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Basic Question about OP amp

  1. Jan 25, 2013 #1
    I understand how to apply op amps, but one thing about op amps had bugged me for some time. I want to know what about an op amp in negative feedback forces both the posotive and negative inputs to be equal. And could your explanation be for both an inverting and non inverting op amp.

    Thanks! :)
  2. jcsd
  3. Jan 25, 2013 #2


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    Welcome back to PF.

    If the (-) input were significantly lower than the (+) input, that would drive the output high, since [itex]V_{out}=A\cdot(V_+-V_-)[/itex]. And because of the feed back to the (-) input, driving the output high would raise the voltage at (-) input, driving it closer to the voltage at the (+) input.

    A similar argument applies to considering if the (-) input were significantly higher then the (+) input.

    Not sure what you mean here. Op amps are not "inverting" or "non inverting", those terms refer to the two inputs of any op amp. The explanation only works for feedback to the inverting input, that I refer to as (-) above.
    Last edited: Jan 25, 2013
  4. Jan 25, 2013 #3
    oh okay, that makes more sense now. I should've drawn that conclusion on my own, but i guess i was just being stupid.

    Thanks alot!
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