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From: John Popelish
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X-Mailer: Mozilla 4.7 [en] (Win98; U)
Subject: Re: Using inductor resistance as current sensor
Date: Wed, 02 Oct 2002 22:30:03 GMT
NNTP-Posting-Date: Wed, 02 Oct 2002 18:30:03 EDT
Harry Dellamano wrote:
> "John Popelish" wrote in message
> > I have had an idea for quite a while that I have never tested. In the
> > standard buck regulator, I think one could use the resistance of the
> > 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 one
> > heavy conductor and one very fine conductor, with both tied to the
> > switch end, and only the heavy conductor tied to the output filter,
> > then the voltage difference between the downstream ends would be very
> > close to just the resistive drop of the heavy current carrying wire
> > with almost none of the inductive EMF. A simple subtractor could
> > reference and amplify this small drop to make a control signal. This
> > would save the need for a current shunt resistor and its additional
> > 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 the
> > surface.
> > Does this sound workable? Would anyone want to volunteer to simulate
> > it, or build it to try it out?
> John, great idea but it has been done before. IBM first did it many years
> ago and maybe had a patent on it, since run out. There was a paper by David
> R. Pacholok in July 1990 PCIM called "Novel Current Sense Technique Boosts
> Converter Efficiency" that depicts your idea. I have used it a few times
> with good results.
> Another related scheme used by converters today is shown at the following
Interesting. Thanks, Harry.
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