Re: Low voltage zener diodes

On 9/10/2024 2:50 am, john larkin wrote:

On Tue, 8 Oct 2024 12:08:20 +0200, Gerhard Hoffmann <dk4xp@arcor.de>
wrote:
 

Am 08.10.24 um 11:24 schrieb Pimpom:

When I tested some low voltage zener diodes (<<5V) 30-40 years ago, I
found that they didn't have even a reasonably sharp knee, behaving more
like LEDs in forward mode, maybe worse. Do I remember correctly? Are
they still the same?

>
yes, that's true. At > 5V they are really avalanche diodes. Around 5-7V
it is a mix. Zeners & avalanche diodes have a different TC, and it
compensates at around 6V.
>
You can see the onset of avalanche behavior in the noise spectrum with
rising voltage. True Zeners are much better here. For the BZX84 family:
>
<
https://www.flickr.com/photos/137684711@N07/24411798996/in/album-72157662535945536
   >
>
Prof. Zener even sued the industry not to use his name for avalanche
thingies because it was not "his" effect. They settled on Z-Diodes
pretending it was for the V/I curve. But in the end the ghost was out of
the bottle.
>
Gerhard
>
>
>

 Everybody calls them all zeners now.
 You can actually get a zener to oscillate.
 https://www.dropbox.com/scl/fi/uvbj2tmrlitfv233ncamr/Zener_Noise.pdf?rlkey=bqxynlx8g1r6b6cfiimfaejuo&raw=1
 Expensive noise diodes are probably just selected zeners.

We had a long thread about that here many years ago. The concensus was that they didn't actually oscillate - an avalanche zener run a very low current had a finite chance of self-extinguishing the avalanche and turning it back on again when the next cosmic ray went past, which is what your pencil sketch seems to show.
--
Bill Sloman, Sydney