Question

In the circuit below, the knee current of ideal zener diode is 10mA. To maintain 5V across the RL, the minimum value of RL is?

(a) 120

(b) 125

(c) 250

(d) 100

This question was addressed to me in a job interview.

Question is from Breakdown Diodes topic in section Semiconductor-Diode Characteristics of Electronic Devices & Circuits

Answer 1

Correct choice is (b) 125

To explain: Here, IKNEE=10mA, VZ=5V. I=IL+IZ. I= (10-5)/100=50mA

Now, 50=10+ILMAX .

ILMAX=40mA. RLMIN=5/40mA=125 Ω.