RECTIFIERS

“Rectifiers are the circuit which converts ac to dc”

Rectifiers are grouped into tow categories depending on the period of conductions.
1. Half-wave rectifier
2. Full- wave rectifier.

Half-wave rectifier
The circuit diagram of a half-wave rectifier is shown in fig below along with the I/P and O/P waveforms.

Half wave rectifier (i) Circuit diagram (ii) waveforms

• The transformer is employed in order to step-down the supply voltage and also to prevent from shocks.

• The diode is used to rectify the a.c. signal while , the pulsating d.c. is taken across the load resistor RL.

• During the +ve half cycle, the end X of the secondary is +ve and end Y is -ve . Thus , forward biasing the diode. As the diode is forward biased, the current flows through the load RL and a voltage is developed across it.

• During the –ve half-cycle the end Y is +ve and end X is –ve thus, reverse biasing the diode. As the diode is reverse biased there is no flow of current through RL thereby the output voltage is zero.

Full-wave rectifier

Full-wave rectifier are of two types

1. Centre tapped full-wave rectifier
2. Bridge rectifier

Centre tapped full –wave rectifier

Centre tapped Full wave rectifier (i) Circuit diagram (ii) waveforms

• The circuit diagram of a center tapped full wave rectifier is shown in fig. 2.6 above. It employs two diodes and a center tap transformer. The a.c. signal to be rectified is applied to the primary of the transformer and the d.c. output is taken across the load RL.

• During the +ve half-cycle end X is +ve and end Y is –ve this makes diode D1 forward biased and thus a current i1 flows through it and load resistor RL.Diode D2 is reverse biased and the current i2 is zero.
• During the –ve half-cycle end Y is +Ve and end X is –Ve. Now diode D2 is forward biased and thus a current i2 flows through it and load resistor RL. Diode D1 is reversed and the current i1 = 0.

• Since, each diode uses only one-half of the transformer secondary voltage the d.c. output is comparatively small.
• It is difficult to locate the center-tap on secondary winding of the transformer.
• The diodes used must have high Peak-inverse voltage.

Bridge rectifier

Full wave bridge wave rectifier (i) Circuit diagram (ii) waveforms.

• The circuit diagram of a bridge rectifer is shown above. It uses four diodes and a transformer.

• During the +ve half-cycle, end A is +ve and end B is –ve thus diodes D1 and D3 are forward bias while diodes D2 and D4 are reverse biased thus a current flows through diode D1, load RL ( C to D) and diode D3.

• During the –ve half-cycle, end B is +ve and end A is –ve thus diodes D2 and D4 are forward biased while the diodes D1 and D3 are reverse biased. Now the flow of current is through diode D4 load RL ( D to C) and diode D2. Thus, the waveform is same as in the case of center-tapped full wave rectifier.