Dumitru

Since you have a voltage monitor available, you could just
periodically switch the incoming supply off with a FET or bipolar and
measure the time an (electrolytic ?) capacitor takes to discharge to
the threashold point. (Then switch it back on again)
You would need to know the value of the cap and also it's temperature
coefficient.

Or you can calibrate against a known bleed resistor or current.

This method would be more suited to low currents.

RP

On 02/06/06, Harold Hallikainen <harold@hallikainen.com> wrote:
>
> >
> > Note that the voltages you'll be dealing with will be on the order of 0.1V
> > (probably a lot less than that, actually), so you'll need to amplify the
> > signal. A single opamp can do it - you want a differential-input amplifier
> > circuit. A gain of about 20 should do it.
> >
>
> On high side sensing, you need to have a pretty good CMRR on your
> differential amplifier, which requires very precise resistor matching.
> There are "current sense" amplifiers specifically for this purpose. I've
> used a Maxim chip for this purpose (see
> http://para.maxim-ic.com/cache/en/results/4884.html). Linear Technology
> also makes them (see
> http://www.linear.com/pc/viewCategory.do?navId=H0,C1,C1154,C1009,C1077).
> I'm sure there are also others.
>
> I used the Maxim part to regulate the current into a high power LED (about
> 10W). The output of the sense amplifier drives the feedback input of an
> LTC boost regulator.
>
> Harold
>
>
>
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