Question

Draw the circuit diagram of a half-wave rectifier. Explain its working. What is the frequency of ripple in its output?

Answer 1

A device or a circuit which rectifies only one-half of each cycle of an alternating voltage is called a half-wave rectifier.

Electric circuit: The alternating voltage to be rectified is applied across the primary coil (P₁P₂) of a transformer. The secondary coil (S₁S₂) of the transformer is connected in series with the junction diode and a load resistance R_L, as shown in the following figure. The alternating voltage across the secondary coil is the ac input voltage V_i. The de voltage across the load resistance is called the output voltage V₀.

                      Half-wave rectifier circuit

P₁P₂, S₁S₂ - Primary and secondary transformer,

D - Junction diode, 

R_L - Load resistance,

I_L - Load current,

V_i - AC input voltage,

V₀ - DC output voltage

Working: Due to the alternating voltage Vi, the p-region of the diode becomes alternatively positive and negative with respect to the n-region.

During the half-cycle when the p-region is positive, the diode is forward biased and conducts. A current I_L passes through the load resistance R_L in the direction shown.

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

During the next half-cycle, when the p-region is negative, the diode is reverse biased and the forward current drops to zero.

Thus, the diode conducts only during one-half of the input cycle and thus acts as a half-wave rectifier. The intermittent output voltage V₀ has a fixed polarity but changes periodically with time between zero and a maximum value. I_L is unidirectional. The above figure shows the input and output voltage waveforms. The pulsating de output voltage of a half-wave rectifier has the same frequency as the input.