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My op amp doesn't work well under AC input

  1. Aug 20, 2014 #1
    The type of op amp I am using is Voltage-to-Current Amp.

    Under DC voltage input, it works perfectly well, boosting the current of a signal generator (DC mode) up to 250mA with the help of single supply working at 25V.

    However, when I turn the signal generator in AC mode, hoping to achieve AC current oscillating between the value of +125mA and -125mA by adjusting the offset, I found that the negative current won't decrease.

    By decreasing the offset, the positive value keep decrease (from 250 to 200mA), but the negative one get stuck at -4mA.

    When the offset is lowered to a certain value, the positive value suddenly drop to negative.

    I have no idea what's going on. It is my first time to play with a op amp, I didn't expect it to be so complicated.
  2. jcsd
  3. Aug 20, 2014 #2


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    2017 Award

    hi there

    well lets start by you giving us the actual type of Op-Amp ( model #)
    then lets get a circuit from you that you are working from
    Then a photo or 2 of your actual made up circuit

    Then some of us may be able to see if you have made an error either in your circuit or construction etc :smile:

  4. Aug 20, 2014 #3


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    Indeed, we don't even know what frequency you are operating at, or if you are slewing.

    Analog circuits are a bottomless pit of complexity.
  5. Aug 20, 2014 #4


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    Well said!
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