Automobile Project (Electrical Parts Requirement)
 

Hello,guys. I'm looking at putting together a circuit board to be used in an automobile. It will only be connected to a 12 V and ground. Everything else will be internal to my board.

I was planning on putting a 12 V regulator up front to make sure I could rely on clean power for my design and found a few that seem to be rated for cars. While looking for regulators I stumbled on automotive grade regulators.

Here is one from kynix: 12 V - 497-10192-1-ND (LD1086DTTRY, IC REG LDO ADJ 1.5A DPAK, -40°C ~ 125°C)

I know that they're designed to protect the downstream circuit from possible voltage dumps (or surges) from all the electrical noise found in a car.

Anyway this brought up a whole set of questions, but the main one was this: As long as any external connections between the electrical system and my board are bridged with automotive grade components (and I stay out of extreme climate areas found in/around cars) can I just use regular off the shelf components?

Or do I need to find automotive grade for everything?

For example, if I'm trying to use this circuit:
http://i.stack.imgur.com/Dq0PR.jpg
Can I just use an automotive grade for the upstream regulator (IC1) and an regular grade part for the downstream 5 V regulator (IC2)?

I'll try to add some details for clarity. I want to run a small 12 V device and was planning on running a current divider to the microchip so I don't run the device if I ever have less than 12 V.

The rough current requirements are as follows: - 12 V @ .833 A - 5 V @ .05 A - 3.3 V @ .15-.20 A

I was debating getting an automotive grade LDO and then using regular LDO's after that on the back end for the other devices.

This is a one off project currently but if it works I think I could build up a few and sell them down the road. So I'd rather do it correctly the first time and hopefully get a good design.

What is the device going to do? Where in the car - under the dash or bonnet? These determine the environmental conditions and thus the temperature range. If it will be required to run the car such as fuel injection, I would not skimp on the quality of the components. You will probably get away with normal regulators, but you would be sensible to add lots of decoupling and also an LC filter to keep transients and noise out. Paranoia may dictate a fuse and zener crowbar to protect against gross overvoltage, but this is probably overkill for a modern vehicle.

Feel free to post more info and I will give feedback.

Simon