The following figure shows the V-I characteristics of a semiconductor diode
(i) Identify the semiconductor diode used.
(ii) Draw the circuit diagram to obtain the given characteristic of this device.
iii) How the characteristic of zener diode can be used as a voltage regulator?
(i) The semiconductor diode whose V-I characteristic is shown in the figure is Zener diode.
(ii) Circuit diagram to obtain the given characteristic is shown in Fig. 
(iii) The circuit of Zener diode used as voltage regulator is shown in Fig. 
The voltage to be regulated is applied across Zener diode. When input voltage increases, the current in Zener diode circuit also increases. As a result, voltage drop across series resistance Rs increases but, voltage drop across RL remain same. That is, the voltage drop across Zener diode remains the same.
Similarly, when voltage decreases, current in the zener diode circuit decreases and voltage drop across series Rs resistance decreases but, across the load resistance remains the same. This is how, voltage is regulated using a zener diode.
