Question

Figure shows a $\text{DC}$ voltage regulator circuit, with a Zener diode of breakdown voltage $=6\text{V}.$ If the unregulated input voltage varies between $10\text{V}$ to $16\text{V},$ then what is the maximum Zener current ?

• A. $7.5\text{mA}$
• B. $2.5\text{mA}$
• C. $3.5\text{mA}$
• D. $1.5\text{mA}$

Answer 1

The correct option is C $3.5\text{mA}$

Given, $V_Z=V_L=6\text{V}$

The maximum Zener current will be corresponding to maximum unregulated voltage $\left(16\text{V}\right)$. So,

$I_L=\frac{V_L}{R_L}=\frac{6}{4\times {10}^3}$

$\therefore I_L=1.5\times {10}^{-3}\text{A}=1.5\text{mA}$

And, $I_S=\frac{16-V_L}{2\times {10}^3}$

$=\frac{(16-6)}{2}\times {10}^{-3}=5\text{mA}$

Now, applying $\text{KCL}$,

$I_S=I_Z+I_L$

$\Rightarrow 5=I_Z+1.5$

$\Rightarrow I_Z=3.5\text{mA}$

Hence, $\left(\text{B}\right)$ is the correct answer.