MINI PROJECT ON

DUAL DC POWER SUPPLY

With hard efforts from:Vineet Nayan Barun Kr. JhaShiv Kundan Kumar Saurav

INTRODUCTION:

This mini project is about designing a dc power supply which instead of supplying a voltage with respect to ground would supply two different voltages, one positive and other negative at its two output pins and when required zero at the third pin.

for ex:- if we want to supply +15v & -15v to a operational amplifier we would need a dc power supply which would provide these two voltages outputs at its two terminals.

This project basically consist of four stages viz: Transformer Rectifier Filter Regulator

TRANSFO

RM-ER

BLOCK DIAGRAM

FILTER

REGULATOR

RECTIFIER

CIRCUIT DIAGRAM

DETAILED THEORY & WORKING

Some electronic circuits require a power supply with positive and negative output as well as zero volts. This is called a “dual supply” because it is like two ordinary supplies connected as shown:

Dual supplies have three outputs, for example a ±9V supply has +9V, 0V, -9V outputs

STAGE I : TRANSFORMER ONLY

We have used a 18-0-18v transformer so that we can get a maximum o/p voltage of 18V.

STAGE I : TRANSFORMER ONLY(CONT.) The practical circuit & the output

obtained on the CRO

STAGE II : TRANSFORMER +RECTIFIER

STAGE II : TRANSFORMER +RECTIFIER(CONT)

STAGE III : TRANSFORMER +RECTIFIER+FILTER

STAGE III : TRANSFORMER+RECTIFIER+FILTER(CONT.)

STAGE IV:REGULATION

Till Now-Unregulated Power Supply-> Transformer Rectifier & Filter

This type of power supply is not good: Poor Regulation (Output current varies with load)

DC output voltage varies with AC input DC output voltage varies with temperatureThese are overcome with feedback control circuit conjuction.

Also the ripple voltage is reduced.

STAGE IV:REGULATION(CONT.)

The feedback circuit to overcome the shortcomings

STAGE IV:REGULATION(CONT.)

Types of Regulator ICs(all are 3 pin) Fixed positive & negative Adjustable positive & negative

Here in our project we have used the adjustable voltage regulators.

The ICs used are LM317 and LM337

STAGE IV:REGULATION(CONT.)

STAGE IV:REGULATION(CONT.)

Fixed voltage regulated dual supply: An LM78XX or LM79XX can be used

Three terminals-input, output and ground

STAGE IV:REGULATION(CONT.)

A no. of three terminal adjustable regulators are available.

We have used LM317 and LM337 LM317

1.5A current output Voltage range—1.2V-37V

LM337 1.5A current output Voltage range— -1.2V- -37V

STAGE IV:REGULATION(CONT.)

The basic connections of the positive regulator IC.

Diode-ensures that it turns on under operating conditions.

Capacitor used to improve the transient response of the circuit.

Vo=1.25(1+R2/R1)

STAGE IV:REGULATION(CONT.)

The basic connections of the negative regulator IC.

-Vo=-1.25(1+R2/R1)

STAGE IV:REGULATION(CONT.)