Reducing Car 12VDC to 10VDC, I need help

Have a look at the supplies sold at

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. Chances are, one of them will do whatever it is you're trying to do. Their stuff works great.

-- jm

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Reply to
John Miles
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charging, then

alternator.

the

ago, is

You want a low dropout regulator. National fixed voltage LM2930, LM2940 and if you want adjustable, LM2941 will suit you just fine. GG

Reply to
Glenn Gundlach

Hi--- Is there an IC that is made for car battery voltage reduction, and is "stable" ? If I remember, a car system goes up to about 14.4 volts while charging, then down to about 13.8 VDC, plus has a terrible ripple due to the 3 phase winding setup from the ac/dc conversion by the diodes at the alternator.

I need a nice smooth 10 VDC at about 20 to 80 mils range. (Don't know the exact mills for sure yet)

I'm an old geezer that had an associate in Electronics many decades ago, is totally outdated, now. Any help would be greatly appreciated. Thanks in advance! :-)

Ron------

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Reply to
Ron G

I agree, 'mils' is used between engineers in conversation, so is 'mA'.

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Reply to
Luhan Monat

People do indeed say "mils" when speaking of mA. They =write= mA, but =say= "mils". It's pretty hard to get "mils - mA" mixed up with "mils - thousandths of an inch" in a discussion

Reply to
CF

What you want is readily achievable. The LM117 or LM317 can do it.

You might even be able to use the TL431. If you only need 20 mA, the TL431 might be a good choice. If you need more, the LMx17 might be a better choice.

Take a look at the datasheets for these parts and see if you think you need more help.

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Also, note that in general, people don't use "mils" as a measure of current. A "mil" is a thousandth of an inch. "Milliampere" is abbreviated "mA."

--Mac

Reply to
Mac

Before you do anyting automotive, read this.

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I'm not familiar with the numeric parameters associated with "nice smooth".

If you expect to get 10V out with ALL automotive conditions, you won't get there with a simple linear regulator, LDO or otherwise.

Whatever you do, make sure you have LOTS of transient protection on the input.

I always caution novice auto power supply designers to weigh the cost of the device they're powering against the money you save building your own supply. Risking a $2K laptop on a $20 savings in power supply design is false economy. YMMV.

There are also a bunch of other automotive considerations depending on what you're trying to do. For example, I've never achieved a power suppy for my mp3 player that didn't have excessive ignition and alternator whine sneaking thru ground loops.

mike

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Reply to
mike

It can go down lower than 13.8 V, if you're talking about when the engine's not running, or if the engine is running but there is a high electrical load. A fully-charged car battery at no load is about 12.6 V; you'll get less than that at the cigarette lighter socket and less still if someone is sitting there with the key off and the radio and dome light on, etc. During cranking, most cars go as low as 9.5 V or so at the battery and still start. I have heard a suggestion that when designing for automotive use, a device should "work" over a 10 V to 15 V range, and "survive" 0 V to something well over 15 V, like maybe 30 V or more.

I second the LM317 suggestion. That's a linear regulator that is good for at least 1 amp (in the TO-220 package) with a heat sink; you may not need a heat sink or only a very small one for your small demand. IIRC the maximum drop through it is about 1.3 V, so for your 10 V requirement, the input has to be at 11.3 V or more. If the input is less than that, you'll probably get whatever's at the input minus 1.3 V, unregulated. In other words, this device won't "work" down to 10 V, but that might not be important to you.

The other option is a DC-DC converter. This is a little brick that typically takes a wide range of DC input, chops it into AC, runs it through a transformer, rectifies the AC back into DC, and regulates it. This will be more expensive than the linear regulator, but will work over a wider range of input voltages. The other problem is that a

10 V output is hard to come by; you could use two 5 V converters and wire the outputs in series, or use a 12 V output one and follow it with a linear regulator. Basically, what this buys you is operation over a wider input voltage range, and a little more isolation from the car's electrical system.

Yeah... They changed which end of a soldering iron to pick up and everything. :)

Matt Roberds

Reply to
mroberds

on

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ES-XW7T-1A278-AB/C: Component/Subsystem EMC Requirements and Test Methods

Part 3 Figure CI 240 -1, Load Dump Test

martin

After the first death, there is no other. (Dylan Thomas)

Reply to
martin griffith

I have never heard anyone say "mil" when talking about milliamps. Could be lack of experience or exposure on my part.

In any event, I believe my comment still applies to written communication.

--Mac

Reply to
Mac

Which is why I pointed him at mini-box.com. Whatever your automotive power problem, it's safe to say that an LM317T is absolutely NOT the solution. :)

-- jm

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Reply to
John Miles

That would be something like the LM2941C, this is designed to withstand the automotive load dump as well as to provide other excellent performance characteristics, such as requiring a mere 100mV input-output differential at your low load levels. See

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and page 8. You will want to place a high voltage diode in series between VBATT and Vin to the regulator- most applications use 1000PIV- to guard against the occasional negative transient on the BATT line. Your regulator will dropout during extreme cranking load- but otherwise should work peachy keen in every other circumstance.

Reply to
Fred Bloggs

"It's volts that jolts, but it's mils that kills"

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Reply to
Fred Abse

mil = 202.25 arc-seconds, roughly.

Reply to
jtaylor

'thou' in British usage. "A book of verse, a flask of wine, and 25.4 micrometres" doesn't quite have the same ring to it.

Paul Burke

Reply to
Paul Burke

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