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Car ignition transient protection

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jdhar

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I need to power a device off my car's ECU +12V rail. When the car is starting, I would imagine that it's very inductive,and these spikes can be potentially harmful to a regulator that I have in line with the power. Either way, I don't want mad voltage fluctuations on the input, so how should I filter these out? I was thinking to either shunt them off with a Zener (which I read can be bad), or maybe use some sort of LC filter??
 

Buriedcode

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Hey, my analogue isn't really up to spec, but I've worked on cars. The voltage does indeed fluctuate, but not by that much. I'd use a bloody great inductor in series, and a large cap to ground afterwards. Then into a regulator, I imagine most regusltors are quite resiliant when it comes to peak voltage (30v+) so I'm sure you'll be fine. Although, nothing beats experimentation!! use a comparator set to +15v and +10V as a sort of clipping detector. With the output drive a trasistor with a cap to ground to strech the pulse, then an LED.

Hope this helps.

BuriedCode.
 

IanP

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Modern cars are not that bad, but any precaution wouldn;t heart.
You can use ≈1mH dc choke (as per attached picture), 1000µF (or bigger) capacitor, and, because car battery voltage is higher than 12V, you can use low-voltage drop 12V voltage regulator (similar to L4940-12: https://www.st.com/stonline/books/ascii/docs/2141.htm ).
regards,
IanP
 

sanJerry2004

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Everytime deal with pulse, u can consider filter(choke+capacitor).even ESD in interface.
 

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