Variable Power Supply

1.1 INTRODUCTION

A power supply is a device that supplies electrical energy to one or more electric loads. The term is most commonly applied to devices that convert one form of electrical energy to another. A regulated power supply is one that controls the output voltage or current to a specific value, the controlled value is held nearly constant despite variations in either load current or the voltage supplied by the power supply's energy source. Variable power supplies are common laboratory and service shop test equipment, allowing the output voltage to be adjusted over a range.

1.2 SCOPE

One of the basic building blocks of electronics project is building DC power supplies from an AC source of 110 v ac or 220 v ac. The common DC voltages that are required to power up the devices are generally in the range of 3 v dc to 30 v dc. Typically the fixed types of DC voltages are 5 v, 9 v, 12 v, 15v and 18 v dc. With the advancement of technology, many devices are using 1.8 v dc, 3.7 v dc, 6.7 v dc etc these days. So the need of variable power supply is most in today’s world.

2.1 GENERAL BLOCK DIAGRAM & ITS DESCRIPTION

Fig. 2.1 Block Diagram of Variable Power Supply

Figure 2.1 shows the general block diagram of the variable power supply system. It consists of mainly four blocks i.e. Transformer, Rectifier, Smoothing and Regulator.

2.1.1 TRANSFORMER

Transformer is used to step-down the mains AC voltage. Mains supply (230 v AC) is the input of the transformer. This voltage is step down by transformer as per its rating.

2.1.2 RECTIFIER

There are several ways of connecting diodes to make a rectifier to convert AC to DC. The bridge rectifier is the most important and it produces full-wave varying DC.