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)

Signature :

Name of Supervisor : ABD JAAFAR BIN SHAFIE

Date : 18th JUNE 2014

HIGH BRIGHTNESS LIGHT EMITTING DIODE DIMMER USING

FLYBACK CONVERTER

MOHD HAFIZ BIN ADENAN

A report submitted in partial of the

requirements for the award of the degree of

Bachelor of Engineering (Electrical)

Faculty of Electrical Engineering

Universiti Teknologi Malaysia

JUNE 2014

ii

I hereby declare that this thesis entitled High Brightness Light Emitting Diode

Dimmer Using Flyback Converter is the result of my research except as cited in the

references. The thesis has not been accepted for any degree and is not concurrently

submitted in the candidature of any other degree.

Signature : ..

Name of Author : MOHD HAFIZ BIN ADENAN

Date : 18TH JUNE 2014

iii

Dedicated to my beloved parents,

Tuan Haji Adenan bin Rashid and Puan Hajah Rohana binti Ismail, &

My caring and supportive brothers and sisters, lecturers, teachers, and friends.

iv

ACKNOWLEDGEMENT

All praises to God the Almighty, who has given me the strength that I need in

completing this final year project. First and foremost, my sincerest appreciation to my

supervisor, Mr Abd Jaafar bin Shafie for his encouragement, guidance and kind words

which have helped me write up this thesis. My appreciation too, to the lecturers who

contributed a lot of ideas and much insight into the development of this project. I also

would like to express my gratitude to Power Electronics Lab technicians, Mr Yusuf

and Mr Shafie, and my seniors for their invaluable suggestions, guidance and

assistance especially during tough times. A very special thanks to my beloved parents

for their love, motivation and continuous prayer, without which, I may not have had

the strength that pushed me to the finishing line, at least for this semester. Last but

definitely not the least, kudos to my friends, lab colleagues, and people around me who

have, directly or indirectly contributed towards the completion of my project. May

God bestow all of you with His kindness and love.

v

ABSTRACT

High brightness LED dimmer using Flyback converter is an LED driver in

which the brightness of LED can be controlled. Flyback converter is a DC-DC

converter that can produce variable output voltage. The magnitude of Flyback

converter output voltage can be set by setting the turn ratio at transformer and varying

the switching duty cycle. The Flyback converter transformer is usually designed with

an air gap for storage of energy. When the converter switch is ON, energy is stored in

the air gap. During switch OFF period, the stored energy in the air gap is transferred

to the output. LEDs are arranged in three parallel paths at the output side, where two

LEDs are placed in series in each path. A resistor is placed in series with those LEDs

in purpose to limit the current flowing through LED. By placing a resistor in series

with the LEDs, voltage changes across those LEDs are reduced as the voltage drop

across the resistor increases. LEDs are arranged in three parallel paths instead of one,

to reduce the voltage required to power ON the LEDs. The other purpose of arranging

those LEDs in three parallel paths is to ensure the other LEDs are still working if one

of the LEDs blows out or broken.

vi

ABSTRAK

Pemalap LED kecerahan tinggi menggunakan penukar Flyback ialah sebuah

pemacu LED yang mana kecerahan LED boleh dikawal. Penukar Flyback merupakan

salah satu daripada penukar DC-DC yang mampu menghasilkan voltan keluaran boleh

ubah. Magnitud voltan boleh disetkan dengan cara menetapkan kadar lilitan pada

pengubah dan dengan melaraskan kitar tugas suis. Pengubah penukar Flyback

biasanya direka bentuk dengan sela udara untuk tujuan penyimpanan tenaga. Ketika

suis tutup, tenaga disimpan di sela udara. Manakala ketika suis dibuka, tenaga yang

pada mulanya disimpan di sela udara dipindahkan ke bahagian keluaran. LED-LED

disusun dalam tiga barisan selari di bahagian keluaran, dengan setiap barisan

diletakkan dua LED. Perintang pengehad arus diletakkan secara siri dengan LED-LED

itu di setiap barisan untuk mengehadkan jumlah arus yang melalui LED. Ini untuk

mengelakkan arus berlebihan pada LED. LED-LED tersebut disusun secara selari

dalam tiga barisan supaya LED yang lain mampu berfungsi jika terdapat salah satu

daripada LED-LED tersebut terbakar atau rosak.

