Explain the construction and working of a full wave rectifier.

Explanation

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 centre is usually taken as the ground or zero voltage reference point. Due to the centre tap transformer, the output voltage rectified by each diode is only one half of the total secondary voltage.
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 biased diode `D_1` and reverse biases diode `D_2`. Hence, being forward biased, diode `D_1` conducts and current flows along the path `MD_1AGC.` As a result, 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 biased diode `D_2` and reverse biases diode `D_1`. Hence, being forward biased, diode `D_2` conducts and current flows along the path `ND_2BGC`. As a result, 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 figure (b). Though both positive and negative half cycles of ac input are rectified, the output is still pulsating in nature.
The efficiency (`eta`) of 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.