Anyone know of a prefabbed TVS array with screw terminals?

[mwebster]

I've got a TTL level digital input card that's started popping channels. I suspect a wiring fault in our cabling or test unit is temporarily tossing 24VAC onto the input line which the input card can't hold off.

So, I'm looking for a protection solution somewhere this side of full-blown isolation ($30x18 channels is a little more than I'd like to spend + I have limited room in the system).

It seems to me an ideal solution would be an array of zeners like in a TVS diode array. I just need the voltage from any intermittent shorts held off the input pins long enough to blow the 1A quick-blow fuse on the 24VAC line. I've found IC's that should work for this for $2-3, but I'd rather not spin a PCB if I don't have to.

Does anyone know of a PCB or DIN-rail mounted solution for a problem like this for less than $300 or so?

 

[ScottyUK]

Quick & dirty way to do it would be a Transorb or similar fitted within a double-deck DIN-rail terminal. I know Weidmuller, and probably Phoenix and Entrelec too, offer a ready-built part with a regular diode - probably a 1N4004 or similar - fitted within the terminal, so it should be fairly easy to make your own.


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If we learn from our mistakes I'm getting a great education!

 

[VEBill]

There's the ol' SCR crowbar circuit.

The SCR is across the line and its gate is connected to a simple little circuit designed to trigger the SCR when the voltage exceeds the adjustable limit. The SCR dead-shorts the line when triggered. The circuit typically requires some careful attention to bypassing to prevent false triggers.