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Date: 09/05/03 at 2:59 AM
Posted by: Tomas
E-mail: tomas.linde@spray.se

Hi all!

I have a problem with my stepper driver card, it contains an AVR, a driver circuit, some LEDs, and inputs:
+32V, +5V, common GND, and also 4 IO inputs.

I want to protect all the circuits and the filter device, (diods and zener) agains polarity switching on the +32V input. It's no use to protect only the +32V and GND input because I have common GND so then current takes the way GND -> +5V or GND -> IO input and destroys something.

It has to be cheap so I can't protect every IO and voltage input. The only thing to do is to prevent current to run in the opposit direction in the common GND line, maybe a MOSFET transistor placed with drain - source in serie with the GND line or is there another way?

It has to cope with +32V gate to source, and the GND plane will rice with the voltage across drain-sorce whitch will effect the logic circuits ?

I'v never done this and wonder if it works ?

any ideas?

/Tomas

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