Question

Assume that the supply voltage in the figure shown below starts decreasing from 30 V to 0 V. The maximum supply voltage at which the zener diode loses its regulating ability is ___V.

• A. 27

Answer 1

The correct option is A 27
The drop across zener diode must be 12 V.

$\therefore V_s\times \frac{R_L}{R_L+R_s}=12$

$V_s=12\times (1+\frac{R_s}{R_L})$

$=12\times (1+\frac{100}{80})=27V$