Question

A Zener diode works on:
A) zero bias
B) reverse bias
C) forward bias
D) infinite bias

Answer 1

Hint : A Zener diode is often used as a voltage regulator since it only allows current to flow in one direction. When a Zener diode allows current to flow in the circuit, the voltage across it remains constant but the current increases drastically.

Complete step by step answer
When a PN junction diode is highly doped with impurities, the higher concentration of ions in the depletion layer causes the width of the depletion layer to become thinner than that in a normally doped PN junction diode. Due to this thinner depletion layer, the voltage drop across the depletion layer is quite high.
If a reverse voltage is applied to the Zener diode and is continued to increase, after a certain applied voltage, the electrons within the depletion region come out and make the depletion region conductive. This is called Zener breakdown. At this point, the voltage across the Zener diode remains nearly constant but the current increases drastically since the path of current is conductive.
While when the Zener diode is connected in forward bias it acts completely similar to a normal PN junction diode but its property of a sharp breakdown voltage in reverse bias is why we use the Zener diode as a voltage regulator since it will only allow current to flow beyond a certain voltage.
So, option (B) is the correct choice.

Note
The voltage point at which the voltage across the Zener diode allows current to flow in reverse bias is called the Zener voltage. For normal Zener diodes, this voltage can range from less than one volt to a few hundred volts. The use of the Zener diode as a voltage regulator is to maintain a constant DC output voltage across the load in the circuit regardless of variations in input current or voltage beyond the Zener voltage.