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

Two diodes, fed from a centre-tapped secondary, conduct on alternate half-cycles so that both halves of the AC input get converted into unidirectional current pulses through the load.

Circuit (centre-tap full wave rectifier), described: The secondary winding of a transformer is centre-tapped, with the centre tap grounded/connected to one end of the load resistor $R_L$. The two outer ends of the secondary are connected to the anodes of two diodes $D_1$ (top) and $D_2$ (bottom); the cathodes of both diodes are joined together and connected to the other end of $R_L$.

Working:

• During the positive half-cycle of the AC input, the top end of the secondary is positive with respect to the centre tap. This forward-biases $D_1$ (which conducts) while reverse-biasing $D_2$ (which is cut off). Current flows through $D_1 \to R_L \to$ centre tap, in a fixed direction through $R_L$.
• During the negative half-cycle, the bottom end of the secondary is now positive with respect to the centre tap. This forward-biases $D_2$ (conducts) while $D_1$ is reverse-biased (cut off). Current again flows through $R_L$ in the same direction as before (via $D_2 \to R_L \to$ centre tap).
• Since current flows through the load in the same direction during both halves of the input cycle, the rectifier is called a full wave rectifier.

Waveforms: …