Question

Which of the following statement is false for a zener diode voltage rated as “VZ“?

(a) Reverse breakdown occurs at VZ

(b) Forward breakdown occurs at VZ

(c) Zener diode is a heavily doped diode

(d) Usually operates in reverse bias mode

This question was posed to me in an interview for internship.

This intriguing question comes from Voltage-Ampere Characteristics of Diode in portion Diode Circuit of Analog Circuits

Answer 1

The correct option is (b) Forward breakdown occurs at VZ

To explain I would say: Voltage rating is the voltage at which reverse breakdown occurs. Voltage rating of a zener diode indicates the voltage beyond which current increases rapidly. Beyond this point increase in reverse bias voltage will only reflect on current which means voltage drop beyond this point is almost constant. This phenomenon holds the key role in the working of zener diode as a voltage regulator. Zener diode is a heavily doped diode because for zener breakdown we need a narrow junction. It operates in reverse bias mode. In forward bias mode it operates as a normal diode.