>Hello,
>
>I need some real-world diode operation info.  I am simulating a circuit
>that has a comparator whose output is connected to a diode.  After the
>diode, is a zener diode connect to ground and I am interested in the
>voltage across the zener diode.  Now, when the compator is at the negative
>rail (-10V in this case) I am a little suprised to find that the voltage
>across the zener diode is -12mV.  Does a diode 'leak' some negative
>voltage?  Also, if I am going to connect the voltage across the zener
>diode to a PIC will the -12mV be considered a logic zero or will I damage
>my PIC?
>
>Regards,
>Donovan Parks
>
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> Hi Donovan,
>
> First of all, I'm curious how you made out with the FFT investigation?
>
> I think you are seeing diode reverse leakage current here. The zener (if
> connected as usual) is forward biased here and your regular diode (I'm
> assuming) is reverse biased. Most of the -10V appears across the regular
> diode and causes a tiny current to flow (probably a few tens of nanoamps).
> This current is forward current for the zener and corresponds to a very
> small forward bias (12mV in this case). A forward bias on the zener means
> that the "top" connection is more negative than the bottom and since the
> bottom is grounded, the top would be 12mV less than ground or -12mV.
>
> No, this should not damage your PIC. In the worst case, all of the reverse
> current would flow into the PIC input and certainly a few nanoamps will