Automotive '12V' Power

LittleFuse has some good app notes, including 9312 (inherited from Harris), which gets cited a lot in these discussions.

Also, a saved posting from a few years back:

--8 "load dump" condition, where the supply can e.g. rise to ~125 volts

I just use 1N4007 to block -ve transients, a 3 ohm series resistor to limit the current during transients, a SA28A TVS to clamp the peaks,

-- Joe Legris

--8

LM317HV is spec'd for 60 volts in-to-out. You could make a homebrew regulator that was good for hundreds.

Google...

load dump protection circuit

John

... and don't build anything that goes *PHUT* at less than 60V. If you want it to survive.

Oh, and polarity protection, if it goes into a simple vehicle or if the user can muck with the wiring to this device. Because in the end most will whistle and say "I dunn nuthin'" when calling in their warranty claim ;-)

ST have a useful technical article, TA0338, on "Designing robust protection of automotive power rails against overvoltage and reverse polarity battery hazards."

That article starts out by referencing a handful of standards: ISO 7637, ISO 16750, ISO 10605, and SAE J-1113.

The graphs showing surge events detail why the automotive environment isn't for the faint of heart -- 87 Volt load dumps, +/- 100V spikes, reverse battery connection, 24 volt jump starts... You're going to need a little more than a 7805 to get past that!

A very useful article -- enjoy.

When I was in the 2-way radio business, an excavator co. was a big client. These were 100 watt 31 Mhz RCA radios. The ones in "tri-axle" dump-trucks ran tapped off the lower 12V battery; the vehicles were 24V.

One came back with the "helicopter" [ie stud mount with 4 'blade' tabs] RF transistors all rattling around loose inside; both drivers and output ones.

Seems they had jump-started the balky truck -- with a 200A Lincoln Electric DC arc welder.

On a sunny day (Tue, 28 Jun 2011 12:38:49 -0700) it happened John Larkin wrote in :

For higher currents you could use the LM2596 switcher. It can handle 40 V DC in, for many output voltages. Less heat than a linear regulator.

There's also the TL783, which is good to 125V with full SOA protection and thermal limiting. Its dropout voltage is the pits, though--about twice as bad as a 317.

Cheers

Phil Hobbs

I have used LM5574 quite a lot for this - wide range switcher:

Transient line regulation would be interesting in a load-dump situation. Switchers aren't usually spec'd for that.

John

DId I miss the post where you asked Tim to pull your finger?

You can ALWAYS count on John Larkin to "answer" with a totally useless generality. I haven't been able to figure out what mental disorder that represents... perhaps narcissism... the first paragraph of...

matches Larkin's behavior right down the line. ...Jim Thompson

SAE has the last word on this, you're mainly interested in conducted emissions immunity, the standards are pricey for a one-time buy.

It's hard to account for whatever you have missed.

Give us your suggestions for voltage regulator circuits suitable for automotive use.

John

But 40V ain't enough in a 12V automotive situation ... PHUT ... *POOF*

That's exactly the stuff one must reckon with, especially with vehicles used way out there. Another unorthodox method that is sometimes used to start a recalcitrant vehicle is to place two batteries in series. "Cuz it's gitten'em cranked over". And then there is the Siberian method: Gather some wood, pile that under the vehicle, light, smoke two maxorka cigarettes, try to start.

Motorola has/had an app note for their surge suppressing diodes that went into the hazards of automotive power.

Motorola hasn't been in that business for over a decade.