Overvoltage protection

Hi everyone! I'm powering the logic part of my last circuit with my laptop's USB, and using 12V for the big stuff (some motors). Today happened that the 12V supply short ciruited the USB pins (I'm using a breakout board). Fornutaly, the USB was unplugged, and nothing happened, but since the board is all-time vibrating and moving I'm asking if there are some ways to protect a power supply for back overvoltage.
I've searched a little bit on the net and I've found TVS and MOVs diodes and tryristors, but as I understood they're designed for higher voltage than 5V, and for ESD strikes...
Do you guys have any suggestion?

P.s. I've alredy taken in consideration Zeners, but I need about 1A, and normal diodes (even schottky), but I don't think the logic will work with less than 5V.

Probably the best way to solve this is to place the 12v lines well away from the 5v and USB circuity and fasten them down so they can't move.

Any components that are installed to protect the USB Port will likely either affect the operation of the serial data stream or fry if the 12v shorts to them anyway. Thus the USB will be fried anyway.

You could also use a cheap hub that you don't mind sacrificing for isolation or get ahold of a USB Isolation board.

Glue it down if you don't want it to move.

Zeners seem like a good idea except they aren't. The leakage current is significant.

Try to keep an isolation perimeter. Everything coming into your Arduino box should be protected as close as possible to the point where it enters the box.

Protection for automotive circuits is more complex than other 12V circuits.

Thanks for replying!
Yes, I've alredy thought about glue and zip ties. At the moment they seem to be the only answer, but I'd rather use something electrical.

Any components that are installed to protect the USB Port will likely either affect the operation of the serial data stream or fry if the 12v shorts to them anyway.

I see it, but the two data wires are really short and quite far from the 12V supply. Something around Vcc should be enough...
I searched for some ICs with the charateristics of TVS but a lower voltage and I found these. Do you guys think are suitable for my application? The only limit I see is the 600mA maximum current, but I think I can reduce the consumption in some occasion.

Thanks again!

I think you're grasping for the notion of a crow-bar circuit.
A crow-bar is a voltage-trigger high-current switch that shorts a line to ground if it gets pulled too
high in voltage - not subtle, but can be an effective protection against overvoltage if the switching
device is fast enough.

However you need a crowbar circuit for every signal you want to protect, its not economical to
protect every signal in the system, and is typically used only for protecting a power supply rail,
for instance.

A crow-bar circuit has to be strong enough to win against your 12V supply too, given your scenario,
so would need to be rated accordingly.

For your scenario of 12V randomly touching things the only good answer is "make your entire circuit 12V" (in otherwords its not a scenario you should tolerate, stop it happening).

Thanks for replying. Yeah, I already evaluated the crowbar circuit, but discarded it: moneywise (both for component and PCB space), it's not what I'm looking for.
I'm getting more and more interested in the IC I've linked before. I've never used such circuit, have you?

If it's a mechanical problem, start by fixing it with a mechanical solution.

For example, water-proofing a circuit doesn't involve changing its schematic. You cover it with gunk to stop water from touching it.

If the vibration is causing things to loosen or move around when they shouldn't, stop them from moving around. Lay down some good beads of hot glue or epoxy. It can also act as an insulation layer so that even if something does get loose, it can't touch the covered parts of the circuit.

Yes, you're right, mechanical way in this case is the more suitable.
But now I'm curious about the electrical solution :slight_smile:

Subsea:
I searched for some ICs with the charateristics of TVS but a lower voltage and I found these. Do you guys think are suitable for my application? The only limit I see is the 600mA maximum current, but I think I can reduce the consumption in some occasion.

Certainly an interesting and useful IC, but please realise it is designed to protect the circuitry after the USB connection from over- (and under-) voltage via the 5 volt power line of the USB cable, not the other way round. Should a short happen on any other contact 12 volts is still going to run through your circuits and possibly even damage this protection chip too. The solution has to be physical, not electronic.

Also please bear in mind the small size of the device! And 600mA current handling looks to require the chip with the heatsink pad and a suitably designed PCB on which to mount it.

I can see potential in the chip, and other than cost considerations it would be ideal for automatic inclusion on the Arduino board in addition to the PTC poly-fuse That way the USB port is protected from over-current drain by the Arduino and its shields, and these in turn are protected from over-voltage from a faulty USB power supply.

Jim.

Hi! Thanks for replying!
I think I’ll buy it, and do a couple of tests. But yeah, a little bit of glue and zip ties will do the job :slight_smile: :wink: