A Zener diode is a silicon semiconductor device that permits current to flow in either a forward or reverse direction. The diode consists of a special, heavily doped p-n junction, designed to conduct in the reverse direction when a certain specified voltage is reached.
A Zener diode is a special type of Diode designed to reliably allow current to flow "backwards" when a certain set reverse voltage, known as the Zener voltage, is reached.
In zener diode there are three node of operation:
Reverse bias with breakdown
In forward bias zener diode act as like P N junction diode . in ideal condition it become short circuit with zero v voltage drop And finite amount of current flowing through it. And in practical case it can be represented with voltage drop and current through it.
Zener diode is a heavily doped diode. It acts as a normal diode in forwarding bias. When the Zener diode is reverse biased the junction potential increases. As the breakdown voltage is high this will provide high voltage handling capacity. In reverse bias it acts like PN junction diode with zero current flowing through it and voltage drop in ideal condition and practical case small amount of current flows called minority current due to reverse bias condition.
The Zener diode is connected parallel with load to make it reverse bias, and once the Zener diode exceeds knee voltage the voltage across the load will become constant. The breakdown voltage of Zener diodes will be constant for a large range of currents. When voltage applied is greater than breakdown voltage then large amount of current flows through it this condition Called as zener diode with reverse biased.
in above fig when load voltage greater than zener break down voltage then load voltage becomes constant and equal to breakdown voltage of diode.
Application of Zener Diode:
Zener diode as voltage regulator.
As a reference element.