AW: [sdiy] Zener-oscillators

[John L Marshall]

PUT, PUT, PUT!


Take care,
John
www.sound-photo.com
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----- Original Message -----
From: "harrybissell" <harrybissell at prodigy.net>
To: "Magnus Danielson" <cfmd at swipnet.se>
Cc: <Martin.Czech at Micronas.com>; <np at inverse-entertainment.de>;
<synth-diy at dropmix.xs4all.nl>; <micke at bmh.nu>
Sent: Monday, March 31, 2003 6:17 PM
Subject: Re: AW: [sdiy] Zener-oscillators


> Congratulations gentlemen
>
> I think you are well on your way to inventing the four-layer diode...
> maybe even the UJT ???    :^P
>
> H^) harry
>
> Magnus Danielson wrote:
>
> > From: "Czech Martin" <Martin.Czech at Micronas.com>
> > Subject: RE: AW: [sdiy] Zener-oscillators
> > Date: Mon, 31 Mar 2003 17:09:33 +0200
> >
> > Martin,
> >
> > > I've included a drawing of the transistor DC curve,
> > > as well as a curve tracer snap shot.
> > >
> > > It's only visible in heavily doped collector junctions,
> > > thus reverse mode operation.
> > > The thing is that the collector (it is the emitter!)
> > > base junction breaks down
> > > in avalanche. Once a certain amount of holes is in the base,
> > > it will turn on the emitter base junction in normal
> > > conduction and diffusion (emitter is really collector here).
> > > This current will diffuse to the collector where
> > > it will push the avalanche. Positive feedback!
> > > The voltage across the transistor will collapse,
> > > it will then look like a resistive branch.
> > > Go under the minimum voltage to sustain the avalanche
> > > and it will turn off.
> > >
> > > There is avalanche, "pushed avalanche", high injection
> > > and normal current amplification involved at the same
> > > time.
> > >
> > > Circuits that only want emitter to base zener will
> > > therefore not connect the collector pin.
> > >
> > > Before reaching the break over point, the leakage due to
> > > beginning avalanche will rise, if the current source
> > > can not live with this the circuit will hang there.
> >
> > OK. This starts to makes sense. The transistor emitter-collector
breakdown I-V
> > explains what happends.
> >
> > I've seen two recent reports of this type of oscillator actually
working.
> >
> > I've also tossed at BC550C under a 100 ohm resistor and a pretty good
sine for
> > straight and X-Y scope. Not a very elegant setup if you want a good I-V
curve,
> > but it does gives a hint. The breakdown is clearly visible and when you
drive
> > it as hard as -9.1 V it kicks in and bends in the other direction
pulling more
> > and more current falling back quickly to about -7.2 V which is a platau
under
> > which it pulls current (I drive mine as hard as -25 mA).
> >
> > A Zener-diode (6.2V out of a bag here on the table) has quite a
different
> > story to tell. So does the emitter-base setup. No, the emitter-collector
stuff
> > is what makes this fun.
> >
> > It's also interesting to see how the voltage of the base changes through
the
> > cycle. Near the abrupt slope it has about the same shape, including the
abrupt
> > slope. Looking at the base is like probing into the middle of all this,
since
> > it is the P between the N of the collector and the N of the emitter.
> >
> > Got to hit bed, oscillation is next lab-assignment for tomorrow!
> >
> > Cheers,
> > Magnus
>