Question

Assume that the supply voltage in the figure shown below starts decreasing from 30 V to 0. 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

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