## Regulated Power Supply – Circuit Diagrams and Working Principle

Hello folks, today we are going to learn about the regulated power supply in details. We will try to explain:

• OrdinaryÂ DC Power supply
• What is the need for a Regulated Power supply
• Working ofÂ the Regulated Power supply

## Introduction to Power Supply

We all know that many electronic circuits using tubes or transistors requires a DC power supply. We cannot use DC batteries everywhereÂ because DC batteries are costly and requireÂ replacementÂ once discharged. So in such scenarios, we need to make use of electronic circuits which can convertÂ ac supplyÂ into dc power supplyÂ using a rectifier-filter system, these kinds of electronic circuits are called as DC power supply.

Rectifier-filter circuit contains an ordinary dc power supply. The output of ordinary dc power supply remains steady as long as ac mains voltage or load is contrast. But in manyÂ electronics circuits it very important to keep the contactÂ DC power supplyÂ irrespective of variantÂ ac mains supply. There is a high possibility of circuit damage if the DC power supply is not constant. To avoid this situation, we can make use of voltage regulating devices which can keep the DC voltage at a constant level. So this combination of Voltage regulating devices with the ordinary dc power supply is called as Regulated DC power supply. Regulated DC power supply is an electrical device which produces the constant DC power supplyÂ irrespective of variantÂ ac mains supply.

## Ordinary DC Power Supply

Below circuit shows ordinary or unregulated power supply. This circuit contains a rectifier and a filter circuit. The output of a rectifier is pulsating dc because of the presence of pulsating ac component. The filter circuit is used to remove these pulsations of AC component to produce a steady dc output.

Limitations of Ordinary DC power supply

1. DC output voltage is directly proportional to the AC input voltage. If ACÂ voltage is increased, the output will increase in the same proportion, thus we won’t get constant dc output voltage.
2. DC output voltage decreases as the load current increases because of voltage drop in transformer windings, filter and rectifier circuit.

## What is the need for a Regulated Power supply?

We have already covered the limitations of an ordinary power supply.Â In an ordinary power supply, the voltage regulation is poor i.e. d.c. output voltage changes considerably with load current. Moreover, output voltage also changes due to variations in the input a.c. voltage. Thus there is a need of regulated power supply.

## Working of the Regulated Power supply

The general block diagram of regulated power supply is shown below:

## Construction and working of regulated power supply

### 1. AC supply and transformer:

A power supply is used to provide the required amount of power at specific voltage from a primary source which can be ac mains or a battery. A transformer changes the ac mains (line) voltage to a required value and it is used to step the voltage up or down. In a transistor radio it may be a step-down transformer and in a CRT it may be a step-up transformer. Transformer provides isolation from the power line. It should be used even when any change in voltage is not necessary.

### 2. Rectifier:

Full wave bridge rectifier circuit diagram

A rectifier converts ac into dc. It may be a half-wave rectifier, a full-wave rectifier using a transformer with centre-tapped secondary winding or a bridge rectifier. But the output of a rectifier may be fluctuating.

### 3. Filter:

LC filter

A filter circuit is used for smoothing out the ac variations from the rectified voltage. There are four types of filters: 1) Capacitor filter, 2) Inductor filter, 3) L-C filter and 4) R-C filter.

### 4. Voltage regulator:

A voltage regulator is necessary to maintain a constant output dc voltage by providing line regulation and load regulation. For thisÂ purpose, we can user A Zener-regulator, transistorized regulator or three terminal IC regulator. A switched mode power supply (SMPS) is used to provide large load current with negligible power dissipation in the series pass transistor.

We recommend you to please watch below lecture for a complete understanding of Regulated Power Supply:

## RC and LC Filters – Circuit Diagram, Waveforms and Working Principle

Hi friends, today we are going to learn some basic filter circuits like RC filter and LC filter.

## RC Filter

In the above figure two sections of RC filter are shown. These are connected between the input capacitor and the load resistor. The value of R should be at least 10 times greater than the capacitive reactance Xc. Therefore the ripple is dropped across the series resistors instead of across the load resistor. Each section reduces the ripple by a factor of 10. Therefore ac components are removed and at the output we get a steady dc voltage.

The main disadvantage of RC filter is the loss of dc voltage across each R. Therefore RC filter is suitable only for light loads. i.e. small load current.

## LC Filters

In this type inductor L is in series and capacitor C is in shunt with load. The choke (L) allows the dc component to pass through easily because its dc resistance R is very small. The capacitive reactance Xc is very high for dc and it acts as open circuit. All dc current passes through across which dc output voltage is obtained.

The inductive reactance XL = 2pfL is high for ac components. Therefore the ripples are reduced. Even if any ac current passes through L, it flows through the capacitor because of its low capacitive reactance.

1. In choke input filter, current flows continuously. Therefore the transformer is used more efficiently.
2. Ripple content at the output is low.
3. It is less dependent on the load current.
4. DC voltage drop across L is much smaller because its de resistance R is very small.

1. Large size and weight of inductors,
2. More cost,
3. External hold is produced by inductor.

For providing smoothest output voltage p type (capacitor input) filter can be used.

## Series Inductor Filter – Circuit diagram, Waveforms and Working Principle

This post provides an information about series inductor filter. Before going to study series inductor filter it is necessary to understand what is meant by filter circuit?

Filter Circuit – Most of the electronic circuits require a dc voltage that is constant, similar to the voltage from a battery but the rectifiers cannot provide ripple free dc voltage. They provide a pulsating dc. The circuit used for filtering or smoothing out the AC variations from the rectified voltage is called as `Filter circuit.

## Series Inductor Filter

The circuit diagram and waveforms of series inductor filter are shown below:

Series Inductor Filter – An inductor opposes any change in the current flowing through it. Whenever the current through an inductor tends to change, a back emf is induced in it. This prevents the change in current.

Inductive reactance XL = 2p* f*L. For dc, f = 0, therefore direct current easily passes through the inductor to the load. The only opposition to dc is due to internal resistance of choke. The reactance increases with frequency. Therefore AC component is opposed. The output waveform shows a large dc component and a small AC component.

The operation of a series inductor filter depends upon the current through it. The higher the current flowing through it, the better is its filtering action. An increase in load current reduces the ripples.