupling is using an air core transformer where the
primary and the secondary are not fixed together like in a typical transformer. It also
can transfer power effectively at high frequency. But it can only operate with AC
voltage supply.[9]
Figure 2.4: Example of wireless power transfer system
16
The air gap is the gap between the ending parts of each core. The effect of the
air gap to the output voltage for different input voltages is investigated by Nasrul
Humaimi Mahmood, Mohamed Amin Alias, Mohd Wazir Mustapha, Mazlina Esa
and Faridah Taha (2003). It was found that, as the length of the air-gap is increased,
the output voltage is decreased by measuring input and output voltages in Volts, V
(AC Source) at the secondary core using different primary input voltage. This means
it is quite difficult to control the magnetic flux distribution when the air gap is
increased.[12]
Since two inductively coupled coils are used to transmit data wirelessly,
efficiency is increases when the coils are coupled at the same resonant frequency.
This resonant coupling method is the basic concept of the advanced technology
called Witricity. However, the high efficiency can only be maintained when the
impedance at both transmitting and receiving ends are same. But, the impedance
changes with the distance will cause the efficiency to decrease. This matter is stated
by Seung Keun Yoon, Sang Joon Kim, and Ui Kun Kwon in „Random Energy
Charging for Reviving Sensors in Wireless Sensor Network‟ on 2012. [14]
2.6 Rectifier
Figure 2.5: Simple full wave rectifier circuit
17
From Oxford English Dictionary 8th edition, rectifier means an electrical
device which converts an alternating current into a direct one by allowing a current
to flow through it in one direction only. There are two type of rectification; half
wave rectifier and full wave rectifier.[13]
Half wave rectification needs a single diode in a single phase supply or three
in a three phase supply. Rectifiers produce a unidirectional but pulsating direct
current; half wave rectifiers produce far more ripple than full wave rectifiers, and
much more filtering is needed to eliminate harmonics of the AC frequency from the
output. It will result either the positive or negative half of the AC wave is passed,
while the other half is blocked.[10]
A full wave rectifier converts the whole of the input waveform to one of
constant polarity at its output. Two diodes and a center tapped transformer, or four
diodes in a bridge configuration and any AC source including a transformer without
center tap, are needed. Single semiconductor diodes, double diodes with common
cathode or common anode, and four-diode bridges, are manufactured as single
components. [3]
2.6.1
Schottky Rectifiers
A Schottky rectifier is formed by making an electrically nonlinear contact
between a metal and the semiconductor drift region. The Schottky rectifier is an
attractive unipolar device for power electronics applications due to its relatively low
on state voltage drop and its fast switching behavior. It has been widely used in
power supply circuits with low operating voltages due to the availability of excellent
devices based upon silicon technology. In the case of silicon, the maximum
breakdown voltage of Schottky rectifiers has been limited by the increase in the
resistance of the drift region. Market available devices are generally rated at
breakdown voltages of less than 100 Volts.
18
Many applications require fast switching rectifiers with low on state voltage
drop that can also support over 500 volts. The much lower resistance of the drift
region for silicon carbide enables development of such Schottky rectifiers with very
high breakdown voltages. These devices not only offer fast switching speed but also
eliminate the large reverse recovery current observed in high voltage silicon P-i-N
rectifiers. This reduces switching losses not only in the rectifier but also in the
IGBTs used within the power circuits.
2.7
Voltage Regulator
A zener diode is low current device used for voltage regulation. For voltage
regulators capable of handling large currents, combination of zener diode with
negative-feedback amplifiers is necessary. The limitation on a zener diode regulator
is the changes in load current produce equal and opposite changes in zener current.
The changes in zener current flowing through the zener impedance produce changes
in the final output voltage. The larger the changes in zener current, the larger the
output voltage. If the changes in zener current are only a few milliamperes, the
changes in load voltage may be acceptable. But when the changes are tens of
milliamperes or more, the changes in load voltage become too large for most
applications.[2]
The simplest way to increase the current handling ability of a zener diode
regulator is to add an emitter follower. The load voltage still equals the zener voltage
(less the VBE drop of the transistor) but the changes in zener current are reduced by a
factor of β. Because of this, the regulator can handle larger load currents and still
maintain an almost constant load voltage.
