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ABSTRACT
Transformer-less power supply is an electronic device that supplies electric energy to an electrical load without a transformer for stepping up or down. The primary function of a power supply is to convert one form of electrical energy to another. This is done by the use of reactance to limit the current, rectify the voltage with a diode, regulate the voltage with a zener, and use a large electrolytic capacitor to filter out the ripples. There are several ways to convert an AC voltage at a wall receptacle into the DC voltage required by a microcontroller. Traditionally, this has been done with a transformer and rectifier circuit. There are also switching power supply solutions, however, in applications that involve providing a DC voltage to only the microcontroller and a few other low-current devices, transformer based or switcher-based power supplies may not be cost effective. Transformer-less power supplies thus, has a distinct advantage in cost as well as in size. The disadvantages of using a transformer less power supply are: 0ne Low current supply and two No solution from the AC line voltage. Project is very much useful where: the efficiency is not given much importance. The main advantage of this project is very low cost components, and small in size. This circuit is not suitable for high current drawing circuit like relay boards.
TABLE OF CONTENTS
TITLE PAGE
ABSTRACT ii
AKNOWLEDGEMENT iii
DECLARATION————————————————————————————iv
DEDICATION v
CERTIFICATION vi
TABLE OF CONTENTS vii
LIST OF FIGURES ix
LIST OF TABLES x
CHAPTER ONE 1
1.0 INTRODUCTION 1
1.1 AIM OF THE PROJECT 2
1.2 PURPOSE OF THE STUDY 2
1.3 SCOPE OF THE PROJECT 3
1.4 PROBLEM STATEMENT 3
1.5 SIGNIFICANCE OF THE PROJECT 3
1.6 ASSUMPTIONS OF THE PROJECT 4
1.7 LIMITATIONS OF THE PROJECT 5
1.8 DEFINITIONS OF TERMS 5
1.9 ORGANIZATION OF THE PROJECT 6
CHAPTER TWO 7
LITERATURE REVIEW 7
2.1 TRANSFORMER-LESS LOW COST DC POWER SUPPLY; 7
RESISTIVE & CAPACITIVE 7
2.2 CAPACITIVE TRANSFORMER-LESS POWER SUPPLY 8
2.2.1 THE CAPACITOR 8
2.2.2 X-RATED CAPACITORS 9
2.3 RESISTIVE TRANSFORMERS-LESS POWER SUPPLY 10
CHAPTER THREE 11
METHODOLOGY 11
3.1 BACKGROUND 11
3.3 ANALYSIS OF THE CIRCUIT COMPONENT 13
3.3.2 RECTIFICATION 14
3.3.3 DC SMOOTHING CAPACITORS 15
3.3.4 THE ZENER DIODE FOR VOLTAGE REGULATOR 15
3.4 TRANSFORMER-LESS AND TRANSFORMER POWER SUPPLY 19
3.5 ADVANTAGES AND DISADVANTAGES OF TRANSFORMER-LESS POWER SUPPLY. 20
CHAPTER FOUR 21
SYSTEM DESIGN, DEVELOPMENT AND IMPLEMENTATION 21
4.1 CIRCUIT OF A TRANSFORMER-LESS POWER SUPPLY 21
4.2 X RATED CAPACITOR 22
4.3 BRIDGE RECTIFICATION 24
4.4 DC SMOOTHING 26
4.5 VOLTAGE REGULATOR 26
4.5.1 POWER RATING 27
4.6 LED INDICATOR 28
4.7 THE RESISTOR 30
4.7.1 THE COLOUR CODES 30
CHAPTER FIVE 33
CONCLUSION AND RECOMMENDATION 33
5.1 MAINS ELECTRICITY IS VERY DANGEROUS 34
5.2 CONCLUSION 36
5.3 RECOMMENDATION 37
APPENDIX 38
REFERENCES 39
CHAPTER ONE
1.0 INTRODUCTION
A power supply is an electronic device that supplies electric energy to an electrical load. The primary function of a power supply is to convert one form of electrical energy to another and as a result, power supplies are sometimes referred to as electric power converters. Some power supplies are discrete, standalone devices whereas others are built into larger devices along with their loads. Examples of the latter include power supplies found in desktop computers and consumers electronic devices. Every power supply may obtain the energy it supplies to its load, as well as any energy it consumes while performing that task from an energy source. Depending on its design, a power supply may obtain energy from various types of energy sources, including electrical energy transmission systems, energy storage devices such as batteries and fuel cells electromechanical systems such as generators and alternators, solar power converters or another power supply. All power supplies have a power input, which receives energy from the energy source and a power output that delivers energy to the load. In most power supplies the power input and output consist of electrical connectors or hardwired circuit connections, though some power supplies employ wireless energy transfer inline of galvanic connections for the power input or output.
Transformer-less power supplies provide a low cost alternative to transformer-based and switcher-based power supplies. The two basic types of transformer-less power supplies are resistive and capacitive.
