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Homework Help: Analysing Op Amp Circuit with a Photo diode

  1. Apr 18, 2010 #1
    For a lab we built the following circuit.

    Our photo diode was receiving a blinking signal which our op amp made visible on a DVM.

    I do not understand the purpose of the capacitors attached to the power rail.
    So far I understand how negative feed back with the Rf resistor controls the amount of gain. Without negative feed back the op amp would produce near infinite gain. The maximum voltage that can come out of the op amp is + or - 12V but about the capacitors I am at a loss.
    Any help would be appreciated.
    Last edited: Apr 18, 2010
  2. jcsd
  3. Apr 18, 2010 #2
    If you were using 12 volt batteries for your power supply the capacitors wouldn't serve any purpose. However power supplies connected to the mains have ripple and other noise, particularly switching supplies. With high gain circuits these imperfections are amplified and degrade the output. Those capacitors help clean up the power supply for the circuit.
  4. Apr 18, 2010 #3
    Thank you skeptic2.

    I just came across the word bypass capacitors that must be it.
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