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From: Jens Tingleff
Subject: Re: LT SwitcherCAD Current Source Help
Date: Fri, 13 Sep 2002 07:48:34 +0100
Organization: ARSCC (tinarscc)
David Huhn wrote:
> I am a student working on a software model(in LT SwitcherCAD III) for a
> motor driver and am trying to model the current chopping action of the
> FET driver IC that is going to be used.
> I am trying to do this with a voltage dependent current source. I have
> read through the help and tried unsucessfully to come up with even a few
> simple tests.
> Ideally, my current source would provide X amps if the voltage at the
> V_sense node is less than 3.4, and 0 amps if the voltage at the sense
> node is greater than 3.4.
One detail you might want to look out for:
Many simulators do not handle discontinuous characteristics very easily. It
is often much easier to have a continuous transistion between on and off
then an abrubt change. I have had problems with this on all my favourite
If you can use arbitrary equations to define the controlled source
characteristic, you can put in an exponential function to smooth the
In this respect, the idea of using a switch element is not bad - if you have
a non-zero on-resistance and a finite off-resistance, you will often find
that this simulates much easier than an ideal switch with zero/infinite
Hope this helps
 I don't know SwitcherCAD features, but my remarks aren't really specific
to any one tool.
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