Op Amp integrator problem

Discussion in 'The Projects Forum' started by aminhosseiny, Sep 4, 2015.

  1. aminhosseiny

    Thread Starter New Member

    Sep 4, 2015
    3
    0
    I made this op-amp integrator to have sharp edges triangular pulse in out out but this gives me something corrupted. Please help me to resolve my problem. The capacitor is not necessary so we could easily ignore it.
    [​IMG]


    [​IMG]
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,003
    3,232
    What are the supply voltages?
    The output of U3B is going directly to the summing junction of U1B, which won't work properly.
    A summing junction sums currents, not voltages, thus you need a resistor in series with the U3B output to convert its voltage to a current at the summing junction.
     
  3. cowades

    New Member

    Feb 6, 2012
    9
    1
    You don't actually have an integrator there. BTW Get C1 out of there.
    They look like this:
     
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  4. crutschow

    Expert

    Mar 14, 2008
    13,003
    3,232
    As cowades noted, I see no reason for C1.
    Remove it.
     
  5. aminhosseiny

    Thread Starter New Member

    Sep 4, 2015
    3
    0
    I told ya C1 is totally off the circuit and do not consider it. I just removed it and it did not work! You think it's not an integrator at all?
     
  6. cowades

    New Member

    Feb 6, 2012
    9
    1
    Here's another way to think about what crutschow said: the equation for an integrator is -1/RC where R is the input resistor and C is the feedback capacitor. You've got no input resistor (R=0) so the equation looks a lot like negative infinity.
     
  7. crutschow

    Expert

    Mar 14, 2008
    13,003
    3,232
    And I told ya you needed to add a resistor. :rolleyes:
     
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  8. aminhosseiny

    Thread Starter New Member

    Sep 4, 2015
    3
    0
    Well thanks. what will happen to R5? should I remove it? if not I just need to add a new resistor for U3B output?
     
  9. crutschow

    Expert

    Mar 14, 2008
    13,003
    3,232
    I see no purpose for R5 or R7 so they both can be eliminated.
    The resistor at U3B's output (U1A's input) is to provide the resistor to make U1A into a integrator with an RC time-constant, the new resistor being the R (assuming that's what you want).

    You seem not to understand how an op amp integrator works. Perhaps you should read up on that.
     
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