Bridge Rectifier

What is Bridge rectifier?

Bridge rectifier is a type of full wave rectifier which uses four diodes and converts input alternating current (AC) into direct current (DC) efficiently.

Advantage of  Bridge rectifier :

Rectifiers are semiconductor devices which converts the Alternating current (AC) into direct current (DC). In half wave rectifier only half cycle of AC input is converted into DC and the other half is wasted. 

In Center tapped full wave rectifier both positive and negative cycle of the AC is converted into DC and with the help of capacitor filter smooth DC output is obtained. 

But the drawback of center tapped full wave rectifier is the center tapped transformer is costly. So to lower the cost, instead of center tapped transformer, four diodes are used. This is called bridge rectifier.

Construction of Bridge rectifier:

 

Bridge rectifier Circuit

The bridge rectifier consists of four diodes D1,D2,D3,D4 and a load resistance. The AC is given across the terminal A and B and the DC output is obtained across C and D.

Working of Bridge rectifier:

Working of bridge rectifier during positive half cycle

 

During positive half cycle of the input alternating current the terminal A becomes positive and terminal B becomes negative. 

So the diodes D1 and D3 will be forward biased and diodes D2 and D4 will be reverse biased. The direction of the current flow will be A to D1 to D to RL to C to D3 and B.

Working of bridge rectifier during negative half cycle

 

During negative half cycle of the input alternating current the terminal B becomes positive and terminal A becomes negative. 

So the diodes D1 and D3 will be reverse biased and diodes D2 and D4 will be forward biased. The direction of the current flow will be B to D4 to D to RL to C to D2 and A.

The output is received across the load resistance. The direction of the current across the load resistance is same.

Output waveform of the Bridge rectifier:

Output waveform of a bridge rectifier

 

During positive cycle diodes D1 and D3 are forward biased and pulsating DC for the positive half cycle is obtained. In the same way during negative half cycle of the input AC the diodes D2 and D4 are forward biased and pulsating DC output for negative half cycle is obtained. 

So by using four diodes both the positive and negative half cycle of the AC is converted into DC with ripples is obtained.

Bridge rectifier with Smoothing capacitor:

Bridge rectifier with smoothing capacitor

 

A capacitor is added in parallel with the load resistance Initially the capacitor is uncharged. Then slowly capacitor charges and attains maximum when the input voltage reaches its maximum. 

When the input voltage drops the capacitor starts discharging very slowly and it does not discharges completely, again it starts charging. 

Bridge rectifier output waveform with capacitor filter

 

So by using soothing capacitor, unnecessary ripples can be removed from the generated output. Thus pure DC output is obtained.

Bridge Rectifier calculations:

Bridge rectifier calculations

Advantages:

•      There is no need of center tapped transformer

•      Output terminal is not grounded

•      It is used in high voltage applications

•      It is less costly than other full wave rectifiers

 

Disadvantages:

•      Poor voltage regulation

•      It needs four diodes

•      Internal resistance voltage drop is high

 

Applications:

•    Because of its low cost, it is widely used in power supply circuits

•      Used in electric welding

•      Used in modulation of radio signals