SIX MONTHS INDUSTRIAL TRAINING REPORT

ON

“DESIGNING OF POWER SUPPLY

USING FLY-BACK TECHNOLOGY”

FOR

THE PARTIAL FULFILLMENT OF ACCOMPLISHMENT OF BACHELOR’S DEGREE IN

ELECTRONICS AND COMMUNICATION ENGINEERING.

RAM DEVI JINDAL COLLEGE OF ENGINEERING

AND TECHNOLOGY LALRU

SUBMITTED TO:-

Er. Manisha sharma SUBMITTED BY:-

Ateeb Aijaz Wani

Electronics & Communication Roll No- 100560417137

CONTENTS

Introduction………………………………………………………3

Types of DC Power Supply…………………………………….4

Converter Selection……………………………………………..8

What is Fly-back and Why it is used………………………….8

Design Consideration………………………………………….10

Design Calculation……………………………………………..19

Selection Criteria (MOSFET & PWM IC)…………………….23

IC-3845 Design Consideration……………………………….24

Circuit Diagram………………………………………………….27

Observations……………………………………………………..28

Losses in MOSFET………………………………………………30

Calculation………………………………………………………..31

Power supply circuit…….……………………………………32-33

INTRODUCTION

Description

Power supply using fly-back converter is power supply that provides the multiple output voltage for the various operation. It is designed to provide the regulated output voltage within the varying specified range of input voltage.

Design Requirements

Design an isolated 8.3W power supply that can provide multiple output voltage from an input voltage ranging from 10-100VDC. The system has the switching frequency of 68KHz. The maximum output voltage ripple is 200mV.

Output Voltage 1 (VO1) = 12±0.5V

Output Voltage 2 (VO2) = 5±0.1V

Output Voltage 3 (VISO) = 5±0.1V

Types of DC Power Supplies

DC Power Supply

DC-DC converters are power electronics circuit that converts a dc voltage to the different dc voltage level, providing a regulated output. The efficient method of providing electrical isolation between input and output of a dc-dc converter is to use a transformer in the switching scheme. With the use of multiple transformer windings, switching converters can be designed to provide multiple output voltages.

Types of isolated supplies:

· Fly-back converter

· Forward converter

· Push-Pull converter

· Half Bridge converter

· Full Bridge converter

Fly-back Converter

The fly-back is the buck boost converter with the inductor split to form a transformer, so that voltage ratios are multiplied with the additional advantage of isolation.

In the ON-state, the energy is transferred from the input voltage source to the transformer (the output capacitor supplies energy to the output load).

In the OFF-state, the energy is transferred from the transformer to the output load (and the output capacitor)

Forward converter:

The forward converter is a DC/DC converter that uses a transformer to increase or decrease the output voltage (depending on the transformer ratio) and provide galvanic isolation for the load .The forward converter (which is based on a transformer) does not store energy during the conduction time of the switching element - transformers cannot store a significant amount of energy unlike inductors. Instead, energy is passed directly to the output of the forward converter by transformer action during the switch conduction phase.

The use of the forward converter constrains the maximum output voltage by the transformer turns ratio

NS/NP:

VOUT = D*NS/NP*VIN

Where, D is the pulse width modulator duty cycle.

Push-Pull converter:

A push–pull converter is a type of DC-to-DC converter, a switching converter that uses a transformer to change the voltage of a DC power supply. The distinguishing feature of a push-pull converter is that the transformer primary is supplied with current from the input line by pairs of transistors in a symmetrical push-pull circuit. The transistors are alternately switched on and off, periodically reversing the current in the transformer. Therefore current is drawn from the line during both halves of the switching cycle. Push-pull converters have steadier input current, create less noise on the input line, and are more efficient in higher power applications.

Benefits and Limitations:

Fly-back:

Benefits-The fly-back converter, having a low parts count, is a simple circuit to implement and is very popular for low-power applications. The fly-back converter is used most often for an output power of 10 W or less

Limitations- The main disadvantages are that the transformer core must be made large as power requirements increase, and the voltage stress across the switch is high (2Vs). Typical applications can go up to about 150 W.

Forward:

Benefits-The forward converter is a popular circuit for low and medium power levels, up to about 500 W. It has one transistor as does the fly-back, but it requires a smaller transformer core.

Limitations-Disadvantages are high voltage stress for the transistor and the extra cost of the filter inductor. The double-ended forward converter can be used to reduce the switch voltage stress, but the drive circuit for one of the transistors must be floating with respect to ground.

Push-Pull:

Benefits-The push-pull converter is used for medium to high power requirements, typically up to 1000 W. Advantages include transistor drive circuits that have a common point and a relatively small transformer core because it is excited in both directions.

Limitations- Disadvantages include a high voltage stress for the transistors and potential core saturation problems caused by a dc imbalance in non-ideal circuits.

Half-bridge:

Benefits- The half-bridge converter is also used for medium power requirements, up to about 500 W, and has some of the same advantages as the push-pull. The voltage stress on the switches is limited to Vs.

Full-Bridge:

Benefits-The full-bridge converter is often the circuit of choice for high-power applications, up to about 2000 W. The voltage stress on the transistors is limited to Vs.

Limitations-Extra transistors and floating drive circuits are disadvantages.

Converter Selection

Any power supply circuit can be designed for any application, depending on how much the designer is willing to spend for components and control circuitry. In practice, some circuits are much more suited to particular applications than others.

In our design consideration, we select the fly-back converter for designing power supply.

What is Fly-back converter and why is it used?

Fly-back converter: