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Zeners in Series

Started by Cursitor Doom November 9, 2019
Whilst mere hobbyists like myself can easily get away with making up a 
desired zener value from putting two smaller value ones in series to add 
together their rated voltages, can such a dodge be employed by 
professional designers without losing face? I mean, in the case where 
there is no commercially available zener with precisely the desired 
breakdown voltage? Would a pro designer be open to ridicule and risking 
his rep by pulling such a stunt?



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Cursitor Doom wrote:

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> > Whilst mere hobbyists like myself can easily get away with making up a > desired zener value from putting two smaller value ones in series to add > together their rated voltages, can such a dodge be employed by > professional designers without losing face? >
** Yep, engineering = making what you need with what you have got.
> I mean, in the case where > there is no commercially available zener with precisely the desired > breakdown voltage? Would a pro designer be open to ridicule and risking > his rep by pulling such a stunt? >
** I have used series strings of 8 or more 12V 3W zeners to get high voltage and high power dissipation - all mounted on a tag strip. Fitting them in series with the screens supply of output tubes to stop overheating damage when clipping. 100V, 20W zeners need an isolated heatsink and are not cheap. You do what you need to do. Only wankers worry about how it looks. .... Phil
On 09/11/19 21:42, Cursitor Doom wrote:
> Whilst mere hobbyists like myself can easily get away with making up a > desired zener value from putting two smaller value ones in series to add > together their rated voltages, can such a dodge be employed by > professional designers without losing face? I mean, in the case where > there is no commercially available zener with precisely the desired > breakdown voltage? Would a pro designer be open to ridicule and risking > his rep by pulling such a stunt?
My question would be "what is the problem to which you think that is a good solution?". Only then I would consider whether that is an adequate thing to do. If nothing else, you should assure yourself that the voltage will be sufficiently accurate and stable as temperature and current vary.
Cursitor Doom wrote:
> Whilst mere hobbyists like myself can easily get away with making up a > desired zener value from putting two smaller value ones in series to add > together their rated voltages, can such a dodge be employed by > professional designers without losing face? I mean, in the case where > there is no commercially available zener with precisely the desired > breakdown voltage? Would a pro designer be open to ridicule and risking > his rep by pulling such a stunt? > > >
Oil 4 Less® LLC makes their low noise Codatron® high voltage zener, capable of operation to 204 degrees Centigrade / 400 degrees Fahrenheit and can program them from 50V to 2500V in 50V steps. A ten volt step version is in prototype now. Been sold for over ten years, and in many countries. What voltage and quantities are you looking for?
Transorbs are two way senders and we employ two in series based upon power considerations
On Saturday, November 9, 2019 at 4:42:43 PM UTC-5, Cursitor Doom wrote:
> Whilst mere hobbyists like myself can easily get away with making up a > desired zener value from putting two smaller value ones in series to add > together their rated voltages, can such a dodge be employed by > professional designers without losing face? I mean, in the case where > there is no commercially available zener with precisely the desired > breakdown voltage? Would a pro designer be open to ridicule and risking > his rep by pulling such a stunt? > > > > -- > This message may be freely reproduced without limit or charge only via > the Usenet protocol. Reproduction in whole or part through other > protocols, whether for profit or not, is conditional upon a charge of > GBP10.00 per reproduction. Publication in this manner via non-Usenet > protocols constitutes acceptance of this condition.
But, is it really good practice to use only a stack of zeners? Should there not be a hi impedance bleeder path in parallel to each of the diode(s) stack so they all start to conduct and zener properly. Phil I'm surprised you did not mention this.
 alan.ye...@gmail.com wrote:
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> > > But, is it really good practice to use only a stack of zeners? > Should there not be a hi impedance bleeder path in parallel to > each of the diode(s) stack so they all start to conduct and zener > properly. > Phil I'm surprised you did not mention this.
** Surely you jest ? Might as well fit bleeders in parallel with cells in a battery. Make the bastards share the damn current .... ... Phil
Cursitor Doom wrote:
> Whilst mere hobbyists like myself can easily get away with making up a > desired zener value from putting two smaller value ones in series to > add together their rated voltages, can such a dodge be employed by > professional designers without losing face? I mean, in the case where > there is no commercially available zener with precisely the desired > breakdown voltage? Would a pro designer be open to ridicule and > risking his rep by pulling such a stunt?
Win and others here have noted that zeners above 7V produce much more noise. You were in this thread too. Saturday, May 27, 2017 9:15 PM Subject: Combating Zener Jitter Jim Thompson wrote:
> AKA Flicker Noise > > Yup, pink noise. No jittering/jitterbugging involved. ;)
Winfield Hill wrote:
> Actually, I'd say you're wrong. The zener noise that we > see in avalanche mode (greater then 7 volts or so) is due > to step-wise "microplasma" ns-scale changes in current. > A decade or so ago we fully discussed it here on s.e.d., > complete with measurements, waveforms, detailed physics > paper references and the works. Nailed it down. As it > happens, the jitterbug analogy isn't so far off. > > This avalanche jitterbug noise source is not available > in the low-voltage field emission zener operating mode, > so using two sub-6-volt zeners in series in place of a > higher-voltage zener, or any of many other good schemes > would indeed be a good idea.
Tom Del Rosso wrote...
> Is the low-voltage noise less than half, so it > won't add up to more?
Winfield Hill wrote:
> Yes, it's a tiny fraction. Try it.
On Sunday, November 10, 2019 at 10:40:29 AM UTC+11, alan.ye...@gmail.com wrote:
> On Saturday, November 9, 2019 at 4:42:43 PM UTC-5, Cursitor Doom wrote: > > Whilst mere hobbyists like myself can easily get away with making up a > > desired zener value from putting two smaller value ones in series to add > > together their rated voltages, can such a dodge be employed by > > professional designers without losing face? I mean, in the case where > > there is no commercially available zener with precisely the desired > > breakdown voltage? Would a pro designer be open to ridicule and risking > > his rep by pulling such a stunt? > > But, is it really good practice to use only a stack of zeners? Should there not be a hi impedance bleeder path in parallel to each of the diode(s) stack so they all start to conduct and zener properly. Phil I'm surprised you did not mention this.
About the only problem with using a stack of zeners is running them at high enough current to prevent the avalanche process from turning itself off. The isn't a problem with low voltage zener diodes which rely on the Zener mechanism, but anything above about six volts is an avalanche diode. The volume in which the avalanche multiplication occurs is tiny, and if you operate at a current low enough that there's only one electron going through that region at a time there's a risk that it will get through without generating another pair of charge carriers, and the voltage across the diode will rise rapidly until another charge carrier gets generated by thermal noise. People exploit this effect by running zener diodes at low current to serve as noise sources. https://en.wikipedia.org/wiki/Noise_generator If you are very unlucky, a zener diode operating at low current can look as if it is oscillating at a few hundred MHz. We had a thread about this here many years ago. -- Bill Sloman, Sydney
 Bill Slowman wrote:

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> > > > > But, is it really good practice to use only a stack of zeners? Should there not be a hi impedance bleeder path in parallel to each of the diode(s) stack so they all start to conduct and zener properly. Phil I'm surprised you did not mention this. > > About the only problem with using a stack of zeners is running them at high enough current to prevent the avalanche process from turning itself off. > >
** My one problem was making sure 3W zeners had enough heat sinking so they did not de-solder themselves and fall right off the tag strip. Simple fix was to use more, lover voltage types. Damn those heavy metal guitarists !! ..... Phil