Bridge Rectifier

Bridge Rectifier

During the positive half cycle of the input ac, A becomes +ve and B becomes -ve. Hence the diode D1 and D3 becomes forward biased and D2 and D4 becomes reverse biased. Hence D1 & D3 act as short circuit and D2 & D4 act as open circuit. The current flows through the load resistor R in the direction A-D1-a-b-D3-B.

During the negative half cycle of the input ac, A becomes -ve and B becomes +ve. Hence the diode D2 and D4 becomes forward biased and D1 and D3 becomes reverse biased. Hence D2 & D4 act as short circuit and D1 & D3 act as open circuit. The current flows through the load resistor R in the direction B-D2-a-b-D4-A.

It can be seen that both during +ve half cycle and -ve half cycle, the current through the load resistor R flows from a to b. Hence output voltage will be always positive

Here all the diodes are assumed as ideal ones. 

If silicon diodes are used the maximum output voltage will be reduced to Vm-1.2 Volt. ie 0.6 V will be dropped across two diodes in each half cycle (0.6 + 0.6 )

Center Tap Full Wave Rectifier

Full Wave Rectifier

There are two types of Full wave rectifiers

• Center Tap Full wave rectifier
• Bridge Rectifier 

Center Tap Full Wave Rectifier

The center tap transformer split the primary input ac signal into two equal but opposite phase ac signals. 

During the +ve half cycle of the input ac, the diode D1 is forward biased and diode D2 is reverse biased. Hence D1 will conduct and D2 will not conduct. The current flows in the direction D1 - RL - Ground. 

During the -ve half cycle of the input ac, the diode D2 is forward biased and diode D1 is reverse biased. Hence D2 will conduct and D1 will not conduct. The current flows in the direction D2 - RL - Ground. 

It can be seen that in both the half cycles the output current flows through the load resistor RL in the same direction and hence the circuit is working as a full wave rectifier.

The PIV of this rectifier is 2Vm   (Vm is the maximum secondary voltage induced)

Output frequency = 2fin  Twice that of input frequency