Question

Draw the circuit diagram of a half wave rectifier and explain its working.

Answer 1

The half-wave rectifier circuit. The circuit consists of a transformer, a p-n junction diode and a resistor. In a half-wave rectifier circuit, either a positive half or the negative half of the AC input is passed through while the other half is blocked. Only one-half of the input wave reaches the output. Therefore, it is called a half-wave rectifier. Here, a p-n junction diode acts as a rectifying diode.

                       Half-wave rectifier circuit

           Input and output waveforms

During the positive half cycle:
When the positive half cycle of the ac input signal passes through the circuit, terminal A becomes positive with respect to terminal B. The diode is forward biased and hence it conducts. The current flows through the load resistor R_L and the AC voltage developed across R_L constitutes the output voltage V₀ and the waveform of the diode current.

During the negative half cycle:
When the negative half cycle of the ac input signal passes through the circuit, terminal A is negative with respect to terminal B. Now the diode is reverse biased and does not conduct and hence no current passes through R_L. The reverse saturation current in a diode is negligible. Since there is no voltage drop across R_L, the negative half cycle of ac supply is suppressed at the output.

The output of the half-wave rectifier is not a steady dc voltage but a pulsating wave. This pulsating voltage is not sufficient for electronic equipment. A constant or a steady voltage is required which can be obtained with the help of filter circuits and voltage regulator circuits. Efficiency (η) is the ratio of the output dc power to the ac input power supplied to the circuit. Its value for a half-wave rectifier is 40.6 %.