Question: Q. 4. A zener diode is fabricated by heavily doping both $p$ and $n$ sides of the junction. Explain, why? Briefly explain the use of zener diode as a $d c$ voltage regulator with the help of a circuit diagram.
U] [Delhi II 2017]
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Solution:
Ans. Explanation of heavily doping of both $p$ and $n$ sides of Zener diode.
Circuit diagram of Zener diode as a dc voltage regulator.
1
Explanation of the use of Zener diode as a $d c$ voltage regulator.
By heavily doping both $p$ and $n$ sides of the junction, depletion region formed is very thin, i.e., $<10^{-6} \mathrm{~m}$. Hence, electric field, across the junction is very high $\left(5 \times 10^{6} \mathrm{~V} / \mathrm{M}\right)$ even for a small reverse bias voltage. This can lead to a ‘breakdown’ during reverse biasing.
If the input voltage increases/decreases, current through resister $R_{s}$, and Zener diode, also increases/decreases. This increases/decreases the voltage drop across $R_{s}$ without any change in voltage across the Zener diode.
This is because, in the breakbown region, Zener voltage remains constant even though the current through the Zener diode changes.
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