# (a) Write the principle of a semiconductor device which is used as a voltage regulator.(b) With the help of a circuit diagram explain its working.(c) Draw its I -V characteristics.

(a) Zener diode is the semiconductor device which is used as a voltage regulator.

In the case of reverse-biased Zener diode as the reverse voltage increases current also increases. But at a particular reverse voltage condition reverse breakdown occurs, at that time current increases sharply and the voltage across Zener diode remains constant. That voltage is known as Zener voltage $(V_{z})$. This is the principle applied when Zener diode is used as a voltage regulator.

(b)

Here $V_{i}-V_{o}= IR$

$\frac{V_{i}-V_{o}}{I}= R$

By Kirchoff's law, $I = I_{z}+I_{l}$

In this case when input voltage increases the current through R and Zener diode increases. This results in the voltage drop across R increases but the voltage across the Zener diode is constant. This is because reverse breakdown condition Zener voltage remains constant even if the current through Zener diode increase. Similarly, if the input voltage decreases current through R and Zener diode decreases. This results voltage drop across R decreases but the voltage drop across Zener diode is constant. Thus, it can act as a voltage regulator.

(c)

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