Re: gEDA-user: zener diode modeling

[yamazakir2 <yamazakir2@xxxxxxxxx>]

I have not used a parallel gig ohm resistor or series inductor, but I
have tried tweaking component sizes and it is extremely hard to get
zeners to not gag in the middle of a transient sim I was looking for a
very generic all purpose model that won't yak. It doesn't haven't to
be accurate, just work.

On Mon, Apr 18, 2011 at 1:38 PM, Andy Fierman
<andyfierman@xxxxxxxxxxxxxxx> wrote:
> 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.
>>
>>
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>
>
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