Question
Name the semiconductor device that can be used to regulate an unregulated dc power supply. With the help of I-V characteristics of this device, explain its working principle.
Solution
Zener diode can be used to regulate an unregulated dc power supply. 
Working principle of Zener diode as per the V-I characteristics:
In reverse breakdown region or zener region, a very small change in voltage across the zener diode produces very large change in current through the circuit but the voltage across the zener remains constant.
