Over voltage input protection

Thread Starter

Lucither666

Joined Feb 7, 2011
2
Hi, I have am designing a sensor that will be powered at 24V, switched through a relay and up to 4m of cable. When switched through a relay I experience an overvoltage of up to 40v due to the high rise time and cable length. The voltage regulator I am to use has a maximum input voltage of 32v.

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Looking at the available TVS's I cannot find a suitable one, one that allows a working voltage of 24v and a clamping voltage of approx. 30v. I also cannot seem to find any suitable over-voltage protection ic.

Does anyone have any advice for protecting the sensor from over-voltage?

Thanks.
 

Thread Starter

Lucither666

Joined Feb 7, 2011
2
FYI: I am looking into alternative voltage regulators that have a higher input tolerance. I am still interested in peoples thoughts though regarding this
 

MrSoftware

Joined Oct 29, 2013
2,015
This one might be too high, but it's the closest I saw at digikey. Reverse standoff of 25.6V, clamping at 36v:

If you're talking about tiny current, maybe trying a TVS with a reverse standoff voltage of 24-25v would work. Your spike may not reach the full clamping voltage, but maybe it will conduct enough over ~30V to suppress your spike? Great read on TVS diods here (TI datasheet).

Not knowing anything about the sensor, and guessing that your spike might be due to some inductance in the circuit combined with inrush current, maybe adding a small series resistor to dampen the inrush current would do the trick? Maybe put a series resistor and scope it just for a datapoint, to see if you really do have any inrush current. If this is the case, and depending on the current draw of the sensor, an ICL might be worth a look, but if your sensor doesn't draw much current then your ICL may remain high resistance, which may or may not be an issue.

So I guess you've got 2 options; (1) try to suppress the spike, or (2) try to figure out why the spike is happening and address the cause
 
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