vii

LIST OF CONTENTS

CHAPTER TITLE PAGE

TITLE PAGE i

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRACT v

ABSTRAK vi

LIST OF CONTENTS vii

LIST OF TABLES x

LIST OF FIGURES xi

LIST OF ABBREVIATIONS xiii

LIST OF APPENDICES xvi

1 INTRODUCTION 1

1.0 Overview 1

1.1 Problem Statement 2

1.2 Objectives 3

1.3 Scope of Work 3

1.4 Thesis Outline 4

viii

2 LITERATURE REVIEW 6

2.0 Introduction 6

2.1 High Brightness Light Emitting Diode (HB LED) 6

2.2 Flyback Converter 8

2.2.1 Theory 8

2.2.2 Switching Technique 11

2.2.3 Transformer Air Gap 13

2.3 Rectifier 15

3 METHODOLOGY 16

3.0 Introduction 16

3.1 Design and Parameters Calculation 17

3.1.1 Flyback Converter 17

3.1.2 Pulse Width Modulation(PWM) 23

3.1.3 Rectifier 26

3.2 Simulation 27

3.2.1 Procedures 27

3.2.2 Preliminary Results 28

3.3 Circuit Building 29

3.3.1 Pulse Width Modulation 29

3.3.2 Gate Driver 30

3.3.3 Transformer and Flyback Converter 31

3.3.4 Rectifier 33

3.4 Hardware Implementation 34

4 RESULTS AND DISCUSSION 36

4.0 Introduction 36

4.1 Pulse Width Modulation Output 38

4.2 Gate Driver Output 38

ix

4.3 Transformer 39

4.4 Output Voltage 41

4.5 LED Brightness 43

5 CONCLUSION 45

5.1 Conclusion 45

5.2 Recommendation 46

REFERENCE 48

APPENDICES 50

x

LIST OF TABLES

TABLE TITLE PAGE

1 Flyback converter parameters 18

2 Transformer Core Parameters 22

3 Output voltage 43

xi

LIST OF FIGURES

FIGURE TITLE PAGE

1.1 Light Emitting Diode 2

1.2 LED schematic symbol 2

2.1 Flyback Converter HB LED Light Dimmer General Block Diagram 6

2.2 LED I-V Curve 7

2.3 Flyback Converter circuit 8

2.4 Flyback converter equivalent circuit during switch closed 9

2.5 Flyback converter equivalent circuit during switch opened 9

2.6 N-channel MOSFET with diode symbol and characteristic 12

2.7 PWM signal generation 12

2.8 PWM, Gate driver, and MOSFET 13

2.9 Magnetization curve of iron 14

2.10 Bridge rectifier 15

2.11 Bridge Rectifier Output Voltage 15

3.1 Flow chart of work plan 16

3.2 HB LED arrangement 17

3.3 HB LED model LWH3000 characteristic from [11] 18

3.4 PWM signal 23

3.5 External circuit of SG3525 24

3.6 Graph of timing resistor RT vs charge time[13] 25

3.7 Curves of dead time resistor, RD vs discharge time[13] 25

3.8 ACDC converter 26

3.9 Simulation circuit 28

3.10 Output voltage when D=0.3 28

3.11 Output voltage when D=0.4 29

3.12 PWM circuit on protoboard 30

xii

3.13 HCPL3180 Circuit Configuration 31

3.14 Coiled transformer bobbin without core 32

3.15 Flyback Converter on Protoboard 33

3.16 Step down transformer for bridge rectifier 34

3.17 Complete PCB Layout with Components 35

3.18 Complete LED light Dimmer using Flyback converter PCB 35

4.1 Schematic circuit of HB LED dimmer using Flyback converter 37

4.2 Output waveform of PWM 38

4.3 Gate Driver output waveform 39

4.4 Primary Winding Inductance 40

4.5 Secondary Winding Inductance 40

4.6 Voltage across Primary side of transformer 41

4.7 Output voltage waveform 42

4.8 LED brightness 44

xiii

LIST OF ABBREVIATIONS

LED - Light Emitting Diode

HB LED - High Brightness Light Emitting Diode

SMPS - Switched Mode Power Supply

DC - Direct Current

AC - Alternating Current

MOSFET - Metal-oxide-semiconductor Field Effect Transistor

BJT - Bipolar Junction Transistor

PWM - Pulse Width Modulation

IC - Integrated Circuit

VF - Forward Voltage

iL - Change of Inductance Current

Vs - Source Voltage

D - Duty Cycle

T - Period

f - Frequency

Lm - Magnetizing Inductance

N1 - No. of Turns of Primary Winding

N2 - No. of Turns of Secondary Winding

Vds(max) - Maximum drain-to-source Voltage

xiv

Vsec - Secondary Voltage

Vin - Input Voltage

VD - Diode Voltage

R - Resistance

L1 - Primary Inductance

L2 - Secondary Inductance

Ton - MOSFET ON period

Pout - Output Power

Co - Output Capacitor

vo - Output Voltage Ripple

H - Magnetic Field Intensity

Vo - Output Voltage

Vm - Peak Voltage

IF - Forward Current

N - Minimum Number of Turns

L - Inductance

lc - Length of Core

lg - Length of Air Gap

o - Air Permeability

r - Core Relative Permeability

Ac - Core Surface Area

Ag - Air Gap Surface Area

CT - Timing Capacitor

RT - Timing Resistor

xv

RD - Dead Time Resistor

RF - Forward Resistor

LCR - Inductance Capacitance Resistance

CAD - Computer Aided Design

PCB - Printed Circuit Board

RCD - Resistor Capacitor Diode

I-V - Current vs Voltage

xvi

LIST OF APPENDICES

APPENDIX TITLE PAGE

A HIGH BRIGHTNESS LED DATASHEET 50

B SG3525 PWM SIGNAL GENERATOR DATASHEET 53

C HCPL3180 MOSFET GATE DRIVER DATASHEET 58

D IL1212S SUPPLY ISOLATION DATASHEET 62

E MOSFET IRF510 DATASHEET 63

F ETD34 TRANSFORMER CORE DATASHEET 65

G VOLTAGE REGULATOR 78XX DATASHEET 72

H PRINTED CIRCUIT BOARD DESIGN LAYOUT 78

I HB LED DIMMER USING FLYBACK CONVERTER 79

CHAPTER 1

INTRODUCTION

1.0 Overview

Usage of High Brightness (HB) LED as a replacement to conventional light for

lighting application is slowly taking place in the global market. A report from the star

newspaper on 25th April 2013 entitled Soraa to raise orders of LED modules stated

that the LED market in Asia, especially in Japan and China is set to rise by the rate of

73.8% and 30% respectively by the year 2015[1]

Light Emitting Diode (LED) is one of the many unique electronic components

that are useful in daily life. Its operation is the same as diodes. LEDs applications are

notable that it is not only used as indicator lights, but also used to replace conventional

lights for general lighting[2]. LED generally is used as indicator lights like train

signals, traffic lights, and billboards because of its special ability which is its visibility

even from far away. High Brightness (HB) LED is newer compared to normal LED

and its applications for building lighting, road lighting, and pedestrian is growing

rapidly in Malaysia. The difference of HB LED compared to LED is that HB LED has

the ability to light up a dark room or space. HB LED has several advantages over

conventional lights. LED is more efficient, energy saving, smaller in size, longer

lifetime, rugged, and known for its fast turn on and turn off capability which make it

suitable for intelligent lighting[2].

2

Figure 1.1: Light Emitting Diode

Figure 1.2: LED schematic symbol

By designing the right circuit, LED brightness can be controlled, thus make it

applicable to more applications.

1.1 Problem Statement

To turn on the LED, the supply needs to be DC voltage, but the voltage

supplied to our houses from the utility is 240V AC. Therefore, despite its many

advantages, LED requires a driver for it to be turned on and the brightness to be

controlled.

There are many active topologies that can be used as LED driver and Flyback

converter is one of them[2]. Flyback converter is a Switched Mode Power Supply

(SMPS) that can do both jobs; turn on the LED and brightness control. It is a DC to

3

DC converter and has some advantages over the other SMPS topology such as simple,

low in cost, not difficult to design[3] while providing isolation between input and

output side thus make it safer. Brightness of HB LED in Flyback converter is

controlled by adjusting the duty cycle of the switch.

