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I'm currently simulating my high- side current sense amplifier for measuring mains current(along with the LP filter) .I also have the voltage sensing in the corner and I have attempted to simulate a realistic mains current magnitude of 15 A with a source and load impedance to avoid reflections.

I'm not sure why signal appears clipped even though the measured signal magnitude is less than the power supply range. How do I fix this? Is this getting saturated due to the high voltage in reference to ground?

Difference Amplifier

Difference amplifier

Whole schematic

Schematic

Signal through current sense resistor(green) vs output of difference amplifier Signals

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  • \$\begingroup\$ If you plot the current through R3 and R15 what do you get? Also, the S pin is shutdown`, not ground. It should be connected to either Vcc or Vee. \$\endgroup\$ Commented May 28, 2022 at 15:03
  • \$\begingroup\$ "Is this getting saturated due to the high voltage in reference to ground?" It will destroy the real opamp. Could you please explain why the load is split in two resistors and why low side sensing is not an option? \$\endgroup\$ Commented May 28, 2022 at 15:06
  • \$\begingroup\$ @devnull The resistors are to reduce the mains voltage to a level that the ADC can take in. Regarding the low side sensing, I've read that high side sensing is better for accuracy and fault detection which is why I chose it. Plus, low side sensing causes ground looping. Though the op amp I'm planning to use is OPA2960ID which has a relative high CMRR? In your opinion, will the trade-off for accuracy be that much of a difference or can it be compensated by op amp with high CMRR ... if I were to use low side sensing? \$\endgroup\$ Commented May 31, 2022 at 13:47

2 Answers 2

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Just put some voltage numbers on your front end and you'll see that things have gone wrong: -

enter image description here

And... the circuit will fry.

You need to rethink how you are going to achieve this and I would recommend low-side monitoring.

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    \$\begingroup\$ Might be worth noting, there are some comparators and in-amps that can handle voltages higher than their rails, but I've never seen an op-amp that can. \$\endgroup\$ Commented May 28, 2022 at 15:04
  • \$\begingroup\$ @Andy aka Echoing my comment I've read that high side sensing is better for accuracy and fault detection which is why I chose it. Plus, low side sensing causes ground looping. Though the op amp I'm planning to use is OPA2960ID which has a relative high CMRR. In your opinion, will the trade-off for accuracy be that much of a difference or can it be compensated by op amp with high CMRR ... if I were to use low side sensing? \$\endgroup\$ Commented Jun 1, 2022 at 8:59
  • \$\begingroup\$ @hellowurf what comment are you echoing? Low side sensing is simpler and ground loops can certainly be avoided. \$\endgroup\$ Commented Jun 1, 2022 at 10:02
  • \$\begingroup\$ @I meant to say it's been repeated in my question's comment section. What are the ways to avoid ground looping? \$\endgroup\$ Commented Jun 3, 2022 at 7:56
  • \$\begingroup\$ @hellowurf you adopt star-pointing of tracking to avoid ground loops. Or, you adopt isolation techniques such as using an isolated current sense device. \$\endgroup\$ Commented Jun 3, 2022 at 8:43
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Although the differential mode input is within +/- 5V, your common mode input is not. Hence the incorrect output.

You need to reduce the common mode input at the op-amp. Since R3 and R17 form a voltage divider, as do R15 and R14, you need to adjust the ratios so that the common mode voltage at the op-amp is within spec.

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