[sdiy] Zener-oscillators

[Magnus Danielson]

From: "Czech Martin" <Martin.Czech at Micronas.com>
Subject: RE: [sdiy] Zener-oscillators
Date: Mon, 31 Mar 2003 16:11:37 +0200

> Hi Magnus,

Hi Martin,

> I understand that you want to build an oscillator with
> a zener diode from shelf and a capacitor.

Want and want... I am investigating the concept. You should see by my list of
issues that I suspect many forms of defects, the severity of them remains to
be quantified. This have never excluded major defects.

> I think that this will not work. The zener diode
> as such has a continuous V/I curve, even in avalanche
> region. It has no current amplification, hence no snap 
> back or other switching action like the npn in avalanche
> (emitter-base breakdown).

Interesting point. I have yeat to dig deeper into the books. I've only seen
the reversed-transistor mode.

> I think that the supposed circuit will only run into
> the avalanche limitation - and stay there for ever.

If you where using a Zener-diode then, but using a transistor in Zener-mode
would make it work, right?

> The other statements are correct, the npn relaxation 
> oscillator will have sometemperature coefficent issues
> as well as leakage issues. Therefore the range of operation
> is limited.

Yes, but I wanted to have those properties quantified. Let's say we find that
there is a certain flaw here and a certain flaw there... then comes the
question if those flaws can be compensated one way or another. This is again
a mind-twister. You learn why you are doing something by learning why you are
not doing it another way, but only then you know _REALLY_ why you are doing
something one way.

See my point?

So, OK... pure Zener would probably not cut it but a reverse transitor would,
not a big deal in my book. OK, so just how bad is this thing if we start to
look at it? Is there any quick tricks to improve it and how much better is
reasnoble to expect?

Also, the field of usage may not be great, but it could never the less be
usefull, then we have another trick to pull out of the hat. OK, decent
behaviour over an octave or two ... there is still uses for such knowledge.

Cheers,
Magnus - finds a joy in thinking differently at times...