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window comparator using a single op-amp

Discussion in 'Electronic Basics' started by Lee, May 8, 2005.

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  1. Lee

    Lee Guest

    does anyone know a circuit of a window comparator using only a single
    op-amp...i need a shematic for this...tnx
  2. Bob Monsen

    Bob Monsen Guest

    Hmmm. There was a posting on recently asking for
    the same thing. Go look there.
  3. ryan wiehle

    ryan wiehle Guest

    same user
  4. Rich Webb

    Rich Webb Guest

    Same homework question.
  5. Bob Monsen

    Bob Monsen Guest

    In that case...

    | |
    | |
    [220k] [100k]
    | |
    | |
    | |
    .->|--o-------(--- Inverting Input
    | | |
    Vin-o | |
    | | |
    '----(---|<----o-- Noninverting Input
    | |
    | |
    [100k] [220k]
    | |
    | |
    | |
    | |
    | |
    | |

    The output of the comparator will go high when Vin is between 2.5V and
    7.5V. The things in [] are resistors. The ->|- are diodes. It should be
    viewed using a fixed space font, like courier. Otherwise, nothing lines up.

    You get to set the window by changing the resistor values. The low
    window limit is set by the left two resistors, whereas the high window
    limit is set by the right two resistors.

    As the input increases from 0, the noninverting input first follows the
    input at 0.7V above it. The inverting input is fixed at 3.125V. Once the
    input gets to be 2.5V, the output of the comparator will go high, since
    the non-inverting input will then exceed the inverting input (which is
    still fixed at 3.125V.)

    As the input continues to increase, once it gets to 3.125 + 0.7V, the
    inverting input will start to rise. It's still 1.4V lower than the
    non-inverting input, so the output is still high.

    When the input gets to 6.875-0.7V, the non-inverting input will stop
    increasing. The inverting input will continue to climb as it has been
    doing. Once the input gets to be 6.875+0.7V, the inverting input will be
    larger than the now fixed non-inverting input, and the output will go low.

    Thus, the output is high when 2.5V < Vin < 7.5V.
  6. Bob Monsen

    Bob Monsen Guest

    I don't have a problem with folks asking homework questions. Electronics
    is part theory, part recipies, like all engineering. Sometimes, the best
    way to proceed is to ask.
  7. Rich Webb

    Rich Webb Guest

    I don't have a problem with it, either, providing that the poster
    demonstrates that he has invested some effort into solving the problem
    himself. The goal isn't the answer to the question, it's the method of
    solving it.
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