Re: gEDA-user: zener diode modeling

[Andy Fierman <andyfierman@xxxxxxxxxxxxxxx>]

Hmmm.

Tricky things zener, schottky and soft recovery diode models ...

Try a different vendors model (check to see if it is actually a
different model)?

You could try using a V (voltage) source in series with an ordinary
diode plus a second diode in anti-parallel with the series V and
diode.

This will give you a high reverse drop and a forward drop of a normal
diode.  The V source is set to the zener voltage minus one diode drop.
So if you wanted a 5.6V zener, you set V to about 4.9V and assume
about a 0,7V forward drop in the diode. You can play about with the
value of V to set the overall drop to where you want it because you
don't know exactly what the diode drop will be as it will depend on
the diode model and of course the forward current.

Or you can start with your existing zener model and play about with
the parameters to see if you can make it work.

If you make yourself a simple test circuit such as a pulse source with
some series R driving the zener with maybe some C in parallel with the
diode you can run transient tests on it to make sure you've not set up
silly capacitance or transit times or messed up the forward or
breakdown voltage to much whilst still giving you something that
behaves like the diode you might expect.

Beware stripping the model down too far though. If you take out too
much of the realistic diode, you may end up with an idealised device
that has inherent 2nd or even first order discontinuities that will
make your convergence problems even worse.

Silly question though: have you tried putting a 1G resistor in
parallel with it? Or adding a few nH in series to model some lead
inductance?

Often the more realistic the circuit is the better it converges.

Cheers,

         Andy.

signality.co.uk



On 18 April 2011 18:02, yamazakir2 <yamazakir2@xxxxxxxxx> wrote:
> Does anybody have a nice and simple zener diode model they would like
> to share? The model that I am using has trouble with convergence in
> context of a complicated switching circuit with ngspice.
>
>
> _______________________________________________
> geda-user mailing list
> geda-user@xxxxxxxxxxxxxx
> http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
>


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