Question

A zener diode having zener voltage $8\text{V}$ and power dissipation rating of $0.5\text{W}$ is connected across a potential divider arranged with maximum potential drop across zener diode is as shown in the diagram. The value of protective resistance $R_p$ is ______$\Omega$.

Answer 1

Given:
$P=0.5\text{W};V=8\text{V}$

Power, $P=Vi$

$0.5=8i\Rightarrow i=\frac{1}{16}\text{A}$

So, voltage across protective resistance $R_p$ will be,

$V_R=20-8=12\text{V}$

$\therefore R_p=\frac{V_R}{i}=12\times 16=192\Omega$

So, correct answer $:192\Omega$