AVR-Chat

At 04:58 AM 7/9/06 +0000, Ryan wrote:
>Thanks, I know exactly what you're talking about.  However, for
>someone who might inadvertantly connect a +12V supply to the pin... It
>would obviously try to sink lots of current through the diode, likely
>blowing it up, then blowing up the MCU.  Would the effectiveness be
>reduced by putting series resistors (say, 1k?) with the two diodes?

Generally the effectiveness of the protection will be increased by placing 
a resistor in series with the diode pair.  A second series resistor after 
the diode pair further limits the fault current to the MCU so that it 
doesn't latch or fry "to protect" the protection diodes.  Also take a look 
at using a polyswitch as a supplement or replacement for the resistor so 
that under severe faults the circuit opens and protects the power supplies 
and the protection devices.  All that doesn't really deal with EFTs but 
should provide protection to some level of misconnects.

Robert

" 'Freedom' has no meaning of itself.  There are always restrictions,   be 
they legal, genetic, or physical.  If you don't believe me, try to chew a 
radio signal. "  -- Kelvin Throop, III
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