can anybody say what happens when the zenerdiode is connected in reverse bias with AC SUPPLY

 

The Zenerdiode start to conduct after it reaches zener breakdown voltage.

Eg:
If u apply 10V AC to the zener of 5.1V value, it start 2 conduct when I/P voltage is increased beyond 5.1V. The load follow the I/P.

 

A zener acts much like a regular diode, until the breakdown voltage is reached. You would get something that vaugly resembles a square wave.

 

i think zener diode behaves normally under forward voltage n breaksdown at its breakdownlimit ...n then constant current starts flowing through it......under reverse bias it will not damaged .....current
flow after it s breakdown....

 

No. It is not constant current. It is a relatively constant voltage, which is why zener diodes are used for voltage references. Once it is back biased to it's breakdown voltage (zener voltage) it conducts just enough to keep the same voltage across it, reguardless of current. You can burn them out by having too much current flowing through them, as they dissapate power like a resistor (P(watts) = V (zener voltage) * Current). All zener diodes have a wattage rating for this reason.

 

Their voltage in either direction is not constant either (but varies much much less than the current so it is called constant).

under reverse bias it will not damaged

This is true for "regular" didoes also -- what damages them is if you exceed their rated power.

 

Hello,

Zener diodes can be used for several aplication.
http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/zener.html
As a limiter for AC :
http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/limiter.html
Or as a regulator for DC :
http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/zenereg.html

Greetings,
Bertus

 

You may also find the information on zener diodes contained in the AAC ebook helpful.

hgmjr