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From: John Popelish
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Subject: Using inductor resistance as current sensor
Date: Wed, 02 Oct 2002 04:30:57 GMT
NNTP-Posting-Date: Wed, 02 Oct 2002 00:30:57 EDT
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?
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