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Thread: Industrial Electronics Problem [OT]
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face BY : Mark Willis email (remove spam text)



Not that I'm any great expert on RF, but this looks familiar.  One of
those "This one bites everyone" things that is good for "Breadth of
experience" for newbie & old-timer alike.

 It's probably not a ground loop, I'd guess you've looked at that!

 Here's MY best guess;  Is the capacitance of that shielded cable,
what's killing the 54C14J's?  That's in common between all the failing
parts.  And I know I've almost been BIT by this one before, driving
MOSFET's gate capacitances would have killed my 4000 series CMOS
circuits dead if I hadn't thought it through in advance.  (Current
limiting resistance...  Could be FET oscillation, I know I'm not an
expert on that just now <G>

 My "quick dirty" solution:  Split the 1k resistor at the output of
that shielded cable, into 2 resistors - one, say 100R, between the
54C14J and the cable, to limit 54C14J max output current, and the other,
say 900R at the input to the FET.  (You want to prevent both FET
oscillation and drawing too much current out of that FET.)  There's
probably a better optimized resistor value splitting to be done there,
there are some past posts in the PICList archives that covered this
IIRC.  (http://www.iversoft.com/piclist/ - I'd go look there.)  I don't
usually memorize solutions, just "Gotchas", and look up the solutions
when needed.  And check datasheets <G>

 Mark

Kelly Schauf wrote:
{Quote hidden}

<37371F33.859F4E45@nwlink.com> 7bit

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