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Thursday, 12 July 2012

Zener diode

Zener diode
It is a heavily doped PN junction made of Germanium or Silicon and works
At the breakdown region  in reverse bias condition zener diodes are commonly made of Si instead of Ge because Si has the ability to bear more current and temperature. It is just like the common diode , only the two ends of the line that shows cathode are bended .As shown as figure.

Working Principle & V/I characteristics:
When the zener diode is forward biased , then the resistance o-f the circuit is low. And this works as a common silicon diode at a voltage of 0.7 v (0.3 v for Ge). Its Forward Current starts to increase rapidly. As shown in the curve given below.

When it is reverse biased then  the resistance of circuit is very high . and a low value of reverse current flows through it ( Leakage Current ).
When its reverse voltages are further increased then at a certain point the junction is break down and reverse current increases rapidly , whose value is limited by applying an external resistance in series o-f junction .
A critical value of voltage at which this condition occurs is known as breakdown voltage.
If the voltage is further increased  then the current increases rapidly while the voltages in the breakdown region , almost stable as shown in the curve.
Zener Biasing:
For the proper function of a zener diode , its biasing must be proper .thus , during the biasing of zener diode , following points should be taken care of :-
  1. Zener diode must be always reverse biased .
  2. Its parallel reverse voltages must be always higher than (Vz).
  3. its should be installed in a circuits in which current flows less than ( Iz max).



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