Zener Diode

Circuit symbol of zener diode

Operating principle and characteristics of zener diode will be explained in this section:-
When reverse biasing across a p-n junction diode(For more information on p-n junction please refer to  http://dutta60.blogspot.in/2014/07/p-n-junction-diode.html) is increased beyond the breakdown voltage as a consequence of which reverse current increases rapidly, then the diode is said to oprate in reverse breakdown region and is termed as zener diode.Now the question is how the breakdown is achieved-When the p-n junction is reverse biased free electrons get energised and is accelerated by the reverse electric field .These electrons then collide with atoms and ionise them as a result of which more electrons are generated resulting in more atoms being ionised.As the no. of electrons generated is more reverse current increases abruptly.When the p-n junction is highly reverse biased electric field across the junction is very high and the zener breakdown occurs.After reading this one more question may arise that how the electrons are generated-what happens is that the electric field exerts a force on electrons of the outermost shells of the atoms and pulls it away thereby ionising it instantly.On the other hand the reverse current keeps on increasing due to this.

CHARACTERISTICS:-

Here I am only going to discuss about the negative portion of the graph as that is the operating region of zener diode.As you can see from the graph itself that at a particular voltage or reverse voltage you can say the curve falls almost linearly .The breakdown point at which this occurs is termed as the knee of the curve and the breakdown process starts at this point.As you can see below the breakdown point reverse current is almost negligible but when the voltage is more than the breakdown voltage zener breakdown occurs and current increases almost linearly after that.However the zener diode operates between specified range of current values .This range of current must be maintained for the operation of zener diode in the breakdown region.

That's all for now!!Happy reading!!