Zener diode

  • #1
Why doesn't the voltage vary beyond breakdown voltage in zener diode?
 

Answers and Replies

  • #2
LvW
820
220
In fact, it does vary. The finite slope of the Iz-Vz characteristic is expressed in form of a dynamic (differential) resistance rz which assumes rather small values (some ohms).
More than that, this value (the slope) is not constant but varies with the current Iz.
 
Last edited:
  • #3
743
142
It does.

There is a voltage-current curve, it just has a sharp knee.

The reason the knee is so sharp is because the Zener effect is based on tunneling.
 
  • #4
meBigGuy
Gold Member
2,323
405
To answer your basic question, from https://en.wikipedia.org/wiki/Zener_effect

"Under a high reverse-bias voltage, the p-n junction's depletion region expands, leading to a high strength electric field across the junction. A sufficiently strong electric field enables tunneling of electrons from the valence to the conduction band of a semiconductor leading to a large number of free charge carriers. This sudden generation of carriers rapidly increases the reverse current and gives rise to the high slope conductance of the Zener diode."

So, a reverse biased diode has a non-destructive breakdown voltage, above which it has significant conductance compared to below it.
 
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