Flyback converter is a DC to DC converter therefore it requires DC voltage to

operate, but the utility provides us AC voltage to our houses. To solve this, we need to

convert the AC supply to DC by using rectifier. Since the DC input that we need for

the Flyback converter is low, we will use a bridge rectifier with a step down

transformer and then the output voltage of the rectifier is regulated by using voltage

regulator. The regulated voltage source will then connected to the input of Flyback

converter.

1.2 Objectives

1. To study the working principle of a Flyback converter

2. To design a High Brightness Light Emitting Diode (HB LED) light dimmer

using Flyback converter topology

3. To build the hardware of the HB LED light dimmer

1.3 Scope of Work

The first thing we need to study before starting this project is the specification

of the HB LED that we are going to use in this project. The specification of the HB

LED is important because everything that we design in the circuit will be designed

with respect to our output which is the HB LED itself.

We also need to understand the working principle of Flyback converter as it is

the core of our project. We have to understand what occurs during its switch ON

4

condition and what occurs during switch OFF. Knowledge about the transformer of

Flyback converter need to be well studied and understood. We also need to study the

input source part, the switching part, the Flyback converter transformer, and many

more.

Once we understand the working principle of Flyback converter, then we can

start designing our Flyback converter HB LED light dimmer circuit. Calculations were

made in the design process. Designed circuit was simulated to confirm that all

calculations are correct. Results from simulation are considered as the preliminary

result. When all values were set and the design had been finalized, the hardware of HB

LED light dimmer using Flyback converter was built. The hardware was then

analyzed.

1.4 Thesis Outline

Chapter 1: Introduction

Chapter 1 is basically the part where High Brightness LED is introduced. Some

of its applications and problems regarding LED such as the requirements of the driver

are also described in this chapter. Other than that, the driver that we are designing,

Flyback converter is explained briefly.

Chapter 2: Literature Review

Global market trends of Flyback converter HB LED light dimmer is discussed

in this chapter. The working principle of LED and Flyback converter are reviewed.

Formulas, graphs, and other graphical methods are used to ease up the explanation

process.

5

Chapter 3: Methodology

The methodology, including calculation, simulation, and procedures that were

used when conducting this project are explained as detailed as possible in this part.

The steps used during the implementation of HB LED light dimmer are explained in

details. The results of theoretical calculation and simulation are presented here.

Chapter 4: Result and Discussion

The analysis results of hardware are described in here. That includes the final

circuit diagram, the output waveform, observations and others. The analysis result of

the hardware was compared to the theoretical and simulation results. Results of

hardware are discussed.

Chapter 5: Conclusion

The summary of the project and recommendations to improve the final circuit

are discussed here.

CHAPTER 2

LITERATURE REVIEW

2.0 Introduction

The theory and literature review of the components in the circuit of this project

are discussed in this chapter. Figure 2.1 shows block diagram of HB LED light dimmer

using Flyback converter.

Figure 2.1: Flyback Converter HB LED Light Dimmer General Block Diagram

2.1 High Brightness Light Emitting Diode (HB LED)

Light emitting diode (LED) is a type of diode that produces light when current

flows through it[4]. LED is a semiconductor based device and its operation principle

is the same to diode. It conducts current and emits light when the forward voltage

is reached and blocks current when reverse biased.

7

Figure 2.2: LED I-V Curve

High Brightness LED (HB LED) nowadays are applied in lighting applications

such as vehicle lights, home, street lighting and many more. It is predicted that the

high brightness LED is going to be the future trend in lighting application as it has

many advantages over conventional lights that we use today[2].

LED is better in efficacy. For the same luminous intensity, the power

consumption of an LED is lower compared to the power consumption of conventional

lights. LED can last longer. LED can last up to 50000 hours, dependent on the peak

current and temperature. LED is one of the products that promotes environmental

friendliness because it is produced without mercury. LED is semiconductor based,

therefore it is resistant to shock. Other than that, LED is known for its fast and easy

turn on and turn off, which make it suitable for intelligent lighting.

Nevertheless, HB LED cannot be supplied with the power supply techniques

that are used in powering up conventional lights. Therefore the development of

topologies specifically designed to power up HB LED is mandatory[2].

8

2.2 Flyback Converter

In this chapter, the theory of a Flyback converter, the switching technique, and

the reason behind the creation of the transformer air gap are explained.

2.2.1 Theory

Flyback converter is one of the many Switched Mode Power Supply (SMPS)

topologies that were developed in purpose to produce a DC output voltage that is

higher or lower than supplied DC input voltage. Flyback converter has several

advantages over the other SMPS topologies. The first advantage of Flyback converter

is it is simple and easy to design[3]. In terms of safety, Flyback converter is safe

because it provides isolation at the transformer which makes the output side separated

from the input side or the source. As shown in Figure 2.3 below, the dot sign at the

primary side and secondary side represents the relative polarity of the coupling

inductance. From the circuit figure below, we can see that the relative polarity of the

coupling inductance is opposite to each other[5-7].

Figure 2.3: Flyback Converter circuit

Flyback converter circuit analysis can be divided into two parts, the analysis

during switch ON and analysis during switch OFF. Figure 2.4 shows the condition

when the switch is ON. Current from the voltage source flows into the primary side,

9

but the current cannot flow at the secondary side at the same time as the primary

because the diode on the secondary side is reversed biased. Therefore the primary

winding is magnetized and magnetic energy is stored in the air gap.

Figure 2.4: Flyback converter equivalent circuit during switch closed

The equation of magnetizing inductance, Lm current during switch closed is[6]:

(()) =

(2.1)

When the switch is opened, the energy stored in the air gap is released and

current at the secondary winding flows through the forward biased diode along with

the energy stored.