1.1 AIM OF THE PROJECT
The aim of this work is to provide the required DC power to the load using an AC supply at the input without using transformer. Different applications require different attributes, but more often than not these days DC power supplies provide an accurate output voltage, this is regulated using electronic circuitry (such as zener diode) so that it provides a constant output voltage over a wide range of output loads.
1.2 PURPOSE OF THE STUDY
The purpose of this project is to design and construct a circuit, which will eliminate the use of transformer in the supply of power to an electronic device (circuit); therefore overcoming the disadvantages of the transformer. The designed circuit will use a semi-conductor device which consumes less power and space to maximize the life and efficiency of the electrical appliances. The system would be robust and compact in size. Reduction in cost of equipment, as well as power consumption is highly anticipated.
1.3 SCOPE OF THE PROJECT
This application note will discuss capacitive transformer-less power supply with a focus on the following:
1) A circuit analysis of the supply.
2) The advantages and disadvantages of transformer-less power supply.
3) Additional considerations including safety requirements and tradeoffs associated with half-bridge versus full-bridge rectification.
1.4 PROBLEM STATEMENT
The conversion of an AC to DC voltage with the use of a transformer to step down the main power supply to a lower voltage, so that the devices can use it. Generally, the transformer makes the system bulky, introduces power loss which is dissipated in the form of heat and generates a looming noise during its operation. And the transformer-based circuits are very cooperative to build. It is a result of these that the newly designed transformer-less power supply was constructed. It is cost effective and greatly reduced the size of the system.
1.5 SIGNIFICANCE OF THE PROJECT
The output voltage level by varying the value of the zener diode. Its cost is lesser than transformer power supply. It is more portable than transformer power supply.
Every electronic circuit inevitably requires a DC power supply to operate this voltage is basically derived from our domestic AC mains outlet and is stepped down to the required safe level, suitable for the connected circuit. Normally, we utilize an AC – DC adapter (battery eliminator) for the purpose. These adapters fundamentally consist of three important components required for the above conversion via – the transformer, the Bridge Rectifier and the filter capacitor. The transformer is used to step down applied AC mains through electromagnetic induction.
The above process of obtaining DC from AC mains voltage is very efficient, invincibly used everywhere and has become quite a standard practice. However, since the size of transformers cannot be compromised, circuits employing these kinds of power supplies tend to become quite heavy and bulky.
The circuits described here are all intended to be used for low power applications (100MA max), but that’s not a disadvantage as most electronic circuit don’t require current above that figure.
1.6 ASSUMPTIONS OF THE PROJECT
Transformer-less power supply is cheaper in production than transformer-based power supply.
Transformer-less power supply is smaller in size than transformer-based power supply; thereby occupying less space.
Transformer-less power supply eliminate power loss; that is associated with transformer based power supply.
Transformer-less power supply has isolation from the mains or wall sources; while transformer-less power supply don’t.
Transformer-less power supply is considered bas replacement for regular transformer power supply; as a result of its drawback (non-isolation from AC mains).
A simple modification can eliminate this drawback and totally convert it to an almost ideal transformer-less power supply.
1.7 LIMITATIONS OF THE PROJECT
The main limitation of transformer-less power supplies is that they don’t offer isolation from the HV line and present more of a safety issue.
Therefore also few limitations associated with the design, particularly, the capacitors.
The drawback of the capacitor power supply includes:
- Low current output with a capacitor power supply, maximum output current available will be 100mA or less, so it is not ideal to run heavy current inductive loads.
- Output voltage and current will not be stable of the AC input varies.
1.8 DEFINITIONS OF TERMS
MOSFET: Metallic oxide semi-conductor field effect transistor.
PCB: Project Circuit Board.
LED: Light Emitting Diodes.
DC Voltage: Direct Current Voltage.
AC mains Voltage: Alternating Current Voltage (wall outlet source).
Transformer-less Power Supply System: A power supply system that uses other ways of stepping down the AC mains voltage.
Smps: Switch Mode Power Supply.
Capacitive transformer-less power supply system: A power supply system that uses capacitor (X rated) to drop down the AC mains voltage.
Resistive transformer-less power supply system: A power supply system that uses resistor (high value) to drop down the AC mains voltage.
X-rated Capacitor: A capacitor designed mainly for AC voltage; it is used to drop down the AC voltage.
Switcher-Based power supply: A power supply system that uses Inductor/MOSFET/Controller to drop-down the AC mains voltage.
1.9 ORGANIZATION OF THE PROJECT
The remainder of the study is divided into four other chapters; chapter two titled the Literature review; examines the previous studies in existing transformer-less power supply system; types and operation.
Chapter three titled methodology – system analysis; will focus on the operation of the proposed circuit and its outcomes. Chapter four titled system design and implementation, will consist of the detailed components used in the circuit and its calculation. Finally the chapter five will sum up the study and some recommendations.
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