Question

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

With the help of a circuit diagram, explain the working of the full-wave rectifier.

With a neat circuit diagram, explain the working of a full wave rectifier. Draw input-output waveforms.

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 = Primary transformer,

S₁S₂ = 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 DC output voltage of a full-wave rectifier has twice the frequency of the input.

Answer 2

1. In the full-wave rectifier, D₁ and D₂ are PN junction diodes that allow current to pass only in forward biasing.
2. During the odd half cycle, the diode D₁ will be forward biased; hence, the potential at Q will be more than the potential at P, and during this cycle, D₂ will not permit current through it.
3. During even half cycles the diode D₂ will be forward biased; hence, the potential at Q will be more than the potential at P, and during this cycle D₁ will not permit current through it.

Hence, we will get DC as output as shown in the diagram.