Figure 2.5: Flyback converter equivalent circuit during switch opened

The equation that can be yielded from the equivalent circuit during switch opened

is[6]:

10

(()) = (1)

1

2 (2.2)

The sum of current that flows into and out of the transformer or the net change of the

current must be equal to zero[6]:

() + () = 0 (2.3)

(1 )

12

= 0

Rearranging the equation to get the output voltage:

= (

1)(

1

2) (2.4)

The other equations that were used are:

MOSFET drain-to-source maximum voltage[7]:

(max) = +1

2((max)) (2.5)

HB LED forward current:

=2

(2.6)

Where 2VF represents forward voltage of two LEDs.

11

Primary Inductance[7]:

1 =()

2

2.5 (2.7)

Relationship of turns ratio and inductance[8]:

1

2=

1

2 (2.8)

The output capacitor[7]:

=

(2.9)

2.2.2 Switching Technique

In power electronics, transistors act as switches. There are several types of

switches such as diodes, thyristors, and transistors. All of these switches are different

in terms of size of current and voltage that they can withstand, controllability,

switching speed, and its power losses.

As we can see in the Flyback converter schematic circuit in Figure 2.3,

MOSFET from transistor family is used as a switch. MOSFET is chosen over Bipolar

Junction Transistor (BJT) because it is better at switching speed and has lower

switching losses[6].

12

Figure 2.6: N-channel MOSFET with diode symbol and characteristic

MOSFET is turned ON by applying voltage to its gate and it stops conducting

current when the gate is no longer supplied with voltage. The gate is usually controlled

by Pulse-Width Modulation (PWM). PWM signal can be generated by using integrated

circuits (IC) such as LM2743, SG3525, SG3524, SG3526, and many more. Pulse

width can be controlled by adjusting the reference voltage.

Figure 2.7: PWM signal generation

As shown in Figure 2.7, the saw tooth voltage is compared to the reference

voltage. If the saw tooth voltage is lower than the reference voltage, the output signal

will be high and vice versa. ON period, over switching period, T, is called duty

cycle.

=

(2.10)

Duty cycle varies from 0 to 1. The higher the duty cycle, the longer the ON period.

13

Figure 2.8: PWM, Gate driver, and MOSFET

The PWM generator, SG3525 must be isolated from the MOSFET. In this

project, Optocoupler MOSFET gate driver is used for isolation of the PWM generator

from MOSFET.

2.2.3 Transformer Air Gap

A magnetic field is produced around a conductor when it carries current. The

thumb rule can be used to demonstrate the direction of the magnetic field when a

current is passed through a conductor. The magnetic field intensity depends on the

magnitude of current. When current increases in the transformer coil, magnetic field

intensity, H will also increase[9].

Unlike typical transformers, Flyback converter transformer or coupling

inductance will first store the energy during switch ON period and will release the

energy to the secondary the switch is OFF[3]. Flock of energy in the transformer can

cause core saturation at the transformer core if the transformer is not designed

properly. Transformer in Flyback converter is designed with an air gap to avoid flock

of energy.

14

Figure 2.9: Magnetization curve of iron

Observe the magnetization curve in Figure 2.9 above. Flux density goes into a

saturation level if the magnetic flux is too high. Saturation of flux density in the core

can cause overheating, hissing sound, and vibration[7]. This does not happen in typical

transformers because they do not have the function of energy storage, hence the flux

density is kept low[7].

The center leg of a Flyback converter transformer core is gapped to ensure that

flux density is kept low. Flux density increases slowly in the air compared to magnetic

materials. Therefore, chances of magnetic saturation to happen is lessened by gapping

the transformer core. By doing this, a large part of the energy will be stored in the air

gap[3, 7, 9]. At the end of every switching cycle, magnetic flux must return to its initial

value to avoid flux increment[7]. This means that the most suitable mode to design a

transformer for a Flyback converter is the discontinuous current mode. In this mode,

all of the stored energy will be transferred first to the secondary side before the start

of a new cycle[7]. Therefore, during the start of the new cycle, the magnetic flux in

the transformer core has returned to zero. Other than that, the inductance should not

be too low as it will cause current to rise faster.

15

2.3 Rectifier

A rectifier turns an alternating current (AC) voltage source to a direct current

(DC). Direct current is defined as a current which flows in one direction, such as the

current drawn from a battery[10].

Figure 2.10: Bridge rectifier

Figure 2.11: Bridge Rectifier Output Voltage

DC voltage is calculated by the equation[6]:

=1

0sin() = 2

(2.11)

CHAPTER 3

METHODOLOGY

3.0 Introduction

In this chapter, procedures in completing this project are discussed. This

includes the steps in designing and simulating the designed circuit. Calculations made

are shown. Results from calculations and simulation were analyzed and compared. The

flow chart below shows the work plan for this project.

Figure 3.1: Flow chart of work plan

17

3.1 Design and Parameters Calculation

The design and parameters calculation were made according to the theory

studied. This chapter comprises of design of Flyback converter, design of pulse width

modulation generation circuit, and rectifier circuit.

3.1.1 Flyback Converter

Before the calculations were started, properties of the output for this project,

which is the High Brightness Light Emitting Diode (HB LED) was studied. This is

important because everything was designed respected to the output. The HB LED used

is from model LWH3000 and the number of HB LEDs used is six. These HB LEDs

were put in three parallel paths. In each path, two HB LEDs and one current limiting

resistor were arranged and put in series. The configuration is shown in Figure 3.2. A

current limiting resistor is put to ensure that the current in each path is equal. The

current limiting resistor can also help avoid overcurrent at those LEDs.

Figure 3.2: HB LED arrangement

18

Figure 3.3: HB LED model LWH3000 characteristic from [11]

Other than the specifications of HB LED, to initiate the design process, other

parameters such switching frequency, input voltage, secondary side voltage and

current, the duty cycle of PWM that can produce such secondary voltage, coupling

inductance winding ratio, and output voltage ripple were identified. We also ought to

identify the mode whether it is continuous or discontinuous. In this project,

discontinuous mode was selected. The formula for an ideal Flyback converters

secondary or output voltage is from equation (2.4)[5, 6]:

= (

1 )(

12

)

Other parameters are as in Table 1:

Table 1: Flyback converter parameters

Switching frequency 50 kHz

Input voltage 18V

D Duty cycle 0.3 to 0.4

Secondary side voltage 7.7V to 12V

Secondary side current 15mA to 67.5mA

Output power 11.5mW to 81mW

1: 2 Transformer ratio 1:1

Secondary side voltage ripple 0.05V

19

3.1.1.1 MOSFET Rating

Calculation of maximum drain-to-source voltage stress, (max) on the

transistor was done to determine the rating of the MOSFET. This was done to ensure

that the MOSFET that we select can withstand the voltage stress during the OFF

period. Neglecting voltage spike caused by leakage inductance, the formula is, from

equation (2.5)[7]:

(max) = +12

((max))

(max) = 18 +1

1(12) = 30

Therefore, the rating of the drain-to-source voltage must be at least 30V.

