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Understanding op-amps

  1. Jan 22, 2009 #1
    Hi can anyone help me get my head round how op-amps work? I know this is a silly question but ...

    Their functions (ie what a summing amp does etc) seem fairly clear. However maybe my question has more to do with the physics of what's happening but if the resistance between the two voltage input pins is practically infinite and the current is effectively being channeled, then why not just have a simple line instead of an op-amp component?
  2. jcsd
  3. Jan 22, 2009 #2
    I'm afraid I don't understand what you mean by "and the current is effectively being channeled", and by "why not have a simple line instead of an op-amp component".
  4. Jan 22, 2009 #3
  5. Jan 22, 2009 #4


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    Staff: Mentor

    The difference is the voltage gain of the opamp. There is very high voltage gain between the differential input pins and the output, so the output can have power gain compared to the input signal.

    So in a voltage follower, for example, if you just have a straight wire, the voltage gain is 1 and the current gain is 1, and there is no power gain. When you use an opamp in the voltage follower configuration, the voltage gain is 1, but the opamp's output amplifier stage can supply more current than the input signal can (generally), so there is power gain.

    The power gain is important for being able to process weak signals, and for driving power loads.

    Hope that helps. Read over the wikipedia page, and come back with specific questions if you have them. You might also see if your school library has a copy of "The Art of Electronics" by Horowitz and Hill -- the chapter on Feedback and Opamps may be helpful for you.
  6. Jan 22, 2009 #5
    the op-amp allows you to spy on a signal without being seen. ;)
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