I built this design to measure AC power (attached). The voltage is measured pretty much the normal way only its stepped down to show about 1.4Vpp for 240V. The current is measured by measuring the voltage across the 4 milli-ohm shunt. The output that goes to the MCU has a DC offset of 0.7V which is then removed in the software. I simulated this in LTSpice and it showed the expected results.
I built this design today and while I was testing it I observed the following:
The VSENSE-N and ISENSE-N is where the DC offset of 0.7V is added however I measured -2.9V DC here. Also I see only the positive half of the AC voltage at the V-MCU pin and I'm not sure why.
The AC waveform at the I-SENSE-P pin is also offset by about -3V DC but I do not see any waveform at the I-MCU pin.
I used a 40W bulb as the AC load. The LMV324M is powered by a +/- 3.3V supply. The -3.3V comes from a charge pump dc to dc converter TC7660S.
What am I missing here?
I built this design today and while I was testing it I observed the following:
The VSENSE-N and ISENSE-N is where the DC offset of 0.7V is added however I measured -2.9V DC here. Also I see only the positive half of the AC voltage at the V-MCU pin and I'm not sure why.
The AC waveform at the I-SENSE-P pin is also offset by about -3V DC but I do not see any waveform at the I-MCU pin.
I used a 40W bulb as the AC load. The LMV324M is powered by a +/- 3.3V supply. The -3.3V comes from a charge pump dc to dc converter TC7660S.
What am I missing here?
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