# How to Make Variable DC Power Supply

How to Make Variable DC Power Supply

# Fully Regulated Variable DC Power Supply

Project by: Engineer Hafiz Yasir Qureshi NUST Pakistan

Introduction

The project “Variable DC Power Supply” plays a very important role in the laboratory functions and that is mainly to the electronics labs. As in electronics all the instruments, components work on a particular regulated dc supply, so a project which can provide this supply by converting the alternating current to direct current that too into a great range of regulated power keep its own preference. As it can produce a range of 0-30 v direct current by regulating and converting alternating current is has a vast application too. AC to DC converters generally comprise a rectifier bridge to rectify the AC current of the input line and a regulating device supplying on output of one or more regulated DC voltages. Just the simple AC is applied, simple electronic circuit is used and through potentiometer you get the desired regulated dc power supply.

### Components required to make Variable DC power supply

To make Variable DC power supply, you will required following list of components;

• Transformer 220V to 30V ,2A rating.
• Diodes
• High capacitance capacitor (1800uF)
• Small capacitors for IC.
• IC LM317
• Resistors of 500 ohms.
• 1.5A fuse.
• Probes .
• Digital voltmeter (for output reading).
• Crocodile clips.

### Construction and Working

As a student of electrical engineering I always strive for practical work along with my studies. Now I have made this adjustable DC power supply which is more economical and safe to use for any purpose which requires the DC power. The knowledge used is of basic electronics and power.
This power supply can give you DC voltage of desired value just by rotating the knob. The output voltage will be shown on the digital voltmeter of the power supply.
Initially a step down transformer reduces the voltage level from 220V to 30 V AC.then the rectifier rectifies the output voltage of the transformer.

Across the capacitor we get almost 30 V DC voltages. This voltage is applied to the input of the variable voltage regulator IC LM317 which has a variable resistor in terminal 1 which will be used as the voltage adjusting knob, because by changing the value of that resistor the output voltage of the IC varies from 2V to 30V. The formula for the output voltage of the IC by variation of resistance is given by:

for the safety of the users a fuse is also used which prevents the supply from over current flow

### Circuit diagram

Circuit made on proteus isis

### Salient Features

• Fully regulated 2V – 30V supply.
• Can be used as charger which can charge a number of phones simultaneously as current rating is about 2A.
• Can be used for charging automobile batteries.
• Priceless instrument for electronics laboratory.

### Precautions

Do connect the device which draws more than 2A current with this power supply.
Hold the clips of the probes through their insulations.
Do not short the probes while supply is ON.

### Variable DC Power Supply picture 3

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