19
2.7.1
Negative feedback
Figure 2.6: Negative feedback voltage regulator circuit
Figure 2.6.1 is an example of a negative feedback regulator. Transistor Q2
acts like emitter follower. Transistor Q1 provides voltage gain in a negative feedback
loop. When the load voltage increase the feedback voltage VF will increase. Since
the emitter voltage of Q1 is held constant by the zener diode, more collector current
flows through Q1 and through R3. This reduces the base voltage of Q2. In response,
the emitter voltage of Q2 decreases, offsetting almost all the original increase in load
voltage.
Similarly, if the load voltage tries to decrease, the feedback voltage VF
decreases. This reduces the current through Q1 and R3. The higher voltage at the base
of Q2 increases the emitter voltage of Q2 and this almost completely offsets the
original decrease in the load voltage.
Therefore, any attempted change in load voltage is compensated by negative
feedback. The overall effect is to produce an almost rock solid load voltage, despite
changes in load resistance.
20
A mathematical analysis leads to this expression for the output voltage:
Vout = ACL (VZ + VBE)
..…..……. 2.2
Where VZ is the zener voltage and VBE is the base-emitter drop of Q1. Also, the
closed-loop gain is
ACL = (R2/R1) + 1
..………… 2.3
By adjusting the ratio of R2 to R1, a regulated output voltage with essentially
the same stability as the zener voltage will be produced. RA in Figure 2.6.1 allows us
to adjust the output voltage to the exact value required in a particular application.
Thus, tolerance in zener voltage, VBE drops, and feedback resistors can be adjusted.
Summary
All the topics discuss above is used in the implementation of this project. The
topics on charger give the basic understanding on the charging process and
characteristics that need to be understood in build this project. Type of charger and
its core has been discussed in inductor‟s topic. This topic is important because this
project required self-build inductor. Inductive power transfer and wireless power
transfer will be applied together because it is the core of this project. Rectifier and
voltage regulator is discussed because it is important in constructing the charger.
CHAPTER 3
METHODOLOGY
This project is based on magnetic induction concept which will transfer the
power wirelessly through the air. In this chapter, the transmitter, receiver and how
the process work will be explained. The list of instruments and apparatus used will
also be defined. This project is done in a laboratory and some instrument was used
to determine the result of this project.
3.1
Components and Instruments
Below are the list of component and instruments used for this project.
•
24 AWG copper magnet wire
•
AC supply
•
2 10k resistor
•
1 1k resistor
•
8 150nF capacitor
•
Voltage regulator
•
4 Schottky diodes
22
•
Function generator
•
Digital oscilloscope
Figure 3.1 : Function generator and digital oscilloscope
3.2
Transmitter
The transmitter circuit of this project is made up of a power supply, resistors,
transistor and primary coil. All these components were built on donut board instead
of bread board because bread board cannot withstand higher voltage from power
supply. This transmitter does not need step down transformer because the supply
voltage for this circuit is taken from a function generator. The maximum voltage
supply is 10V. Function generator was used as power supply because instead of AC
power supply, it also has adjustable frequency. So the effect of variation of voltage
and frequency can be determined.
23
XFG1
R1
10kΩ
Q1
L1
C2
0H
150nF
2N2222A
C1
150nF
R2
10kΩ
R3
1kΩ
C3
150nF
Figure 3.2 : Circuit for transmitter
Figure 3.3 : Transmitter circuit
The primary coil is 2.5m long using 24 AWG magnetic coated wire. The coil
is connected between the input supply and emitter of the transistor. There are 18
turns of transmitter coils into the rectangle shape. The transistor can act as switch
and also as amplifier of electrical signal.
24
3.3
Receiver
The receiver circuit is where the charging process occurs and also known as
charger. The receiver circuit consists of receiver coils, capacitor, shottky diode,
capacitor and the output is connected to oscilloscope. The shottky diode acts as full
wave rectifier in this charger. The shottky diode was used instead of common diode
because it has a lower voltage drop. The rectifier will convert the AC voltage
receive from receiver coils into DC voltage. The capacitors after the rectifier act as
filter to smooth the DC wave after the rectification process. Then the output will be
connected to digital oscilloscope to display the output waveform.
