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Old 09-11-2013, 10:28 AM
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wasyoungonce (Brendan)
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wasyoungonce is offline
 
Join Date: Jul 2006
Location: Mexico city (Melb), Australia
Posts: 2,357
Hi Chris, most excellent work...one thing I noticed...DEW controllers using RCA connectors.

You have designed the system as a low side switch I'm not sure if you are controlling the TC4427 outputs with PWM (I suspect you are) or just switching the MOSFETs on/off.

If you are PWM controlling the FETs then...if applied power driving the mosfet is low, the outside shield of the RCA can approach +12V.
Touch this against any part of the mount (earth) then there is a short cct to earth.

Somewhere back in the dark ages someone used RCAs for DEW strap connectors and this became a pseudo standard...a poor standard at best, especially if the RCA plug is a metal one, like some used by Kendrick. Although I have seen some of these covered with heatshrink.

The best fix.... use a high side switch MOSFET (wire the RCA shield to grnd, thus will always be grnd) like AUIR3315 (or called IR3315), 3~30A programmable shutdown (via resistor) high side switch...even has rev polarity protection...no fuse needed!

I have tried them...they work a treat and impossible to destroy once I shutdown set. Specifically they are designed for Automotive work, thus ideal for +12V systems. There is a range of these FETS, IR3313 ~IR3317 that have varying properties specifically the IR3315 is best (~$3.9 in to220 format) due to the low on rds and I shtdwn can be as little as 3A. If a dew strap is using more than 3A...then well yikes!

Sorry for the long read...

Brendan
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