Power Supply

 Introduction and Block Diagram of Regulated Power Supply

Introduction

•      The specifications of ac voltage is 230 Volt, 50 Hz.

•      For operations of most of devices in electronic equipment like radio, television, computer, tape recorder, signal generator, mobile phone D.C. Voltage is required.

•      Dry cells and batteries are D.C. Sources. They have an advantage of being portable and providing ripple free D.C. voltage.

•      However, as these sources are chemical reaction dependent, they need frequent replacement or maintenance. Also, as each dry cell or battery provides low voltage, number of cells and batteries are required to get higher voltages, hence they become expensive for the appliances.

•      For rechargeable batteries, it is necessary to charge it periodically for better results.

•      In order to overcome this, all electronic equipment include a circuit that converts A.C. voltage of mains supply into desired D.C. voltage. This part of the equipment is called power supply.

•      The power supply consists of a transformer, rectifier, filter and regulator.

•      Different applications need different type of power supplies, e.g. a battery charger needs only a D.C. source with high current, while for computer a well regulated short circuit protected power supply is needed.

 

■       Block Diagram of Regulated Power Supply

■       Power Supply is needed in all of the electronic gadgets, instruments and appliances.

■       The block diagram of power supply is shown in fig.




■       As shown in the block diagram, power supply is used to derive DC voltage of the level 3 to 24 volt as per need from AC 230 volt mains power supply.

■       The various stages need to build power supply are (i) transformer, (ii) Rectifier, (iii) Filter circuit, (iv) Voltage regulator. The need and function of each block is discussed below.

■       Transformer (X'mer) :

It’s job is either step up or step down the AC supply voltage. It also provides isolation from the supply line ad hence power supply becomes shockproof, hence the quality of X’mer is very important. The step down X’mer converts 230V AC voltage level to lower level ac of the required valued generally upto18 volt, 12 volt, 9 volt, 6 volt, 3 volt etc.

■       Rectifier :

■       Diode circuit is used as rectifier, which converts AC voltage into DC voltage necessary to drive electronic instruments, gadgets, appliances or to replace batteries.

■       According to Various needs and stability of DC level, half wave, full wave or bridge rectifier circuits are used in a power supply.

■       Filter Circuit :

■       After conversion of AC into DC through rectifier some ripple or AC voltage level occur at output which is to be suppressed by using filter circuit.

It bypasses or removes any ripple of AC voltage level that occurs at the output of rectifier stage.

It provides smooth DC level output which is necessary to drive electronic circuits to operate without errors.

■       Voltage Regulator :

To make the output voltage constant, irrespective of the changes in line voltage, load current and temp, voltage regulator circuits are used.

 

■       Fixed Voltage Power Supply

■       Power supplies are of two types, unregulated or ordinary power supply and regulated power supply.

■       Fixed voltage power supply are designed to get a particular value of D.C. output voltage at specified current for specific applications.

■       E.g. mobile battery charger, radio receiver, D.C. adaptor, rechargeable battery charger, digital circuits (+5Volt fixed) or laptop battery charger.




Working :

Step down transformer converts 230 volt A.C., 50Hz signal into smaller A.C. voltages.

Then rectifier converts this ac voltage into dc voltage using HWR, FWR or BWR.

Simple RC filter is used to remove the ripple voltage.

This is the unregulated or ordinary power supply.

But in the equipment’s where a well stabilized power source is needed, ordinary unregulated power supply is of no use.

e.g. CRO, signal generators, medical equipment like pace maker, laboratory power supplies are some of the equipment where D.C. regulated power supplies are needed.

 

Fixed Voltage Regulated power Supply:




A D.C. power supply which maintains the output voltage constant, irrespective of A.C. mains fluctuations or load variations is known as regulated D.C. power supply.

Above fig. shows the block diagram for regulated fixed voltage power supply




A regulated power supply consists of an ordinary power supply (consisting of step down transformer, rectifier, filter) and voltage regulating device as shown above.

Output of regulated power supply is stabilized or made constant by the voltage regulator. The output voltage made constant irrespective of the changes in line voltage, load current, temp. etc.

A Zener diode is simple shunt voltage regulator, which is used as a regulator in most of the regulated fixed voltage power supplies.

In some of the commercial, regulated power supplies, voltage regulator IC’s are used.



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