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Opto photodiode varicap?

Discussion in 'Electronic Design' started by Rich Grise, Oct 22, 2007.

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  1. Rich Grise

    Rich Grise Guest

    When a photodiode is reverse-biased, it has some capacitance,
    which has to be accounted for, right?

    If you reverse-biased the PHD in an optoisolator, would it
    become an isolated varicap?

    Conversely, just for fun, let's hear everybody's favorite
    easiest way to use optos for isolated gain control feedback. :)

    Thanks!
    Rich
     
  2. Tom Bruhns

    Tom Bruhns Guest

    Well, I suppose it would be isolated, and it is a varicap, in that its
    capacitance changes with applied reverse voltage. But what would vary
    in the diode, as you varied the LED current? Hint: not the
    capacitance, at least not by much. Consider that the width of the
    depletion region is set mainly by the reverse voltage applied to the
    diode. What happens when photons come zipping into that depletion
    region?

    Cheers,
    Tom
     
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