JEE Main 2023 · 1 February · evening · Single correct · +4 / −1
Choose the correct statement about Zener diode :
- (a) It works as a voltage regulator in reverse bias and behaves like simple pn junction diode in forward bias.
- (b) It works as a voltage regulator in both forward and reverse bias.
- (c) It works as a voltage regulator only in forward bias.
- (d) It works as a voltage regulator in forward bias and behaves like simple pn junction diode in reverse bias.
Answer and solution
Answer (a) It works as a voltage regulator in reverse bias and behaves like simple pn…
Solution
Physics sir · 4 steps
A Zener earns its living at breakdown, and breakdown only happens in reverse bias.
- Forward bias. A Zener diode is still a pn junction. In forward bias it switches on at about 0.7 V for silicon and conducts like any ordinary diode, so nothing special happens there.
- Reverse bias. Its p and n sides are very heavily doped, so the depletion layer is very thin. At a sharp reverse voltage V_Z the junction breaks down, and the current can then change over a wide range while the voltage across the diode stays almost fixed at V_Z.
- Why it regulates. A voltage regulator must hold the output voltage steady even when the input or the load changes. The Zener does exactly this in reverse breakdown, with a series resistor taking up the extra voltage.
- So. It regulates in reverse bias and behaves like a normal pn junction diode in forward bias. The answer is (a).
The idea to keep. Zener in reverse breakdown holds a constant V_Z whatever the current, and that is regulation. In forward bias it is just an ordinary diode.
Answer from the NTA final answer key. Solution by PrepWiser.