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Reply-To: "Kevin Aylward"
From: "Kevin Aylward"
Subject: Re: Using inductor resistance as current sensor
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
Date: Wed, 2 Oct 2002 10:49:56 +0100
NNTP-Posting-Date: Wed, 02 Oct 2002 10:50:03 BST
"Graham Holloway" wrote in message
> "Kevin Aylward" wrote in message
> > "John Popelish" wrote in message
> > news:3D9A767E.432D2F1D@rica.net...
> > > I have had an idea for quite a while that I have never tested. In
> > > standard buck regulator, I think one could use the resistance of
> > > inductor to perform current limit or current mode control. The
> > > problem with it is that the small DC voltage drop is riding on the
> > > large inductive swing. But if the inductor was wound bifilar with
> > > heavy conductor and one very fine conductor, with both tied to the
> > > switch end, and only the heavy conductor tied to the output
> > > then the voltage difference between the downstream ends would be
> > > close to just the resistive drop of the heavy current carrying
> > > with almost none of the inductive EMF. A simple subtractor could
> > > reference and amplify this small drop to make a control signal.
> > > would save the need for a current shunt resistor and its
> > > voltage drop while providing instantaneous inductor current
> > > information. This measurement would have a positive temperature
> > > coefficient, but at least it would prevent thermal runaway.
> > >
> > > The post on the low drop current regulator brought this back to
> > > surface.
> > >
> > > Does this sound workable? Would anyone want to volunteer to
> > > it, or build it to try it out?
> > Interesting idea. Have you done a patent search on it?
> > I might have some time to check it out. I am actually working on a
> > little generic PWM subckt model right at the moment, can't have this
> > LTSpice getting all the glory in automatic PS design:-)
> I wouldn't have thought that a patent search was necessary. It has
> standard practice for as long as I can remember, to use a similar
> inductor arrangement (join the output-end wires together) on the
> noise inductors of SMPS's, to sense the output voltage, but without
> delaying characteristic of that final output filter.
> I would be surprised if this technique of current sensing was not in
> somewhere out there already, probably on a commercial PSU.
Maybe, I just have not seen it used in this manner before.
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.
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