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Homework Help: Non-Inverting Non-Ideal OpAmp Gain

  1. Sep 15, 2010 #1
    The first part of this problem was to find the gain using an ideal OpAmp.
    I am on the second half of this homework problem, where we find Vout/Vin, aka Gain, using a non ideal OpAmp. The attachment is the picture of the circuit.

    I know that since the OpAmp is no longer ideal A no longer goes to infinity, which provides a small input on the negative terminal. So, this is what I have right now...but its not getting me to the correct answer....

    Vout*(R2 / [R1 + R2]) = Vin + Vout/A


    Is this how I would start to find the gain? Once i get Vout/Vin, I could take the lim as A goes to infinity to verify that, the gain equals the ideal OpAmp.
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     

    Attached Files:

  2. jcsd
  3. Sep 17, 2010 #2

    gabbagabbahey

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    Homework Helper
    Gold Member

    An Op-Amp multiples the difference between the voltage into the positive input and the voltage into the the negative input by its open-loop gain [itex]A[/itex]. In other words,

    [tex]V_{\text{out}}=A(V_{+}-V_{-})[/tex]


    What are [itex]V_{\pm}[/itex] for the circuit in your diagram?
     
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