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How does positive feedback works in opamp circuits?

  1. Jan 12, 2007 #1
    I was wondering,how does positive feedback works in opamp circuits?Like is there any formula for calculating positive feedback?I know that with negative feedback we have Vp=Vn but I don't know how it works with positive feedback!Thanks for the reply!
  2. jcsd
  3. Jan 12, 2007 #2


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    Staff: Mentor

    The only times that I know of that you use positive feedback would be for oscillators and to add hysteresis to a comparator circuit. And with the oscillator, it's still feedback to the - terminal, but with a 180 degree phase shift.

    Here is a good explanation of positive feedback for comparator hysteresis:


    As for your specific question, just remember that the key feature of the opamp is its high gain from input to output. For the situation of negative feedback, that forces Vn = Vp. But for positive feedback, it just locks the + input at some voltage, determined by which way the output pins, and what the resistor divider looks like from Vo back to the + input.
  4. Jan 13, 2007 #3
    Go to http://ocw.mit.edu/OcwWeb/Electrical-Engineering-and-Computer-Science/6-002Circuits-and-ElectronicsFall2000/VideoLectures/index.htm" [Broken]
    and watch the postive feedback lecture.
    Last edited by a moderator: May 2, 2017
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