3.1.1.2 Current Limiting Resistor

Current limiting resistor value was calculated to ensure that the current

produced is suitable for the HB LED. Voltage drop at diode, at the secondary side

were considered. Forward current of HB LED, from equation (2.6) is:

= 2

Trial and error were done by varying the resistor value to get the right

combination of for the duty cycle of 0.3 and 0.4. Forward current of HB LED,

must be within the operating region of HB LED. The operating region can be seen

from the characteristic graph in Figure 3.3. Diode voltage drop, , 1.1V was taken

from the datasheet of model 1N4002 diode[11]. After trial and error, the current

20

limiting resistor that is suitable for the circuit is 200. Proves of calculations are as

follows:

For duty cycle of 0.4 which produces of 12V:

=12 1.1 2(3.2)

200= 22.5

For duty cycle of 0.3 which produces of 7.7V:

=7.7 1.1 2(2.8)

200= 5

The calculated currents are the current that flow in each parallel path. As

mentioned before, LEDs are arranged in three parallel paths. Therefore, the maximum

total current in the secondary side is 3*. The maximum total current in the secondary

side would be 67.5mA.

3.1.1.3 Transformer

The transformer must be designed properly to make sure the circuit operates as

desired. Calculations in designing a transformer are divided into three parts, which are

air gap length calculation, winding turns calculation, and winding copper diameter

calculation.

Before calculations stated above were done, the inductance of the transformer

was calculated first. The inductance of the transformer will determine the current

ripple at the output of the circuit. The bigger the inductance, the lower the current

21

ripple. To calculate the minimum inductance, the formula used is from equation

(2.7)[7]:

1 =()

2

2.5

1 =(18 8)2

2.5 20 81

1 5

To calculate minimum secondary inductance, we use equation (2.8)[8]:

12

= 12

2 = (21

)2

1

21

= 1, therefore:

2 = 1 = 5

The transformer was designed to achieve inductance calculated above. The equation

to calculate air gap length and number of turns is:

2 = (

0+

0

)

22

Where:

Table 2: Transformer Core Parameters

N Minimum number of turns

L Inductance

lc Length of core

lg Length of air gap

o Air permeability

r Core relative permeability

Ac Core surface area

Ag Air gap surface area

Length of core, core relative permeability, core surface area, and air gap

surface area were obtained from datasheet of ETD34 3C90 transformer core[12].

Length of air gap of 0.5mm was selected for this project. After calculations, the

minimum number of turns is 50 turns for both sides of the winding. Winding copper

wire was wounded three times the calculated value to avoid magnetic saturation from

happening. So, the winding copper wire is wounded 150 times.

Winding copper wire size was selected by calculation. The diameter of the wire

must be big enough to carry the current that flows through it. After calculation, the

minimum diameter of winding copper wire needed is 0.24mm. Winding copper wire

of diameter 0.5mm was selected.

3.1.1.4 Output Capacitor

Output capacitor was put to filter voltage ripple on the secondary side. Hence

it must be designed with respect to the voltage ripple itself. The formula to calculate

the output capacitor is equation (2.9)[7]:

23

=

For voltage ripple of 0.05V:

=12 0.4

0.05 50

2000

3.1.2 Pulse Width Modulation(PWM)

In PWM, there are three main parameters that were considered when designing

the IC configuration which are frequency, signal amplitude, and duty cycle. SG3525

IC is turned on by supplying 12V to leg number 15 from the 12V voltage regulator,

7812 IC. Leg number 12 is connected to the ground[13].

Figure 3.4: PWM signal

The full configuration of IC SG3525 is shown in Figure 3.5.

24

Figure 3.5: External circuit of SG3525

3.1.2.1 Frequency

The external circuit at legs number 5, 6, and 7 determines the frequency of the

PWM. Figure 3.7 of semi log graph of timing resistor, vs charge time and dead

time resistor, vs discharge time below were taken from the datasheet of SG3525

IC[13]. To obtain a frequency of 50 kHz, the total time taken for charging time added

by the discharging time must be 20s. Therefore, the timing capacitance, selected

for this circuit is 10nF, whereas is 0 and is between 2k and 5k. For ,

potentiometer of 5k is used so that the period of exactly 20s can be obtained. As

we can see in the Figure 3.6 below, must be connected to leg number 6 and ground.

Discharge resistor, must be put between leg number 5 and number 7 while is

connected to leg number 5 and ground.

25

Figure 3.6: Graph of tim [ng resistor RT vs charge time[13]

Figure 3.7: Curves of dead time resistor, RD vs discharge time[13]

3.1.2.2 Signal amplitude

Signal amplitude depends on the magnitude of voltage that is supplied to leg

number 13, the VC leg. In this project, leg number 13 is connected to leg number 16,

the output voltage of the IC SG3525s internal 5.1V voltage regulator. That means the

amplitude of the PWM output signal of the IC will be 5.1V. Output A signal leg

number 11 is then connected to MOSFET gate driver, Optocoupler HCPL 3180 with

the intervention of a forward resistor in between them.

3.1.2.3 Duty cycle

The duty cycle of PWM is controlled by the internal error amplifier of the IC.

Leg number 1 is the inverting input and leg number 2 is the non-inverting input. The

26

internal error amplifier compares the voltage at both legs. The duty cycle of PWM

signal will decrease if the voltage at the inverting input (leg 1) is higher than non-

inverting input (leg 2) and vice versa. In this project, leg number 1 is short circuited to

leg number 9. Whereas leg number 2 is connected to a voltage divider resistor. The

error amplifier acts as a voltage follower in this configuration. A potentiometer is used

as the voltage divider resistor.

