"Ken Scharf" wrote in message
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I could put a germainium or low voltage drop si in series with
the VPP to block the negative voltage all together. That would
somewhat limit the vpp, which might be a problem.

I don't know definitively what you need here. A lot of older programmers
went through all sorts of hoops to be sure that value was above 12 volts.
However, lots and lots of folks have success with around 9 or so. I haven't
been able to find a spec, other than the maximum, but Microchip generally
refers to this as "13 volts".

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