op amp circuit help

Discussion in 'General Electronics Chat' started by kaznov, Apr 11, 2012.

  1. kaznov

    Thread Starter Member

    Mar 10, 2012
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    Hi guys
    for this circuit is't V0 due to V1 is just the non inverting circuit which is
    V0 = ( 1+ R4/R3) * V1 !! Becasue that's wht it seems like but my teacher told me that Vo due to V1 is just zero !!!
    any explanation please
    thanks
     
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  2. panic mode

    Senior Member

    Oct 10, 2011
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    opamp will do everything it can to ensure voltage difference at it's inputs is zero.

    since inputs are high impedance, there i no current in or out of inputs.
    using voltage divider we can write:

    Vin(-) = Vo*R3/(R3+R4)

    Vin(+) = Vin(-) = Vin

    (Vo-Vin)/R2 = (Vin - V1)/R1

    because current through R1 and R2 is same (recall - high impedance input of opamp).

    then use algebraic manipulation to get Vo as function of V1 (input voltage)
    should be something like this:
    [Vo-Vo*R3/(R3+R4)]/R2=[Vo*R3/(R3+R4) - V1]/R1
    [Vo-Vo*R3/(R3+R4)]/R2-Vo*R3/[R1(R3+R4)] = - V1/R1
    Vo{1-R3/[R2(R3+R4)]- R3/[R1(R3+R4)} = - V1/R1
    Vo = - (V1/R1)/{1-R3/[R2(R3+R4)]- R3/[R1(R3+R4)]}

    and then (after you get correct expression that looks something like previous line) you can play with it. for example you can calculate what happens when V1=0 or when all resistors are same etc.
     
  3. Wendy

    Moderator

    Mar 24, 2008
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  4. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    Hola Bill,

    Who wrote chapter 8?

    Whoever the author is, he did a good job. Found it easy to follow.
     
  5. panic mode

    Senior Member

    Oct 10, 2011
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    is that document maintained? the last update was some three years ago and there is still lot of work to be done.
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    Not me, but I have written other parts of the book.

    At the moment the editor is in absentia. I do expect him to eventually return though.
     
  7. atferrari

    AAC Fanatic!

    Jan 6, 2004
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    And what makes impossible to know his name?
     
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