Question

Draw a neat diagram of a full-wave rectifier and explain it’s working.

Answer 1

A device or a circuit which rectifies both halves of each cycle of an alternating voltage is called a full-wave rectifier.

Electric circuit: The alternating voltage to be rectified is applied across the primary coil (P₁P₂) of a transformer with a center-tapped secondary coil (S₁S₂). The terminals S₁ and S₂ of the secondary are connected to the two p-regions of two junction diodes D₁ and D₂, respectively. The center-tap Tis connected to the ground. The load resistance RL is connected across the common n-regions and the ground.

                     Full-wave rectifier circuit

P₁P₂, S₁S₂ - Primary and secondary transformer,

T - Centre-tap on secondary,

D₁, D₂ - Junction diodes, 

R_L - Load resistance,

I_L - Load current,

V_i - AC input voltage,

V_o - DC output voltage  

Working: During the one-half cycle of the input, terminal S₁ of the secondary is positive while S₂ is negative with respect to the ground (the centre-tap T). During this half cycle, diode D₁ is forward biased and conducts, while diode D₂ is reverse biased and does not conduct. The direction of current I_L through R_L is in the sense shown.

Voltage waveforms for a full-wave rectifier
(a) input (b) output

During the next half-cycle of the input voltage, S₂ becomes positive while S, is negative with respect to T. Diode D₂ now conducts sending a current I_L through R_L in the same sense as before. D₁ now does not conduct. Thus, the current through R_L flows in the same direction, i.e., it is unidirectional, for both halves or the full wave of the input. This is called full-wave rectification. The output voltage has a fixed polarity but varies periodically with the time between zero and a maximum value. The above figure shows the input and output voltage waveforms. The pulsating de output voltage of a full-wave rectifier has twice the frequency of the input.