3.1.3 Rectifier

Full Wave Bridge Rectifier is used in this project to convert the AC supply to

DC to power up the whole circuit. Power source from socket have a voltage of

230, and is too high for the circuit. 230 of supply yields peak voltage, of

325V. Lower peak voltage is needed to supply IC 7818 in Figure 3.8. Therefore, a

230V:23V transformer is placed between socket power supply and bridge rectifier.

The output peak voltage of the transformer would be 32.5V. The circuit configuration

is as shown in Figure 3.8 below. Co is placed parallel to the rectifier output to filter the

output voltage ripple.

Figure 3.8: ACDC converter

27

3.2 Simulation

Simulation was done using Pspice software. This software is simple and

convenient for electrical or electronic circuit simulation.

3.2.1 Procedures

Steps to use Pspice:

1. Open pspice schematic windows

2. Draw the circuit that is going to be simulated

3. Configure parameters

4. Click setup analysis and check transient on setup analysis windows

5. Click on transient and set final time

6. Save the schematic

7. Click simulate to simulate the circuit and OrCAD Pspice A/D Demo

windows will pop up

8. At the OrCAD A/D windows, click add trace and select the voltage or

current that we want to analyze

9. Analyze the result

Figure 3.9 shows the circuit that was simulated in this project. In simulation,

LEDs were represented by diodes. Diodes were used instead of resistors because

diodes have the same characteristic to LED. However, diodes forward voltage is lower

than that of HB LEDs. D1N4002 diode in Pspice has a forward voltage of 0.8V while

forward voltage one HB LED varies from 2.8V to 3.2V. For duty cycle of 0.3 where

the forward voltage of one HB LED should be 2.8V, seven diodes were placed in series

to represent two HB LEDs. Total forward voltage of two HB LEDs with a forward

voltage of 2.8V is 5.6V while total forward voltage of seven diodes with forward

voltage of 0.8V is also 5.6V.

28

For duty cycle of 0.4, the forward voltage of one HB LED is 3.2V. Total

forward voltage of two HB LEDs and eight diodes are equal which is 6.4V. Therefore,

two HB LEDs with a forward voltage of 3.2V were represented by eight diodes of

forward voltage 0.8V.

Figure 3.9: Simulation circuit

3.2.2 Preliminary Results

Figure 3.10 below shows the output voltage when duty cycle is set to 0.3. When

duty cycle is set to 0.3, the output voltage at steady state is 7.0V.

Figure 3.10: Output voltage when D=0.3

Figure 3.11 shows the output voltage when duty cycle is set to 0.4. When duty

cycle is set to 0.4, the output voltage at steady state is 10.9V.

Time

0s 5ms 10ms 15ms 20ms 25ms 30ms 35ms 40ms 45ms 50ms

V(C1:2)

0V

2.0V

4.0V

6.0V

8.0V

(45.083m,6.9992)

29

Figure 3.61: Output voltage when D=0.4

3.3 Circuit Building

The circuit was built on a protoboard before implementation of hardware.

Protoboard was used because modification of circuit is possible in case the circuit is

not working as desired.

3.3.1 Pulse Width Modulation

The first part built and tested was Pulse Width Modulation. SG3525 is used to

generate PWM signal. The configuration of PWM part of this project hardware is

shown in Figure 3.5. The circuit built on protoboard is shown in Figure 3.12.

Time

0s 5ms 10ms 15ms 20ms 25ms 30ms 35ms 40ms 45ms 50ms

V(C1:2)

0V

4.0V

8.0V

12.0V

30

Figure 3.72: PWM circuit on protoboard

The circuit was successful after several times of modification. The

modifications were made until the desired output is obtained from the circuit. Some of

the modifications made were:

1. Placing filter capacitor at leg number 15 and 16 of SG3525 to regulate the

voltage.

2. Replacing oscillator timing resistor, with a lower value than the used for

the first circuit to get a higher frequency.

3. Replacing voltage divider resistor for duty cycle control to get a better duty

cycle range.

3.3.2 Gate Driver

The MOSFET gate driver used in this project is Optocoupler IC HCPL3180. A

voltage supply which is isolated from SG3525 is required to power up this IC.

Therefore, IL1212S is used to create an isolated voltage supply from the existing

voltage supply. IL1212S is supplied with 12V from 12V Voltage Regulator IC 7812

and produces an isolated 12V voltage supply at its output. Output of IL1212S is then

connected to Optocoupler HCPL3180. The circuit configuration of this IC is as shown

in Figure 3.13.

31

Figure 3.83: HCPL3180 Circuit Configuration

The gate driver input leg is connected to the output leg of SG3525 with the

mediation of a resistor . Calculation of is as follows:

=

= 5.1 1

10= 410 400

is the forward voltage of internal diode of HCPL3180 and forward current

is current required at the diode. All of the information was obtained from

HCPL3180 datasheet[14].

3.3.3 Transformer and Flyback Converter

The process of building Flyback converter is discussed here. This includes the

process of building the transformer.

32

3.3.3.1 Transformer

Building a transformer requires theoretical knowledge of electromagnetism

and power electronics. This knowledge is important when making such decisions as

transformer core size, winding copper diameter, air gap length, and number of turns of

winding copper because all of the mentioned criteria affect the inductance value of the

transformer. Parts needed to build the transformer for this project are two ferrite cores,

a bobbin or also known as coil former, two clips, winding copper, and polyester tape

to separate copper winding layers. For this circuit, ETD34 3C90 ferrite cores are used.

Bobbin and clips were selected according to the ferrite core type.

The building process of transformer was started by coiling 0.5mm diameter

winding copper wire 150 times for primary winding. The coiling process was

continued for secondary side of the transformer. The direction of winding is the same

for primary and secondary sides of the transformer. Insulation paint at the end of the

winding copper wire was removed by using a knife. Those ends were connected to

transformer bobbin legs. The polarity of the transformer is determined by the

connection at those legs.

Figure 3.94: Coiled transformer bobbin without core

Then, the center leg of the transformer was filed using a file. The purpose of

the filing is to make an air gap in the core of the transformer. As stated earlier in chapter

33

3.1.1.3, the air gap length decided is 0.5mm long. Therefore, the center leg is filed up

until the gap reaches 0.5mm. The value of inductance in each side of the transformer

was measured using an LCR meter. The measurement was made to make sure the

values of inductance are close enough to calculated values.

