[sdiy] Help deducing the internal resistor values of the IR3109?

[Jack Jackson]

So, if I understand correctly. Ill connect a potentiometer as a variable resistor between CAP and IN. +V, -V, and ground pins wired as normal. 

I'll take a DMM reading of voltage at CAP, and adjust the potentiometer until the voltages reads 0V. Then the impedance setting of the pot will mirror the internal resistor.

Is that right? Or do I take a measurement elsewhere?

Cheers,
Jack


>> I have 2 of these chips to hand. Can anyone think of a way to deduce the value of the resistors by taking measurements externally etc?
>
> I think so. If one makes the gain stage into a unity gain follower by
> feeding back the output by a variable resistor from CAP to IN terminal,
> one would find the minimum offset at some resistance setting.
> That should be close to the internal resistance. The output (=CAP) would
> sit near GND, because the + input is tied to that.
> For this to work one would also need to feed something into the CV input
> of course, to open up the gain stage.
>
> Cheers,
> René
>
>
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> http://www.schmitzbits.de/
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