Question

For the circuit shown below, the current through the Zener diode is

• A. $9\text{mA}$
• B. $5\text{mA}$
• C. Zero
• D. $14\text{mA}$

Answer 1

The correct option is A $9\text{mA}$

Assuming zener diode doesnot break down,
current in circuit is$\frac{120}{15000}\text{A}=8\text{mA}$
Potential across $R_2$ is $80\text{V}>$ breakdown voltage.
Hence Zener diode breaks down.

The voltage across zener diode is constant


$i_{1\left(R_2\right)}=\frac{V}{R}=\frac{50}{10\times {10}^3}=5\times {10}^{-3}\text{A}$
$i_{\left(R_1\right)}=\frac{V}{R}=\frac{120-50}{5\times {10}^3}=14\times {10}^{-3}\text{A}$

$\therefore i_{zenerdiode}=14\times {10}^{-3}-5\times {10}^{-3}=9\times {10}^{-3}=9\text{mA}$.