BRIDGE RECTIFIER

                    A bridge rectifier is an electronic circuit which converts A.C voltage in to pulsating D.C voltage using both half cycles of the applied A.C voltage as in the case of full wave rectifiers. It is also a full wave rectifier. Bridge rectifier avoids the usage of center tapped transformer.

Construction:

                    A bridge rectifier is shown in figure. It consists of a transformer, four semiconductor diodes and a load resistor. Because of the bridge like arrangement of diodes it is called bridge rectifier. The A.C voltage to be rectified is applied across one diagonal of the bridge through a power transformer. The load resistor is connected across the other diagonal of the bridge.

Working:

                      When an A.C voltage is applied to the input circuit the end terminals A and B of the transformer secondary becomes positive and negative alternately. During positive half cycle of the A.C input voltage terminal A is positive with respect to terminal B. In this situation diodes D1 and D3 are forward biased whereas diodes D2 and D4 are reverse biased. Therefore diodes D1 and D3 conduct and current flows through the load resistor RL as shown in figure. This current produces a voltage drop across RL.

                    During the negative half cycle of the A.C input voltage terminal B is positive with respect to terminal A. In this situation diodes D2 and D4 are forward biased whereas diodes D1 and D3 are reverse biased. Therefore diodes D2 and D4 conduct and a current flows through the load resistor RL as shown in figure. This current produces voltage drop across RL. 

                    Thus when an A.C voltage is applied to the bridge rectifier, during positive half cycle diodes D1 and D3 conduct and during negative half cycle diodes D2 and D4 conduct. However current flows through the load resistor RL in the same directions in both half cycles of the A.C input. Thus a pulsating D.C voltage is developed across the load resistor RL and we have full wave rectification. The input and output waveforms are shown in figure.

Input and output waveforms:

Advantages:

Ø  Rectification efficiency is high.

Ø  Ripple factor is low.

Ø  No center tap is needed in the transformer secondary.

Ø  D.C saturation of the transformer core is avoided.

Ø  It is highly suited for high voltage applications.

Disadvantages:

Ø  It requires four diodes instead of two.

Ø  The load resistor and the source have no common point.

Ø  Two diodes in series conduct during each half cycle of the A.C input. It increases the total voltage drop and loses.

 


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