3.3.3.2 Flyback Converter

Flyback converter is built on protoboard after the transformer is wounded and

measured. The circuit was then tested and analyzed.

Figure 3.105: Flyback Converter on Protoboard

3.3.4 Rectifier

Rectifier is the last part to be built and analyzed before the full circuit is

finalized. Rectifier circuit was built according to schematic circuit in Figure 3.8. The

already built Flyback converter was then connected to the output rectifier and tested.

The result was successful.

34

Figure 3.116: Step down transformer for bridge rectifier

3.4 Hardware Implementation

The finalized circuit was then implemented on a Printed Circuit Board (PCB).

PCB layout was sketched using Eagle CAD software. The procedure of using Eagle

CAD is:

1. Open Eagle CAD software

2. Click File > new > project

3. Rename the title to PSM

4. Click PSM > new Schematic > open schematic

5. Sketch the circuit

6. Click Add > find components (components selected sizes must be measured)

7. Draw a complete circuit

8. When the circuit is complete, click File > Switch to Board

9. Arrange the components according to the requirements and creativity

10. Save

Figure 3.17 shows the designed PCB layout with components. Those

components can be made invisible at view section on Board windows.

35

Figure 3.127: Complete PCB Layout with Components

The complete layout was printed on a photo paper and laminated on a blank

copper board until all of the carbon printed on the photo paper sticks to the copper

board. Only then, the copper board was etched by using acid. Components, ICs,

jumpers, and connectors were then soldered according to design.

Figure 3.138: Complete LED light Dimmer using Flyback converter PCB

CHAPTER 4

RESULTS AND DISCUSSION

4.0 Introduction

In this chapter, the performance evaluation of the hardware is presented. Full

schematic circuit of the High Brightness LED dimmer using Flyback converter is

shown. The value of the inductances of primary and secondary side of the transformer

was measured. The waveforms of pulse width modulation, gate driver, the voltage

across the transformer at primary and secondary side, and output voltage of the

hardware were observed and discussed.

4.1 Complete Circuit

The full circuit of High Brightness LED dimmer using Flyback converter is

shown in Figure 4.1.

37

Figure 4.1: Schematic circuit of HB LED dimmer using Flyback converter

38

4.2 Pulse Width Modulation Output

Pulse width modulation (PWM) output waveform is obtained at the output of

the PWM generator IC, SG3525. Oscilloscope probes were clipped at leg number 11

and leg number 12. Figure 4.2 shows the output waveform of PWM.

Figure 4.2: Output waveform of PWM

The amplitude of PWM is 5V because leg number 13 is connected to leg

number 16 which is the output of the internal voltage regulator that generates 5V. The

frequency of the PWM signal is 50 kHz. The frequency was set at legs number 5, 6,

and 7 where CT and RT are placed. The duty cycle can be varied from 0 to 0.47 by

varying variable resistor that connected to leg number 2.

4.3 Gate Driver Output

The waveform of gate driver was measured across legs number 6 and 7 of the

gate driver IC, Optocoupler HCPL 3180. Figure 4.3 shows the output waveform of the

gate driver.

39

Figure 4.3: Gate Driver output waveform

The amplitude of the PWM signal is amplified and smoothed out by the gate

driver. As shown in Figure 4.3 above, the amplitude of the PWM signal is amplified

to 11.4V. The value is suitable to turn ON the MOSFET in the Flyback converter. The

signal is smoother compared to the PWM signal generated while frequency and the

duty cycle is retained from the PWM signal.

4.4 Transformer

Upon completing the building process of transformer, the value of inductances

on both sides were measured using an LCR meter and compared to the calculated

value. The figures below show the measured values of inductances at the transformer.

40

Figure 4.4: Primary Winding Inductance

Figure 4.5: Secondary Winding Inductance

The value is acceptable, even though it did not reach the targeted value which

is 5mH. The value can be reached if the center leg of the transformer is filed exactly

to the length that we calculated earlier, 0.5mm.

The voltage across primary side was observed. The figure shows the voltage

waveform that was measured across the primary winding of the transformer. The

vertical axis was scaled at 10V per grid line. Notice that voltage spikes exist at the

edge of the voltage waveform. The phenomenon is caused by leakage inductance of

the transformer. This is a normal occurrence in a transformer especially in Flyback

converter. The problem can be solved by implementing an RCD-clamp across the

primary winding[15].

41

Figure 4.6: Voltage across Primary side of transformer

4.5 Output Voltage

Output voltage waveform was measured across the output. The attributes to be

looked into for output voltage are the magnitude and voltage ripple. Hardware output

voltages were then compared to calculated values and simulation. Figures shown

below are the output waveform when the duty cycle is set to 0.1, 0.2, 0.3, and 0.4.

(a) Duty cycle: 0.1, Vo=5V

(b) Duty cycle: 0.2, Vo=6.5V

42

(c) Duty cycle: 0.3, Vo=7V

(d) Duty cycle: 0.4, Vo=14V

Figure 4.7: Output voltage waveform

Output voltage ripple is low for all duty cycle, which means output capacitor

is large enough to filter the ripples. However, the output voltage magnitude is different

from calculated and simulation. This is mainly because the I-V characteristic curve of

LED which is not linear and different from the I-V characteristic curve of resistors.

When LEDs are ON, the voltage across them automatically becomes equal to required

forward voltage to turn them ON, which in this project is between 2.5V to 3.5V,

according to datasheet[11].

43

Table 3: Output voltage

Duty Cycle(D) Output Voltage()

Theory Simulation Hardware

0.1 2 1.4 5

0.2 4.5 4.2 6.5

0.3 7.7 7 7

0.4 12 10.9 14

Table 3 shows the output voltage of the hardware. When the duty cycle is 0.1,

the output voltage is 5V. As stated above, the minimum output voltage of the hardware

will be the minimum voltage required to turn ON the LED. Two LEDs are placed is

series in every parallel path in the output, therefore the required voltage is 5V. That

explains why the output voltage is 5V at duty cycle 0.1. At duty cycle 0.2 and 0.3, the

output voltage ranged around the forward voltage of the LEDs, but at duty cycle 0.4,

the output voltage becomes extremely higher than the LEDs forward voltage. At this

point, much of the voltage drops at the current limiting resistor.

