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  4. In a circuit, zener diode of zener voltage 12 V works with a load resistance RL=1 k Ω and series resistance Rs=100 Ω. If current through zener diode is 18 mA, then find the applied external voltage (in volt).

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Q. In a circuit, zener diode of zener voltage $12\, V$ works with a load resistance $R_{L}=1 \,k \,\Omega$ and series resistance $R_{s}=100 \Omega$. If current through zener diode is $18 \,mA$, then find the applied external voltage (in volt).

Semiconductor Electronics: Materials Devices and Simple Circuits

Solution:

According to the question,
$I_{Z}=18 \,mA$
$I_{L}=\frac{12}{1 \times 10^{3}}$
$ \Rightarrow 12 \, mA$
$I=I_{Z}+I_{L}=30 \, mA$
Voltage drop on $R_{s}$ is
$V_{s}=I R_{s}=100 \times 30 \times 10^{-3}=3\, V$
External voltage $=12 \,V +3\, V =15\, V$