Reverse polarity protection diode causes more harm than good?

[soggybag]

I saw this post on the gear page where Zvex is talking about removing the reverse protection diode because he found it caused more damage than than without.

There has been some concern expressed about a diode being "clipped" out of the circuit on the Vexters. This is because we stopped soldering it into the US-version and had a number of Vexters on hand that needed to be altered to be the same way. This diode is part of the power supply and does not affect the audio. It's to protect the circuit from reverse-polarity power supplies, but we discovered that when used with a high-powered supply it causes more harm than good, and in normal circumstances the circuit will survive a reverse-wired supply without any harm anyway.

http://www.thegearpage.net/board/showthread.php?t=285405&highlight=zvex&page=2

What's the deal here?

[R.G.]

I'm not sure what he means. For most situations and most power supplies, the shunt-reverse diode is OK.

The reversed power supply diode is not for all situations and it's not a slam dunk protector. Maybe that's what he means. I can postulate that if you had a power supply that had enough current capability to burn out the diode, that you could damage the PCB.

We periodically get calls about a 1Spot killing pedals, so we have deliberately tried setting up a 1Spot (1.7A of 9V) in reverse polarity onto a number of pedals. Result? No damage whatsoever, after hours of reversed current. That's probably because the 1Spot has designed into it a "restart" where if it can't bring the output voltage up within X time, it shuts down and starts over. So it will not just sit there and cook something unless it pulls less than 1.7A.

Other power supplies may not have such good manners.

The other thing that can happen is if you put a 9Vac supply onto a DC pedal. This burns out the reverse diode, then burns a hole in the PCB where the diode used to be. Maybe that's what zv means.

Our new line of pedals has a series protection circuit designed into it that is immune to not only reversed voltages, but also the 9Vac "Power Supply of Death".

It's also possible that there is some quirk of the circuit zv is discussing that is fragile in some way. No way to tell.

[soggybag]

Sounds like it might be a situation where the diode would be ruined if the power was reversed. Maybe the rest of the pedal might survive without it. Removing the diode might keep a lot of pedals from being returned just to have the diode replaced.

[Pushtone]

Other power supplies may not have such good manners.

I pick up a 1Spot this summer, love it.

I notice is also has a delayed turned on feature.
Takes about one full second before the pedal LED lights up after energizing the 1spot.

My Boss PSA doesn't do that.




I think I'll still be putting in diodes for reverse polarity protection.

[soggybag]

Probably depends on the circuit. I'm willing to bet some circuits can suffer reverse polarity with little or no damage. While some parts in other circuits are very sensitive to reverse polarity.

I have enough trouble understanding what is going on when the power is connected in the proper direction. It would be very hard for me to predict what would happen if the power were reversed.