4.6 LED Brightness

The HB LED brightness was observed when the hardware operates at duty

cycle 0.1, 0.2, 0.3, and 0.4. The hardware was proven successful to dim the brightness

of LEDs. The brightness of light emitted by the hardware increases with the increase

of duty cycle.

44

(a) Duty cycle: 0.1

(b) Duty cycle: 0.2

(c) Duty cycle: 0.3

(d) Duty cycle: 0.4

Figure 4.8: LED brightness

CHAPTER 5

CONCLUSION

5.1 Conclusion

In designing a hardware using Flyback converter topology, the designer needs

to understand the working principle of a Flyback converter. Flyback converter is a

unique converter if compared to the other switched mode power supply (SMPS) DC

DC converters because of its transformer. Therefore the most important knowledge to

be understood in completing the project is the knowledge of electromagnetism.

Knowledge in electromagnetism helps a lot in designing the transformer. During ON

time in Flyback converter, energy is stored in the air gap because the air has a low

magnetic permittivity. Air gap also helps reduce the risk of transformer core saturation.

In gapping the center leg of the transformer core, a file was used. The file has a very

rough space. For that reason, some part of the center leg got uneven. That is not a good

thing because magnetic flux will non-uniformly spread at the center leg, which will

then lead to a waste of energy.

There were some difficulties faced during the process of completing this

project. The first one is to learn the knowledge about electromagnetism.

Electromagnetism is a very complicated subject on its own. If we understand it well,

then the rest of the Flyback converter fundamental can be easily understood. The

second difficulty was to find the right components to be used. Components must be

chosen according to ratings and other specifications.

46

While when implementing the hardware, the hardest thing to do was to

troubleshoot a failed circuit. Things might not work because of the smallest thing, such

as a bad contact between conductors, but took one full day to be troubleshot. Also, at

one point during the implementation of hardware, a well designed and built

transformer fell to the ground and the transformer core broke into pieces. The process

of building transformer which took days to be completed, had to be started all over

again. But all that taught an unforgettable great experience.

High brightness LED behavior must be studied first before designing the circuit

because everything that we build will be respected to the output. By completing this

project, it is proven that Flyback converter is a suitable topology in implementing a

hardware of a HB LED light dimmer.

5.2 Recommendation

The first problem that seems to affect the performance of the hardware is the

voltage spikes produced across the primary winding of the Flyback converter

transformer. The problem leads to the rapid rise of temperature at MOSFET because

the voltage spikes sometimes exceed the rating of the MOSFET. One way to solve this

is by adding an RCD clamp across the primary winding. The capacitor placed in an

RCD clamp will absorb the voltage spike and the power will be dissipated by the RCD

clamp resistor. RCD clamp helps not only to absorb voltage spikes but also reduces

switching losses at MOSFET.

At the HB LED dimmer output, it is recommended that a large resistor is placed

parallel to the LEDs. When the hardware stops operating, LEDs do not turn OFF

immediately. This is because some of the energy transferred to the output is stored in

output capacitor. The output voltage will drop slowly but it cannot drop to zero because

of the LEDs minimum forward voltage. Therefore, remaining energy is stored in the

capacitor. Energy, if stored for too long in the capacitor, will cause damage to the

capacitor. Placing a high resistor across the LEDs will provide a path for discharging

47

of the capacitor. The resistor must be high enough so that it will not interrupt the

hardware performance when it operates as a current will look to flow through a path

which has the least load.

48

REFERENCE

1. Tan, D., Soraa to raise orders of LED modules, in The Star. 2013: Georgetown.

2. Arias, M., A. Vazquez, and J. Sebastian, An Overview of the AC-DC and DC-

DC Converters for LED Lighting Applications. 2012.

3. Picard, J., Under the Hood of Flyback SMPS Designs, in 2010-2011 Power

Supply Design Seminar. 2011, Texas Instruments.

4. Ghani, I.A., P.I. Khalid, and S.H. Ruslan, Electronic Circuits Teaching Module.

2011: Faculty of Electrical Engineering, Universiti Teknologi Malaysia.

5. Hart, D.W., Introduction to Power Electronics. 1997: Prentice-Hall

International.

6. Hart, D.W., Power Electronics. 2011: McGraw Hill.

7. Pressman, A.I., K. Billings, and T. Morey, Switching Power Supply Design.

2011: McGraw-Hill.

8. Khairi, M.T.b.M., DC Motor Control Using Flyback Converter, in Fakulti

Kejuruteraan Elektrik. 2011, Universiti Teknologi Malaysia.

9. Sen, P.C., Principles of Electric Machines and Power Electronics. 1997: John

Wiley & Sons.

10. Amos, R.S. and G.W.A. Dummer, Newnes Dictionary of Electronic. 1999,

Newnes.

11. General purpose rectifiers, F. Semiconductor, Editor. 2009.

12. ETD cores and accessories, Ferroxcube, Editor. 2001.

13. Regulating Pulse Width Modulators, S. Microelectronics, Editor. 2000.

14. HCPL-3180, A. Technologies, Editor. 2009.

49

15. Hren, A., J. Korelic, and M. Milanovic, RC-RCD Clamp Circuit for Ringing

Losses Reduction in a Flyback Converter. 2006.

16. Kasim, J., C. Omar, A.H. Ahmad, Modul Pengajaran Sistem Elektronik, 2009,

Universiti Teknologi Malaysia.

17. Hamzah, N., K.R. Salim, Electronics 1 Teaching Module, 2008, Universiti

Teknologi Malaysia.

18. Manitkala S., Switching Power Supplies A to Z, 2007, Newnes.

19. Mack, A.M.Jr., Demystifying Switching Power Supplies, 2005, Newnes.

20. Cathey, J.J., Electronic Devices and Circuits, 1989, McGraw Hill.

50

APPENDIX A

51

52

53

APPENDIX B

54

55

56

57

58

APPENDIX C

59

60

61

62

APPENDIX D

63

APPENDIX E

64

65

APPENDIX F

66

67

68

69

70

71

72

APPENDIX G

73

74

75

76

77

78

APPENDIX H

79

APPENDIX I