trying to understand integrator op amp circuits

Discussion in 'Homework Help' started by RevitRed, Dec 7, 2014.

  1. RevitRed

    Thread Starter New Member

    Dec 4, 2014
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    [​IMG]

    this is the standard integrator circuit, can someone check if my understanding is correct please

    if we assume the the C = 1 mF
    the resistor is Rin = 10 kOhms
    the op amp will not saturate
    ideal op amp
    and input voltage is 10 V
    trying to figure out voltage out as a function of time

    the Vout is supposed to be -1/RC integral(Vin dt)


    Vout = -10/(10000 * 10^-3) integral(dt) = -10/(1) = -1t

    would this be correct?

    so Vout = -10t ?
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Since the opamp forces V(inv) to be 0V, the current in the 10K resistor is 1mA (10V/10K). The charge accumulated by the capacitor Q=C(ΔV) = it.
    Rearrange, ΔV = it/C = (1e-3)t/1000e-6 = (1e-3)t/1e-3) = t, or 1V/1s. However, the current flow causes the output of the opamp to go negative...

    93.gif
     
  3. RevitRed

    Thread Starter New Member

    Dec 4, 2014
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    thanks it seems as though your plot has confirmed my answer, by the way what program is it that you used to analyze this circuit
     
  4. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    LTSpice. Free download at Linear.com
     
  5. RevitRed

    Thread Starter New Member

    Dec 4, 2014
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    nice, thanks alot
     
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