Question

In a circuit the load current is 5 mA and the unregulated output is 10 V. If the voltage drop across the Zener diode is 3 V, what should be the value of resistance?

(a) 50 Ω

(b) 100 Ω

(c) 125 Ω

(d) 150 Ω

This question was addressed to me in an online interview.

Origin of the question is Zenner Diode in division Semiconductors of Engineering Physics II

Answer 1

Right choice is (d) 150 Ω

The explanation: The value of R should be such that the current through the Zener diode is much larger than the load current.

Imagine, Iz = 20 mA. The total current is therefore 24 mA.

The voltage drop = 3 V

Resistance = 3 V/24 X 10^-3 A

Resistance = 125 Ω.