Semiconductor Electronics — Part 2: Rectifiers, special diodes and the Zener regulator: visual lesson, ISC Class 12 Physics

Lesson

Rectifiers, Special Diodes and the Zener Regulator

Part 2 — from alternating mains to a steady supply, light-emitting and light-sensing diodes, and a diode that holds a voltage.

In this lesson you will

Draw and explain the half-wave and centre-tap full-wave rectifiers, their waveforms, the role of each component and the filter capacitor
Explain how an LED, a photodiode and a solar cell work and why LEDs save energy
Explain the Zener diode characteristic and the voltage regulator, and solve simple numericals on the series resistor and load current

Diagram

The half-wave rectifier

A transformer steps the 230 V mains down; its secondary is connected in series with a diode D and the load R_L.

Positive half-cycle: D is forward biased, so a current flows through R_L.
Negative half-cycle: D is reverse biased, so there is no current.
The output is a train of positive pulses, one for each input cycle: the same frequency as the input (50 Hz), with a large ripple.

Diagram

The centre-tap full-wave rectifier

The secondary has a centre tap C. The ends A and B are at equal and opposite voltages with respect to C and go to the anodes of D₁ and D₂; the cathodes are joined to the load, whose other end goes to C.

When A is positive, D₁ conducts; when B is positive, D₂ conducts.
The current always flows the same way through R_L: two pulses per input cycle.
Ripple frequency = 2 × 50 = 100 Hz.

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