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 not
damage it.
Sean
At 09:53 PM 3/13/02 -0800, you wrote:
{Quote hidden}>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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