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OPA387: Differential Amplifier using opa387

Aswanth Mohanan
Prodigy 20 points
Part Number: OPA387

Tool/software:


Hello guys,

I had made a differential circuit for measuring ac voltage and current. In simulation the entire circuit is working and i am getting desired gain(6.8k/2.068M) for u1 ,gain(5k/1k) for u2. But in practical when i tried measure vrms value of 268 v i am only getting 228mv pk to pk instead of 1.24 v

.

can anyone help me on what i am doing wrong here?

  • 0
    TI__Expert 7530 points

    Hi Aswanth,

    I'd like to confirm a few things and I have a couple of follow-up questions.

    Have you tried probing the inputs to the op amp? If so, what voltages are you observing there?

    In addition, how are you building your circuit and what tolerance resistors are you using?

    Why is the op amp in the difference amplifier configuration when vmeas_neg and imeas_pos are system ground?

  • 0 in reply to HO SIU
    Prodigy 20 points

    the input is coming like .8v , so we made a pcb using a general purpose pcb and the tolerance of the resistor is 5%, when we tried single ended measurement the ac ground was interfering with out power supply, so we tried this.

  • 0 in reply to Aswanth Mohanan
    TI__Expert 7530 points

    Hi Aswanth,

    Was it +-0.8V on the non-inverting input? If so, it's strange that the output is not also +-0.8V since your configuration is around unity gain.

    Could you please show your setup and measure them to make sure that the resistor values are what is on your schematic?

    In addition, could you please provide an oscilloscope image with the non-inverting input and the output of the op amp probed?