I'd like to measure 0-800VDC using the ADC of a PIC18F and opto-isolated from the high voltage. Since optocoupler's CTR is variable and non-linear, I'll use the IL300. Checking this application note, I've found the following schematic:
That's the schematic I've made:
From that, I'd like to understand what parameters I have to check to choose the right op amps for this application. Any general purpose rail-to-rail 12V single supply would fit the project? Also, is IL300 the best option for this?
The op-amp is non-critical- it just needs to be able to drive a few mA through the LED, and it needs to be "single supply" (input common-mode range includes ground) unless you have bipolar supplies. And reasonable bandwidth.
IL300 does not make a particularly good isolation amplifier, the gain mismatch is 0.56 to 1.65 so it definitely requires calibration (your 800V could read as 448V or 1320V or anywhere in between, plus resistor tolerances), and it can shift several percent for temperature changes.
You might want to consider buying a commercial isolation amplifier or digitizing the signal and passing the value over the isolation barrier in digital form.
Many optocouplers like IL300 has many tolerances and mismatch sources. Like temperature, lifetime (LED aging), produciton tolerances (between two PDs).
Use better a resistor divider on the voltage rail and then use an isolated sigma-delta modulator. Something like AD7503 or ADUM7703. This should be much easier to control. There are also analog isolators like ADUM4165.
