Re: gEDA-user: always build a prototype!

[John Doty <jpd@xxxxxxxxxxxxx>]

On Aug 9, 2007, at 7:01 PM, Bob Paddock wrote:

> The subject reminds me of a question I've always wanted an answer to
> about circuit simulators, as in "always build a prototype".
>
> What do any of the circuit simulators give for this configuration:
>
> With the emitter of a 2N3904 or 2N2222 hooked to +12V through
> a 1k resistors, and the base grounded, what is the voltage measured
> from the base to the collector?  The collector is open.
>
> Any (NG)Spice/GNUCap etc. users out there that can try it?

Most (maybe all) Spice simulators can't go there because the usual  
transistor models don't do junction breakdown.

I've seen kilovolt transients in 350 nm MOS simulations with a  
commercial Spice. Physically impossible.

And just this week I've been tweaking GMIN in a Spice simulation to  
get a physically sensible result. With the default, some nodes were  
outside the power rails in a DC operating point analysis. Again,  
physically impossible. Understanding the physics and knowing how  
numerical methods can go wrong is essential in this business...

John Doty              Noqsi Aerospace, Ltd.
http://www.noqsi.com/
jpd@xxxxxxxxx




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