The voltage
regulator was connected after the filter and before the oscilloscope. The output pin of
the voltage regulator will be connected to oscilloscope while the input pin to the
filter.
C6
XSC2
L1
0H
C4
0.1µF
0.15µF
C5
150nF
D1
1N5821
D2
1N5821
D7
1N5821
D8
C9
0.15µF
Ext Trig
+
C10
0.15µF
_
B
A
+
1N5821
Figure 3.4 : Circuit of the receiver without voltage regulator
_
+
_
25
Figure 3.5 : Actual receiver circuit
The receiver coils were made into circle in shape and the turns is 28 and the
diameter is 5cm. Eventhough the turns and diameter is different, the length of the
wire is the same 2.5m. The receiver circuit is built on donut board because it is easy
to move the circuit. The smaller circuit of receiver coils is better because it will be
implemented into electronic device. So the size of the circuit needs to be taken into
account.
26
3.4
Implementation of circuit
Figure 3.6 and 3.7 is the flow chart and block diagram for the project. The process
for this project follows the flow chart properly and the result is recorded. The block
diagram is show roughly the connection
Figure 3.6 : Flow chart of the circuit
27
Function generator
Transmitter
Oscilloscope
Receiver
Figure 3.7: Block diagram of project
After the transmitter and receiver circuit was connected, the function
generator and oscilloscope will be turned on. The receiver coil will be put inside the
transmitter coils.
First, set the function generator at low amplitude and low
frequency. It is decided to set the frequency at 5kHz while the amplitude is around
1.5V. After the output was recorded, the amplitude will be increase slowly until
maximum. At least 3 readings were taken and recorded.
Then the amplitude was set at 5V and the frequency was varied to see the
effects. The frequency chosen are 10kHz, 25kHz and 50kHz. All the results were
recorded and the effect will be discussed in Chapter 4. Lastly, the transmitter and
receiver coil will be pulled further from each other to determine the longest distance
the power can be transferred. All results will be discussed in chapter 4.
CHAPTER 4
RESULTS AND DISCUSSION
The results will be shown in waveform for variation of voltage and frequency
of the supply. This chapter will discuss on the effect of variation and maximum
distance of power transfer. For each topic, only three results will be compared and
discussed. The problem face in this project also will be mentioned at the end of this
chapter.
4.1
Results
Figure 4.1: Complete circuit
29
Figure 4.1 shows the complete circuit using 24 AWG magnetic coated wire.
The magnetic wire concept is used because it can function as transformer, to transfer
the power and act as inductor. Both coils will produce the magnetic field and cause
the induce voltage to flow in receiver coils. The magnet wire is coated to avoid short
circuit. The air core is chosen because it can transmit high frequency compared to
others cores. Both circuits are on donut board because it can withstand the higher
voltage and easy to used.
4.2
Comparison at different input voltage
This experiment output was taken from the output of the receiver circuit or
charging circuit. The results shows that the higher the supply the higher the output
voltages. This is because with a constant current through an inductor the voltage
drop across the inductor increases with an increase in the frequency of the applied
current. But with a constant current through a capacitor the voltage drop across the
capacitor decreases with an increase in the frequency of the applied current.
Because of that, the designed circuit has capacitor after the input and after the
receiver coils. It is to minimize the voltage drop that can cause the low output
voltage.
30
f = 5.0 kHz
A) Vout = 6.0mV
B) Vout = 4.8mV
C) Vout = 3.6mv
Figure 4.2: Variation of input voltage (A) Output voltage at Vin = 10V
(B) Output voltage at Vin = 5V (C) Output voltage Vin = 1V
31
As shown in Figure 4.2, we can see that as the supply voltage or amplitude
increase, the output voltage also increases. This proves that the high voltage will
increase the power transfer wirelessly. Even the maximum amplitude is being set,
the output voltage still small.
This is because the energy disperses greatly during
the wireless charging process. The waveform do not as smooth as the theoretical
waveform due to noise during the power transfer.
4.3
Comparison at different frequencies.
This experiment output was taken from the coils of the receiver circuit or
charging circuit. This is because the low voltage at the end of the process and the
signal is easily lost. So for batter results, output at the receiver coils is taken.
