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

[Jack Jackson]

Hi René,

I took the measurements as you suggested. I used a Bourns-3266 2K trimmer as a variable resistor. It was hard to get the cap voltage to sit at 0, as when I took my finger off the trimmer after adjusting it, it would jump up about 2mV. Eventually with it sitting at about +1mV, I took a reading of the potentiometer and it showed 432 ohms. So this would concur with what Bob Weigel said about them being in the 220 to 1K zone. 

I suppose to be more thorough, I should repeat the test on all 4 gain cells on both chips I have. One is date coded 777C and the other 775C, so it might give a decent enough range. For greater accuracy I could use a 500ohm trimmer, but I dont have any on hand.

Still 430 ohms sounds about right though.

Cheers,
Jack
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> Date: Sun, 6 Oct 2013 13:35:44 +0200
> From: uzs159 at uni-bonn.de
> To: jackdamery at hotmail.co.uk
> CC: synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] Help deducing the internal resistor values of the IR3109?
>
> Am 06.10.2013 01:14, schrieb 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?
>
> Thats the idea.
>
> Cheers,
> René
>
>
> --
> uzs159 at uni-bonn.de
> http://www.schmitzbits.de/