At 02:35 PM 5/16/01 -0400, you wrote:
>> One of the things I'm looking for in conjunction with the battery charger
>is
>> a good low-side (preferably) or high side current measuring schematic.
>I'm
>> envisioning an op-amp capable of rail-to-rail inputs, across a small sense
>> resistor between batt- and ground, maybe with a little low pass filtering.
>> Tried to whip this up in Spice and can't get it to work.  Anybody seen a
>> good schematic for this application?  I'm SOOOO rusty on analog...
>
>I was going to do this on the high side.  The current sense resistor is
>going to double to also limit the maximum possible current and reduce the
>dissipation in the current regulator.  All you need to to turn this into a
>ground-referenced signal proportional to the current is a diff amp.

Or create a current source from the postive rail, controlled by the
voltage across the sense resistor. That allows the signal to be shifted
to the low side without requiring precisely matched resistors. You do
need an opamp with rail-to-rail inputs, a PNP BJT and a few resistors.

Best regards,
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Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
Contributions invited->The AVR-gcc FAQ is at: http://www.bluecollarlinux.com
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