Automotive Power Supply

[logictom]

I am looking to power a circuit from either 12 or 24v vehicle battery system and I am curious to see what other people have implemented or recommend in terms of power supply for electronics.
I will be using a microcontroller along with some other ICs, mix of 5v and 3.3v.
I was going to use a zener to cap spikes followed by a switching supply to bring the supply down and then use a LDO regulator for the 5 and 3.3v individually. I was also going to fit some zeners to any i/o in case of any spikes creeping through that way.
If anyone has any links to app notes they have found useful I would appreciate a link or two

[Baliszoft]

How much current do you need? If not much, you can for example use a higher wattage (f.eg 2-5W) low value series resistor (f.eg 10-20Ohm) followed by a (schottky) rectifier diode (200V blocking capability) (for reverse battery protection) and a transient voltage supressor (24V f.eg on 12V systems), buffer cap, (100nF), an automotive LDO (i am using TLE4266 f.eg), .... + optional 5V TVS. This works without problems for me in the automotive environment. If high currents are needed, you have to omit the series resistor and go thougher with the TVS diode. F.eg Vishay SM8S series. They ain't cheap.

Would be nice to hear what others use.

EDIT: http://www.vishay.com/docs/88490/tvs.pdf

[ptricks]

Here is a link to a pdf about all kinds of automotive supplies.

http://www.powersystemsdesign.com/library/resources/documents/north_america/2010/psdna_julyaug10.pdf

[richcj10]

Here is what I use for robotics. I try to power everything off of one battery to conserve weight.
It works well. But, there is always room for improvement!

C23 is a 5kv rated cap.

[TheDirty]

I use an LM2940 or LM2937 reg with TVS for smaller loads, but I've had to go to switchers for some bigger loads.

LM2940 and LM2937 are automotive spec with reverse voltage protecting, surge, and thermal protection built in.

[george graves]

^awesome.  Do you have a part number or spec for the TVS that you'd recommend?

[Baliszoft]

I use an LM2940 or LM2937 reg with TVS for smaller loads, but I've had to go to switchers for some bigger loads.

LM2940 and LM2937 are automotive spec with reverse voltage protecting, surge, and thermal protection built in.

I have used the lm2940 in one of my older projects, but i prefer infineon's/ti's tle42xx ones. I found that the 2940 has got worser tolerances regarding to output votage and load regulation. The 5v batch (all pieces) i was working with was delivering only ~4.89v with 150mA load, while the tle42xx-s were a lot more closer to 5V. Lm2940 has got a built in load dump protection, which turns off the output in such a situation, which may not be a desirable effect in all designs.

If you dont use a separate reverse protection diode, then you have to go with a bidirectional tvs otherwise the tvs may fry when powering in the reverse direction. Of course there should be a fuse (some actual designs rely on blowing a fuse when reverse connected).

[logictom]

Thank you for all the replies, I will have a look at each of these to see what fits best.
I am still designing the rest of the circuit so will wait until I know my current requirements and if any other voltage rails sneak into the design

[george graves]

ea...you know I do do that...I do run e into me..

[george graves]

I came...