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From: "Harry Dellamano"
Subject: Re: Using inductor resistance as current sensor
Date: Wed, 2 Oct 2002 10:35:45 -0700
Organization: Posted via Supernews, http://www.supernews.com
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"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
> Does this sound workable? Would anyone want to volunteer to simulate
> it, or build it to try it out?
> John Popelish
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
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