I need a schematic which senses AC Current (from IGBT) using a simple OPAMP and with gain adjustable. The output will be connected to PIC adc for displaying the load connected in the UPS.
You should put a resistor (a smaller one, like 1 ohm) in serie whith the current source. Then, you should use a operational amplifier to measure de voltaje drop across the resistor.
This circuit has a gain of 1 (1 mA on R results in 1 mV on Vo).
If you want another gain, here is the formula.
Considerate that you'll have a sine signal, that cross between +v and -v.
You should use a rectifier bridge before R to have a all positive signal.
After the operational amplifier, you can use a filter to have a CC level, or take equally spaced samples on your PIC (>> 100Hz) to reproduce the signal value.