With the help of a neat circuit diagram, explain the working of a half wave rectifier. Draw input and output waveforms.

Answer:

Circuit: [Figure: AC mains connected to the primary P₁P₂ of a transformer; one end S₁ of the secondary is connected to the p-side (anode) of a junction diode D; the n-side (cathode) is connected through a load resistance \(R_L\) to the other end S₂ of the secondary. Output is taken across \(R_L\).]

Working:

• Positive half cycle: end S₁ is positive with respect to S₂. The diode is forward biased, it conducts, and current flows through \(R_L\) in one direction. An output voltage appears across \(R_L\).
• Negative half cycle: S₁ is negative with respect to S₂. The diode is reverse biased and does not conduct (only negligible reverse current). No current flows through \(R_L\), so the output is zero.

Thus current flows through the load only during alternate half cycles and always in the same direction. The output is unidirectional but pulsating DC. Only half the input wave is used, so the efficiency is low (maximum about 40.6%).

Waveforms: [Figure: (a) input voltage versus time: a sine wave with positive and negative half cycles; (b) output voltage across \(R_L\) versus time: only the positive half cycles (humps), with zero output during the negative half cycles.]