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A little background: I am trying to understand how Zener diodes respond to high voltage transients. I stumbled across discussions of reverse recovery time, and I'm curious how it applies specifically to Zeners.

I understand that Zener diodes aren't typically used in a forward biased mode, which might be the reason manufacturers don't seem to publish the value of reverse recovery time on their data sheets, but I'm still curious about typical values. I found this brief table on Digi-Key, but it doesn't provide any actual values, it only suggests that the reverse recovery time is long compared to Schottky diodes.

JRE
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SteevJobbs
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  • Given people like to throw a zener across almost any signal, to clamp it against severe over-voltages (perhaps with some series resistance), this is quite an appropriate question. – analogsystemsrf Nov 16 '18 at 18:10
  • How longs a piece of string? Every Zener is different so we can't give you a generic awnser. You are limited by whatever data you can find on datasheets and no more unless you test a large batch in the real world. You can find tonnes of Zeners which have various response times on their datasheets. I think you just got to look harder mate. – Curious Diode Nov 16 '18 at 22:18
  • As no one else has mentioned. If you are really that concerned with transients, use a TVS diode and not a Zeners as they are designed to suppress transients where as Zeners are not. – Curious Diode Nov 16 '18 at 22:42

2 Answers2

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If you are using the zener how it is naturally intended i.e. with a reverse voltage applied through a current limiting device such as a resistor, then reverse recovery exits the building because it simply doesn't apply. However, if you are using the zener as a conventional diode i.e. below its zener voltage in reverse and as a normal diode in forward conduction, then reverse recovery does apply when it goes from forward conduction to reverse biased. However, it's unlikely that you'll get many data sheets goinf into detail about it except quite high power devices.

However (and I know it's not the same thing), if you read most data sheets they will tell you about the zener's capacitance and this may cause a significant (but transient) reverse current flow when going from forward conduction to reverse bias and it is akin the reverse recovery in its symptoms.

or is reverse recovery time not applicable to zener diodes?

It is applicable but in 99% of the time, it doesn't play a factor in normal operation and good luck trying to find one with it stated.

Andy aka
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  • Thanks for the response, Andy. In the particular system I'm considering the zener is typically reverse bias, but certain conditions cause it to become momentarily forward biased then rebound quickly to it's reverse biased state. I'm interested in the effect this may have on the diode and if it could potentially cause the diode to fail if there is a large enough reverse recovery current spike. – SteevJobbs Nov 16 '18 at 18:59
  • What is your normal operational current limit device that you must use for a zener in reverse mode. Why can’t this also protect the diode in proper diode mode. – Andy aka Nov 16 '18 at 19:49
  • I have never thought a Zeners capacitance is relivant in transient response as ESR and ESL and never specced? – Curious Diode Nov 16 '18 at 22:21
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I vaguely remember reading about it in a electronics magazine decades ago. Essentially zeners have forward junctions like power rectifiers, not optimized for reverse recovery. Ie in the 2-10 uSec range, depending on zener power rating (say 300 - 3000mA range).

You can easily test your particular device using a buffered scope square wave calibration signal. No prizes here....

abu afeefah
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  • It is application dependent and for this reason a lot of data sheets do not give this value. – Gil Jun 14 '21 at 22:10