Question

For the zener diode shown in the figure, the zener voltage at knee is 7V, the knee current is negligible and the zener dynamic resistance is 10Ω. If the input voltage (Vi) ranges from 10 to 16 volts, the output voltage (Vo) ranges from?

(a) 7 to 7.29V

(b) 6 to 7V

(c) 7.14 to 7.43V

(d) 7.2 to 8V

I got this question in an online interview.

My question comes from Breakdown Diodes in section Semiconductor-Diode Characteristics of Electronic Devices & Circuits

Answer 1

Right answer is (c) 7.14 to 7.43V

To explain I would say: If i is the current flowing, then V0=10i+7

i=(VI-7)/210. By substituting, if VI=10V then i=1/70 and V0=(1/7)+7=7.14V

if VI =16V then i=3/70 and V0=(3/7)+7=7.43V.