Maixium voltage on a input pin

[Demon]

The only problem i see with the use of the 7805 series voltage regulator is its min and max operating tempratures. Min of 0 deg C and max of 85 deg C is not suitable for an automotive environment. You need -40 deg C to +125 deg C.

Try a LM2937ET-5.0 or, a LM2954AIT-5.0 if you require an output voltage tolorence of 1%. You will need i/p and o/p caps with both parts or you will see near supply voltages at the output. I have used everything from 0.1uf to 330uf at the output on both parts and it always works fine. Remember to spec your input cap with a minimum of 35v.

Here is an example of what i am using on a tyre pressure control system for a semi:-

LM2954AIT-5.0
AAvid heatsink 592502B034
input cap - 220uF 50v Panasonic EEVFK21H221P
output cap - 330uF 25v Panasonic EEVFK1E331P

All available from www.digikey.com

Probably overkill but safe as houses.

Sadly the LM2954AIT is not longer available at DigiKey, I checked both the Canadian and US pages, even for LM2954 without success. (I just checked for the LM2937 and it is available)

Gonna search and see what else they have with automotive specs.


EDIT: It's not obvious searching for a voltage regulator for an automotive application on DigiKey, it's not part of the description. The fact that each manufacturer uses a different naming standard for the part series does not help either.

Also, using a 5V voltage regulator isn't going to help my case. I'd like to sense signals from various sensors on an old car, they are fed from the 12V battery. Even if I can lower the VREF from 12V to 5V, I won't be able to use the same technique for the signal from the sensor which can vary between 0-12V.