Questions about modification of a ground fault detector circuit

Thread Starter


Joined Jun 10, 2019
I think I should create another post with this question, but here it goes: the circuit attached is from an old device and it is used to detect 50/60Hz low ground fault currents from 20mA to 30A using a zero sequence current transformer. It varies the burden resistor and the gain resistor to deal with the large range of currents. I want to modify this circuit to use it with a microcontroller ADC in the range of 0-3.3V. My question is:

  1. Can I get rid of the dual power supply? I have two options: a precision rectifier, or doing rectification by software and just add a DC offset to the signal with a resistor divider network. If I were to choose a precision rectifier I'm eliminating the negative cycle of the signal, and I think that I need to read both cycles in applications like this?
  2. Do I need capacitors C3 and C4? They reduce the amplitude of the input signal.
  3. It seems like D3, R4 and C2 form a peak detector. I don't usually see this in CT conditioning circuits. I rather see a low pass filter at the op amp output.
  4. Do I need some sort of switchable gains amplifier to deal with this?

Any comments on simplifying this circuit will be appreciated.