Normal charger, only 5 kHz frequency is needed because they transmit energy via
wire and no noise involve. But in wireless, noise factor will greatly affect the
transmitted signal. The results shows that the higher the frequency the higher the
output voltages.
The higher frequency can transmit the signal better than low
frequency because of the noise. If low frequency, the signal will be affected by the
noise and will result in signal lost. So this experiment, will prove the theory.
32
Vin = 5v
(A) f = 10 kHz
(B) f = 25 kHz
(A) f = 50 kHz
Figure 4.3: Variation of frequency (A) Output waveform at f = 10kHz (B) Output
waveform at f = 25kHz (C) output waveform at f = 50kHz
33
As shown, the signal or voltage at the output is higher as the frequency
increase. Because the signal do not undergo the rectification process yet, so the
signal is in sine wave since the input is AC power supply. The fixed input is 5V and
test frequency is 10 kHz, 25 kHz and 50 kHz. The higher frequency will cause the
signal to be unstable. This problem maybe due to not enough turns or the coil is
unable to support the frequency. The following equation shows the relationship
between frequency and the voltage.
………….. 4.1
F = frequency
N = speed.
4.4
Maximum distance
The next test was done to find the maximum distance. The input is set to
10V, the maximum voltage and the frequency is set to 50 kHz. The distance
between the transmission coils and receiver coils is measured perpendicularly and
side to side distance. The coil is being pulled in straight line. The results are shown
in table 4.1:
Table 4.1 : Maximum distance
Direction
Upward
Side to Side
Distance
73.5 cm
37 cm
The upward distance is greater than rear distance is because of the
concentration of the magnetic field. When pulling the receiver coils upward, the
magnetic field inside the coils is greater than outside of receiving coils. But the
magnetic field is weaker. Compared to side by side distance or side to side distance,
the coil is pulled away and the magnetic field becomes weaker and is lost. So the
34
distance is shorter compared to upward distance. The output voltage will decrease
slowly when the coils is being pulled away.
The figure 4.4 illustrates the
concentration of magnetic field inside and at the side of the core.
Figure 4.4 : Illustrate of magnetic field
35
4.5
Problems
The main problems in this project are unsuitable components for the coils.
Examples of wire use are 24 AWG and 14 AWG magnet wire and common jumper
wire. Finally 24 AWG was chosen; AWG stands for American Wire Gauge. The 14
AWG magnet wire produce the output but the output voltage was very low even the
when maximum frequency and input voltage is set compared to common magnet
wire and jumper wire which do not produce any readable results. So, 24 AWG
coated wire was chosen and it gave the best result.
The ways to measure the results also is a problem at beginning stage. During
project proposal and planning, LED is set as indicator in this project. But when the
LED did not light up even when there was reading on the multimeter. Oscilloscope
is decided to replace the LED. The LED did not light up due to very low voltage
produced at the output.
CHAPTER 5
CONCLUSION AND SUGGESTION
5.1
Conclusion
The objective of this project is successfully achieved in the time given. From
this project, it can be concluded that the results shows that power is successfully
transfered wirelessly.
The distance achieved is improved compared to others
research study. The study title „Wireless Charger for Low Power Devices using
Inductive Coupling‟ by Tahsin, Naim Muhammad, Siddiqui, Md. Murtoza, Zaman,
Md. Anik, Kayes, Mirza Imrul, they achieved 2.5cm but using different concept. So,
the magnetic induction is a revolution to a wireless battery charger to achieve 37cm
to 73cm.
Type and size of wire to build the coil also will affect the magnetic field.
The frequency and input voltage or power supply are also important in order to
achieve optimum wireless power transfer.
The power transfer is increased by
increasing the frequency and input power supply. So some recommendation is made
for further improvement.
5.2 Recommendations
From the results and discussion, frequency and amplitude of the power
supply have big influence in this project. So by improving the type of coils or
increasing the number of turns using higher frequency can give better to transfer.
Increasing power supply also will result in higher output voltage. By all these
improvement, the distance for wireless power transfer also will be increased. The
future projects, maybe new method of power transfer will be invented as the
improvement from this project. The wireless charger also can be improvised by
make into multi charging process at one time.
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