What is Zener diode? Working and its application.

  What is Zener diode?

Zener diode is a special type of p-n junction semiconductor diode which allows the current to flow both in the forward and the reverse direction. It is a form of semiconductor diode in which at a critical reverse voltage a large reverse current can flow.

Zener diode is also known as breakdown diode because a heavily doped semiconductor diode which is formed to operate in reverse direction.

Symbol of zener diode

The name Zener diode was named after the American physicist Clarence Melvin Zener who discovered the zener effect. It can work in forward bias as that of p-n junction diode and it can also work in reverse bias that makes it special. In reverse bias zener diode works as a voltage regulator.   

It is given name "Zener diode " after its inventor C.Zener. In zener diode the N & P regions are heavily doped. As a result of it, then depletion region of Zener diode is extremely thin ( 1/1000000 metre ) and the electric field set up across the junction is very high.

 Equivalent circuit of zener diode 

1: ON state : 

If we establish a circuit and apply a voltage to the zener diode, positive terminal of voltage is connected with cathode side of zener diode and negative terminal of voltage is connected with anode side of zener diode but the condition is voltage supply (V) is greater than the Vz as shown in the figure given below.

                                                       

                                                  

2: OFF state: 

 If we establish a circuit and apply a voltage to the zener diode, positive terminal of voltage is connected with cathode side of zener diode and negative terminal of voltage is connected with anode side of zener diode but the condition is voltage supply (V) is less than the Vz as shown in the figure given below. 

                                                                 

Some special features of zener diode :

1: It is very highly doppe.

2: Sharp breakdown voltage.

3: Low reverse breakdown voltage.

4: It conducts in reverse direction also.

5: It can also operate after breakdown.

6: Narrow depletion layer.

7: It is faster than the the normal diode when used as switch.

8: Greater power rating.  

Characteristics of Zener diode:

The Zener diode  is  normally operated in reverse breakdown and the current direction is then from anode to cathode.

The figure shows, the forward characteristics is same as that of ordinary forward biased junction diode.

                         

                          

In reverse biased heavily doped Si ( or Ge ) p-n junction diode operated in breakdown region, due to high temperature tolerance of silicon material so it is preferred as compared to Ge. As the reverse voltage applied to p-n junction is increased greatly from its normal cut off value, hence this voltage is called Zener voltage, Vz or breakdown voltage. When the voltage reaches the breakdown voltage, suddenly current flow through it. If we increases the reverse voltage the leakage current remains essentially constant until the breakdown voltage is reached where the current increases. 

Application of Zener diode :  

1: It is widely used as voltage regulator or shunt regulator.

2: It used as switch because Zener diode can produce a drastic change from lower current to high current.

3: Used in overcurrent and overvoltage protection circuits.

4: These are also used in operational amplifier as clipper or clamper.