Role of Zener Impedance in Zener Diode Selection

Thread Starter

mishra87

Joined Jan 17, 2016
1,034
Hello All,

I have to select Zener Diode, so what is role of Zener impedance.
A higher or lower impedance would be better and why ???

What all parameters need to be taken care Zener diode selection.

Thanks in Advance !!!
 

wayneh

Joined Sep 9, 2010
17,493
Hello All,

I have to select Zener Diode, so what is role of Zener impedance.
The impedance is essentially the DC resistance, and it will cause ohmic heating of the zener when current is flowing.
A higher or lower impedance would be better and why ???
Lower is better but will track with cost.
What all parameters need to be taken care Zener diode selection.
The two big ones are the breakdown voltage and the current rating. Other parameters (like package size, lead spacing, temperature ratings, etc.) might be important depending on your application.
 

crutschow

Joined Mar 14, 2008
33,962
The dynamic impedance of a Zener causes a change in the Zener voltage with current (when above the breakdown voltage).
It's thus determines the accuracy of the voltage with change in current.
If the Zener current doesn't change in operation, than the Zener impedance is not critical.

If you want a low Zener impedance with an accurate voltage, then you might consider a programmable reference, such as a TL431, which can simulate an accurate Zener with a programmable breakdown voltage.
If you need a higher power capability, it can be boosted with an added power transistor (shown in its data sheet).
 

crutschow

Joined Mar 14, 2008
33,962
The impedance is essentially the DC resistance, and it will cause ohmic heating of the zener when current is flowing.
I'm not certain this is true but it made sense as I wrote it!
It's true, but the dissipation from that is typically much less than the dissipation from the Zener breakdown voltage, so it's usually not a concern from a dissipation point-of-view.
 
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