Folks,

There is a common problem: somebody will plug a wrong power supply (wall wart) with too high a voltage or wrong polarity. The agressor power supply may or may not have it’s own crowbar protection. This protection circuit looks like a simple reasonable idea:

The victim circuit by itself can survive up to 24V. During normal operation, it will draw up to 5A. Instructions for use prescribe a 12VDC supply.
PTC fuse: RGEF500, 5A hold current, 8.3A trip current, max time to trip is 2 seconds.
TVS diode: 13V to 15V. But... To be useful, the diode would have to survive at least 8.3A for 2 seconds. What’s the right way to select this TVS diode? For instance, would something like SMCJ13A have sufficient ratings (at least in principle)?

Any suggestion, insight or reference is really appreciated!

- Nick

 

I personnally would prefer to put an overvoltage protection circuit in there.

This can be easily done with 2x TL431 and a p-FET in series with the input of the victim circuit. Polarity protection could be a simple diode in series with the input.

I posted it somewhere here, if you don't find it I can post it again.

 

This can be easily done with 2x TL431 and a p-FET in series with the input of the victim circuit.

Part of the problem, which I didn't mention earlier, is that I'm constrained on board space. This requirement for protection is a last minute feature creep, so I want something quick & dirty.

Polarity protection could be a simple diode in series with the input.

Diode drop (even if it's a Schottky) is undesirable.