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Reply-To: "Kevin Aylward"
From: "Kevin Aylward"
Subject: Re: LT SwitcherCAD Current Source Help
X-Newsreader: Microsoft Outlook Express 6.00.2600.0000
X-Inktomi-Trace: public1-pete2-5-cust19.pete.broadband.ntl.com 1031903552 5686 184.108.40.206 (13 Sep 2002 07:52:32 GMT)
Date: Fri, 13 Sep 2002 08:52:32 +0100
NNTP-Posting-Date: Fri, 13 Sep 2002 08:52:33 BST
"Jens Tingleff" wrote in message
> David Huhn wrote:
> > Hello,
> > I am a student working on a software model(in LT SwitcherCAD III)
> > motor driver and am trying to model the current chopping action of
> > FET driver IC that is going to be used.
> > I am trying to do this with a voltage dependent current source. I
> > read through the help and tried unsucessfully to come up with even a
> > simple tests.
> > Ideally, my current source would provide X amps if the voltage at
> > V_sense node is less than 3.4, and 0 amps if the voltage at the
> > node is greater than 3.4.
> One detail you might want to look out for:
> Many simulators do not handle discontinuous characteristics very
> is often much easier to have a continuous transistion between on and
> then an abrubt change. I have had problems with this on all my
> simulators :-(
> If you can use arbitrary equations to define the controlled source
> characteristic, you can put in an exponential function to smooth
> In this respect, the idea of using a switch element is not bad - if
> a non-zero on-resistance and a finite off-resistance, you will often
> that this simulates much easier than an ideal switch with
The spice SW voltage controlled switch is not discontinues. It varies
from its min value to its max value. You can not make it infinite. The
issue here is not one of discontinuity, but making sure that you don't
try and switch it in zero time.
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
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