Opamp loop stabilty analysis

 

Hi attached here is an electronic DC load circuit. I want to do a loop stability analysis for this circuit. I mean I want to know Phase margin and Gain margin for the feedback loop.

How to do this analysis? I know that I should perform AC analysis but I don't know where should I inject or add the AC signal in the loop. Should I add AC signal at A, B, or C. Also should I ground the opamp inputs? and across what points should I see the output ie bode plot for gain and phase margin?

Please help me with this

Thanks

Santosh

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  • Hi Santosh,

    So, if I understand you correctly, you want to analyze the stability of this system. I'll give you a few thoughts.

    In General, it does not matter at which point in the loop to insert the signal source. But in your case, it doesn't make sense to add AC voltage source to point B, because the useful signal in this section of the circuit is the current and not the voltage.

    If you add a voltage source to the loop, ground the non-inverting input U1. You can also send a test signal to this input instead of inside the loop as an alternative. It doesn't matter for analysis.

    I think that it is most convenient to watch the results at the output of U1.

    Do you have any more questions?

    Regards,

    Kirill

Reply
  • Hi Santosh,

    So, if I understand you correctly, you want to analyze the stability of this system. I'll give you a few thoughts.

    In General, it does not matter at which point in the loop to insert the signal source. But in your case, it doesn't make sense to add AC voltage source to point B, because the useful signal in this section of the circuit is the current and not the voltage.

    If you add a voltage source to the loop, ground the non-inverting input U1. You can also send a test signal to this input instead of inside the loop as an alternative. It doesn't matter for analysis.

    I think that it is most convenient to watch the results at the output of U1.

    Do you have any more questions?

    Regards,

    Kirill

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