The schematic I think is trying to show either terminate to V- with bypassing or just
to ground. The pic is confusing.
Those two amps not running open loop are they ? I dont see any fdbk around them....
If thats the case they would function not as amps buts a s comparators.
Regards, Dana.
R1 to R4 need to be very accurate and zero drift if the circuit in post #1 is to work reliably - often this is not the case - so that circuit is never used for original signals < 100mV .....
Hi,
There are "high side current sense amplifiers" they are optimized for this application .... and usually cheaper than INAmps.
Klaus
Hi,
I doubt that the input voltage at U4_+IN is correct. Please run a simulation.
The problem with the INA is not only the INA itself, it´s the high precision resistors your need. And even if you use a pot for calibration I expect thermal runaway. A high gain of 200V/V makes things worse. In the end it depends on your requirements/specifications whether the circuit is useful or not.
And I don´t like the "mistreating" of an OPAMP as comparator.
Klaus
No need to do it for me ;-)I simulated it for your benefit
They are often used. But they need the correct circuit. In your case moving from one side to the other should vary the "offset" just about a millivolt or so.Oofff, you mentioned the word trimpot in the same context as a precision circuit, it sent a horrible shiver down my spine just at the thought of it.
Your OpAmp diff amp circuit has unbalanced Gs in the inverting and non-inverting
paths, so is not rejecting CM.
Here I just tied the two inputs together and swept the input to see what the CM rejection
was with your R values. As you can see there is NO CMR from the circuit, so that swamps
out the contribution of the tiny shunt V.
Regards, Dana.
Hi,
No need to do it for me ;-)
They are often used. But they need the correct circuit. In your case moving from one side to the other should vary the "offset" just about a millivolt or so.
I meant the current shunt monitor. This is what I recommend to use.
Honestly I didn´t open the datasheets. I was mislead because "INA" often is used as an abbreviation for common "Instrumentation Amplifiers".
Mind the kelvin wiring at the miliiohms shunts.
***
Some thoughts:
* Is the "voltage good" threshold correct? It seems to be used for a 12V signal, but the threshod level is at 9V. And shouldnt it sense the voltage of the PV? means at the ANODE side of the diode?
* I recommend to use positive feedback at the comparators .. just to get clean edges without chattering.
* you may omit R11... and replace R10 with a (schottky) diode (cathode to U3). --> less components but improved voltage levels.
Klaus
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