An Overview Of An Ac-Dc Step Down Converter

ABSTRACT

This project is on ac/dc step down converter. This is a power supply is basically for Production of low voltage DC power supply from AC. Here a transformer is used to step down the AC mains input voltage to the required DC level.

A bridge rectifier configuration is used to rectify the low voltage AC into DC and is further smoothed by a high value electrolytic capacitor.

This DC is fed to an electronic circuit which regulates the voltage into a constant level and is applied to the load, where the energy is stored through an internal process of chemical reaction.

TABLE OF CONTENTS

 TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWLEDGEMENT

ABSTRACT

TABLE OF CONTENT

CHAPTER ONE

• INTRODUCTION
• DEFINITION OF THE PROJECT
• AIM/OBJECTIVE OF THE PROJECT
• SIGNIFICANCE OF THE PROJECT
• ADVANTAGES OF THE PROJECT
• LIMITATION OF THE PROJECT
• APPLICATION OF THE PROJECT
• OBJECTIVE OF THE PROJECT
• PROJECT ORGANIZATION

CHAPTER TWO

LITERATURE REVIEW

2.0      LITERATURE REVIEW

2.1      REVIEW OF REGULATED POWER SUPPLY

2.2     REVIEW OF POWER SUPPLY CHARACTERISTICS

2.3      REVIEW OF GENERAL APPLICATION OF POWER SUPPLY APPLICATIONS

2.4       REVIEW OF TYPES OF POWER SUPPLY
CHAPTER THREE

3.0      CONSTRUCTION METHODOLOGY

3.1      BLOCK DIAGRAM OF THE SYSTEM

3.2      CIRCUIT DIAGRAM

3.3      CIRCUIT DESCRIPTION

3.4      SYSTEM OPERATION

3.6     COMPONENTS LIST

3.7     DESCRIPTION OF MAJOR COMPONENTS USED

CHAPTER FOUR

4.0       RESULT ANALYSIS

4.1      CONSTRUCTION PROCEDURE AND TESTING

4.2      ASSEMBLING OF SECTIONS

4.3      CONSRUCTION OF THE CASING

4.4     TESTING

4.5     INSTALLATION OF THE COMPLETED DESIGN

CHAPTER FIVE

• CONCLUSIONS
• RECOMMENDATION
• REFERENCES

 CHAPTER ONE

1.0                                                        INTRODUCTION

Power supply 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, stand-alone devices, whereas others are built into larger devices along with their loads. Examples of the latter include power supplies found in desktop computers and consumer electronics devices.

Every power supply must 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 a 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 in lieu of galvanic connections for the power input or output. Some power supplies have other types of inputs and outputs as well, for functions such as external monitoring and control.

Ac/dc step down converter supplies electric energy to an electrical load is built with  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 use a reactance to limit the current, rectify the voltage with a diode, regulate the voltage with a voltage regulator ic, and use a large electrolytic capacitor to filter out the ripples.

AC-DC step down converter solutions can be designed to meet almost every conceivable application requirement in terms of power, performance, efficiency, communications, protection, size, approvals compliance, and cooling requirements.

To obtain a complete circuit for this work, the circuit is mainly composed of the:

• Input transformer:   The input transformer is used to transform the incoming line voltage down to the required level for the power supply. Typically the input transformer provides a step down function. It also isolates the output circuit from the line supply.
• Rectifier:   The power supply rectifier converts the incoming signal from an AC format into raw DC. Either half wave or more commonly full wave rectifiers may be used as they make use of both halves of the incoming AC signal.
• Smoothing:   The raw DC from the rectifier is far from constant falling to zero when the AC waveform crossed the zero axis, and then rising to its peak. The addition of a reservoir capacitor here fills in the troughs in the waveform, enabling the next stage of the power supply to operate. Large value capacitors are normally used within this stage.
• Regulator:   This stage of the power supply takes the smoothed voltage and uses a regulator circuit to provide a constant output virtually regardless of the output current and any minor fluctuations in the input level.

 Safety First!
When the AC source is a mains power socket, great care must be taken to ensure an implementation is safe to use. Without exception, this subsystem should be designed and implemented by a qualified expert. If possible, use a preapproved off-the-shelf plug pack.

Compliance is Compulsory!
When you plug in anything to a mains plug socket, it must comply with legal certification standards in the country it will be used in. More than this, it must have been tested and certified to do so – an expensive process. This is to ensure it is safe, does not interfere with other people or contribute noise to the AC main power lines.

1.1                       DEFINITION OF AC/DC CONVERTER

Electric power is transported on wires either as a direct current (DC) flowing in one direction at a non-oscillating constant voltage, or as an alternating current (AC) flowing backwards and forwards due to an oscillating voltage. AC is the dominant method of transporting power because it offers several advantages over DC, including lower distribution costs and simple way of converting between voltage levels thanks to the invention of the transformer. AC power that is sent at high voltage over long distances and then converted down to a lower voltage is a more efficient and safer source of power in homes. Depending on the location, high voltage can range from 4kV (kilo-volts) up to 765kV. As a reminder, AC mains in homes range from 110V to 250V, depending on which part of the world you live it. In Nigeria the typical AC main line is 220V.

1.2                                                   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 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 voltage regulator) so that it provides a constant output voltage over a wide range of output loads.

1.3                                          APPLICATION OF THE PROJECT

• This device is used in powering of electronics appliances such as radio, DVD.
• It is used in cellphone charger
• It is used in Solar energy system
• It is used in vehicles
• It is used in transmitters

1.4                                         SIGNIFICANCE OF THE PROJECT

• The output voltages can be use to achieve different voltage level by varying the value of the voltage regulator.
• Its cost is lesser than transformer power supply

1.5                                           LIMITATION OF THE PROJECT

• Ac-dc power supply can cause several serious problems; add hum to your signal, cause interference to your neighbors, low current rating, unstable operation under RF field.
• When loaded with a load more than the output voltage can damage the device.

1.6                             OBJECTIVE OF THE PROJECT

The objective of this work is to:

1. To reduce a high voltage ac supply (say mains power) to a lower voltage as required by some appliance or circuit
2. To provide a HIGH CURRENT at a lower voltage (again, say, from a mains power supply) for example, to use for welding.
3. To ‘match’ a high impedance output from a solid state or ‘tube’ amplifier to a low impedance speaker or headphones.
4. To provide – for safety – isolation of your lower voltage ac supply from the mains power supply.

1.7                                BENEFIT OF THE PROJECT

This device is used for providing the required supply to the electrical and electronic circuits or kits. There are many advanced automatic voltage regulators capable of adjusting the output voltage automatically based on the criteria of application.

1.7                                        PROJECT WORK ORGANIZATION

The various stages involved in the development of this project have been properly put into five chapters to enhance comprehensive and concise reading. In this project thesis, the project is organized sequentially as follows:

Chapter one of this work is on the introduction to a ac-dc power supply. In this chapter, the background, significance, objective limitation and problem ac-dc power supply were discussed.

Chapter two is on literature review of ac-dc power supply. In this chapter, all the literature pertaining to this work was reviewed.

Chapter three is on design methodology. In this chapter all the method involved during the design and construction were discussed.