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Common Mode Input Voltage

Discussion in 'Electronic Design' started by panfilero, Sep 11, 2013.

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  1. panfilero

    panfilero Guest

    I think this is right but wanted to make sure

    I'm looking at the LM321 OpAmp

    It says it has an input common-mode voltage range of V+ - 1.5

    page 3 of this datasheet

    I'm thinking that means that if I run this off a single supply of 5V and use it as a buffer, that I will be limited to an max input voltage of 3.5V, and that if I go over, I will probably see an output of around 3.5V.... so if I input 4V, it would basically saturate around 3.5V

    Is this right?

    so does my input common-mode voltage range tell me how close my output can get to the rail?

  2. panfilero

    panfilero Guest

    Cool, but what if I had say 1V at my input and a gain of 4, or something like that, where I'm not violating my input common mode voltage, does my output still not go to 4V?
  3. That's a different spec. and will depend on how much current you draw. The spec sheet will also tell you how close the output can can get to either rail. (with perhasp more than one load resistance)

    George H.
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