Modern Physics Ques 216
- Figure shows a DC voltage regulator circuit, with a Zener diode of breakdown voltage $=6 $ $ V$. If the unregulated input voltage varies between $10 $ $V$ to $16 $ $V$, then what is the maximum Zener current?
(Main 2019, 12 April II)
(a) $2.5$ $ mA$
(b) $1.5$ $ mA$
(c) $7.5$ $ mA$
(d) $3.5$ $ mA$
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Answer:
Correct Answer: 216.(d)
Solution:
- In given voltage regulator circuit breakdown of Zener occurs at $6 $ $V$.
After breakdown, voltage across load resistance $\left(R _L=4 k \Omega\right)$ is,
$ V=V _Z=6 $ $V $
$\therefore$ Load current after breakdown,
$ I _L=\frac{V _Z}{R _L}=\frac{6}{4000}=1.5 \times 10^{-3} $ $A $
When unregulated supply is of $16 $ $V$, potential drop occurring across series resistance $\left(R _S=2 k \Omega\right)$ is;
$ V _S=V-V _Z=16-6=10 $ $V $
So, current across series resistance is
$ I _S=\frac{V _S}{R _S}=\frac{10}{2 \times 10^{3}}=5 \times 10^{-3} $ $A $
So, current across Zener diode is
$ I _Z=I _S-I _L=5 \times 10^{-3}-1.5 \times 10^{-3}=3.5 \times 10^{-3} $ $A $
BETA
