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Old 14th May 2009, 12:47 AM   #1
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Default Reverse polarity protection, better way without diode.

It's not very safe to run equipment without this protection. I've burned a few things up plugging them in the wrong way. Needs only a P channel power MOSFET and one resistor.
I've tested on TA2024 board, replacing on board diode. Voltage drop measured as .02v at idle with the mosfet I used, an SFP9644 salvaged from a broken monitor. I haven't had a chance to listen yet.

A link to the original article:

MOSFET reverse polarity protection


I think this should be fine with just about any gear, as long as you choose a suitable mosfet? And double check the GDS pinouts!
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Old 14th May 2009, 05:25 AM   #2
wwenze is offline wwenze  Singapore
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This is almost like a simple series voltage regulator, without the zener diode. BTW all our gear should have a voltage regulator, right?
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Old 14th May 2009, 06:19 AM   #3
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You run current backwards through the mosfet and since you have signal on the gate you won't get a diode voltage drop. You'll get only Rdson * I.
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Old 14th May 2009, 01:57 PM   #4
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It doesn't mention it on the link I gave, but the 1M ohm resistor, I believe, produces a soft start delay of about 100ms. Probably not that important, but could be useful if it can be tweaked further.
It seems to do the job well enough.
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Old 16th May 2009, 08:01 PM   #5
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What are the reasons to avoid using a diode apart from the voltage drop?
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Old 19th May 2009, 07:44 AM   #6
Pafi is offline Pafi  Hungary
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The unability to sinking current. (in case of supply pumping)

I prefer nMOS on the negative.
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