Draw the (i) symbol and (ii) the reverse I-V characteristics of a zener diode. Explain briefly, which property of the characteristics enables us to use Zener diode as voltage regulator.

(i) Symbol of Zener diode: 

 

(ii) I-V characteristics: 

 


Zener diode as voltage regulator:

When A.C. input voltage fluctuates in a rectifier, the output also varies. So, we use a zener diode as a voltage regulator to get a constant dc voltage from the unregulated dc output of a rectifier. 

 

For input voltage V_i > V_z (zener voltage), Zener diode is in the breakdown condition. Thus, for wide range of values of load (R_L), current through the Zener diode may change but the voltage across it remains constant. This property of the I-V characteristics enables us to use zener diode as a voltage regulator.