Re: [EE]: Bi-Directional 20A current shunt Using Single supply OPAMP

On Sat, September 13, 2025 1:20 am, Justin Richards wrote:
> Excellent suggestion.  I completely missed the fact that I have a 3.3V
> ref that can be halved.
>
> I originally chose to dismiss the use of a voltage divider as I expected
> it would affect and/or be affected by the biasing around Vin+ and the
> 12.8V as
> suggested would not be stable.
>
> But a relatively low impedance (1k ohms) divider across 3.3V is
> simulating nicely.
>


I assume you are using a pair of 1k in series to form the voltage divider
and then driving the 100k to the non-inverting input from the voltage
divider. You could reduce the parts count by just using a pair of 200k
resistors, one to +3V3, the other to ground, and the junction going to the
non-inverting input. This would have the same Thevenin voltage and
resistance. There MIGHT be an issue with noise on the 3.3V line being sent
into the amplifier through the voltage divider. This could be avoided
using the circuit you are apparently using and adding a capacitor to
ground at the voltage divider output. You could increase the resistances
used in the voltage divider some (as long as they are small compared to
100k). But, if the 3V3 is quiet enough, I'd just use the two 200k
resistors.

Harold
The ideal design has zero parts.
https://w6iwi.org


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