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Automobile Electrical Parts Requirement

liuyalan1204 liuyalan1204
New User | Posts: 1 | Joined: 11/17
Posted: 11/22/17
11:28 PM

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 Digikey: 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:

11 23

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.  

Just Try It1 Just Try It1
Moderator | Posts: 2796 | Joined: 08/14
Posted: 11/23/17
08:30 AM

i don't have an exact answer for you .. i am trying to think what you might need totally clean power for in a car..

you might ask here..

there is a science to building power supplies that are quiet. and it takes some tools to verify they are quiet.  at least a digital scope.. and some dummy loads of different values.

my brother (RIP) spent his life getting rid of humm and hiss from recording studio equipment to prevent it from getting into the music you may enjoy..  he was never happy till he could turn the master volumne control all the way up with all the equipment patched in and turned on and get NO Hum or hiss from the speakers..  and he always verified it again via play back from the 24 track tape studer A800 and A820 tape recorders.   he went as far as using teflon insulated 8 gauge wire for the speakers.. using a drill to put a twist in the pairs and using exactly the same length wires for all the speakers..  plus all the same length wires from the console output to the amps..  mods to the amplifiers to get rid of hiss also.

he actually had an expensive piece of test gear from Sound Technology. it put out precision tones and measured the distortion coming back into the unit.

there was one custom made recording console.. that had been uses for many many years to record many rock and roll albums. it had a hum and hiss at higher frequency that did get into the recordings.. during recapping the console.. it took $11 dollars of resistors across 48 channels to quiet the feedback that had plagued this console for decades.  the guys who owned it were crazy happy.. it even got in MIX magazine..  

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