Question

With the help of a circuit diagram, explain the working of a full wave rectifier. Depict the input and output waveforms.

Hint:

Ripple frequency of full-wave rectifier is $2f$ (where $f$ is supply frequency, e.g., $100\text{ Hz}$ for $50\text{ Hz}$ input), whereas for half-wave rectifier it is $f$. Peak inverse voltage across non-conducting diode is $2V_m$.

Answer 1

Concept:
• A full-wave rectifier converts both positive and negative half-cycles of an alternating input voltage into unidirectional direct current (DC).

• It utilizes a center-tapped transformer and two p-n junction diodes operating in alternate conduction modes during opposite half-cycles.

Step 1: Circuit Diagram Construction
The circuit consists of a center-tapped secondary winding of a transformer, two p-n junction diodes ($D_1$ and $D_2$), and a load resistor $R_L$ connected between the junction of the diodes' cathodes and the central tap of the transformer secondary.

Step 2: Working During Positive Half-Cycle
During the positive half-cycle of input AC voltage:
Terminal $A$ of the secondary winding becomes positive with respect to the center-tap $C$, while terminal $B$ becomes negative.
Diode $D_1$ becomes forward-biased and conducts current.
Diode $D_2$ becomes reverse-biased and remains non-conducting.
Current flows through load resistor $R_L$ in the direction from $X$ to $Y$.

Step 3: Working During Negative Half-Cycle
During the negative half-cycle of input AC voltage:
Terminal $A$ becomes negative with respect to center-tap $C$, while terminal $B$ becomes positive.
Diode $D_1$ becomes reverse-biased and ceases conduction.
Diode $D_2$ becomes forward-biased and conducts current.
Current again flows through load resistor $R_L$ in the exact same direction from $X$ to $Y$.

Step 4: Input and Output Waveforms
Since current flows through load $R_L$ in the same direction during both half-cycles, a continuous pulsating DC voltage is obtained across $R_L$.

Step 5: Conclusion
A full-wave rectifier conducts during both half-cycles of input AC, producing a pulsating DC output with twice the frequency of the input AC supply ($f_{out} = 2 f_{in}$).