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
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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