Question

Explain the construction and working of a full-wave rectifier.

Answer 1

Full-wave rectifier: The positive and negative half cycles of the AC input signal pass through the full-wave rectifier circuit and hence it is called the full-wave rectifier. It consists of two p-n junction diodes, a center-tapped transformer, and a load resistor (R_L). The center is usually taken as the ground or zero voltage reference point. Due to the center tap transformer, the output voltage rectified by each diode is only one-half of the total secondary voltage.

                Full-wave rectifier circuit

                Input and output waveforms

During positive half cycle:
When the positive half cycle of the ac input signal passes through the circuit, terminal M is positive, G is at zero potential and N is at negative potential. This forward biases diode D₁ and reverse biases diode D₂. Hence, being forward biased, diode D₁ conducts and current flows along the path MD₁ AGC. As a result, the positive half cycle of the voltage appears across R_L in the direction G to C.

During negative half cycle:
When the negative half cycle of the ac input signal passes through the circuit, terminal N is positive, G is at zero potential and M is at negative potential. This forward biases diode D₂ and reverse biases diode D₁. Hence, being forward biased, diode D₂ conducts and current flows along the path ND₂ BGC. As a result, the negative half cycle of the voltage appears across R_L in the same direction from G to C.

Hence in a full-wave rectifier both positive and negative half cycles of the input signal pass through the circuit in the same direction as shown in the figure. Though both positive and negative half cycles of ac input are rectified, the output is still pulsating in nature. The efficiency (η) of a full-wave rectifier is twice that of a half-wave rectifier and is found to be 81.2%. It is because both the positive and negative half cycles of the ac input source are rectified.