Reverse polarity protection, better way without diode.

guiseppim · 14th May 2009, 01:47 AM

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!

wwenze · 14th May 2009, 06:25 AM

This is almost like a simple series voltage regulator, without the zener diode. BTW all our gear should have a voltage regulator, right?

peranders · 14th May 2009, 07:19 AM

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.

guiseppim · 14th May 2009, 02:57 PM

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.

MikeHunt79 · 16th May 2009, 09:01 PM

What are the reasons to avoid using a diode apart from the voltage drop?

Pafi · 19th May 2009, 08:44 AM

The unability to sinking current. (in case of supply pumping)

I prefer nMOS on the negative.

14th May 2009, 01:47 AM	#1
guiseppim diyAudio Member Join Date: May 2009	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!

14th May 2009, 07:19 AM	#3
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	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. __________________ /Per-Anders (my first name) or P-A as my friends call me

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14th May 2009, 06:25 AM	#2
wwenze diyAudio Member Join Date: Mar 2008	This is almost like a simple series voltage regulator, without the zener diode. BTW all our gear should have a voltage regulator, right?

14th May 2009, 02:57 PM	#4
guiseppim diyAudio Member Join Date: May 2009	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.

16th May 2009, 09:01 PM	#5
MikeHunt79 diyAudio Member Join Date: Aug 2003 Location: Bristol, UK	What are the reasons to avoid using a diode apart from the voltage drop?

19th May 2009, 08:44 AM	#6
Pafi diyAudio Member Join Date: May 2004 Location: Budapest	The unability to sinking current. (in case of supply pumping) I prefer nMOS on the negative.

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