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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:

enter image description here

That's the schematic I've made:

enter image description here

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?

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  • \$\begingroup\$ Hi Rhode: You really don’t get any isolation if the op amp on the input side shares a power supply with an op amp on the output side. You need to somehow provide isolated power for that op amp. ( A battery would work for a few hours). \$\endgroup\$
    – user69795
    May 20 '20 at 23:29
  • \$\begingroup\$ @user69795 they won't share a power supply. I'll use taps of an isolated transformer to make two power supplies. I tried to point that using the (1) and (2) in the GNDs and +12V, +5V. \$\endgroup\$
    – Rohde
    May 20 '20 at 23:47
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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.

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