Regulated power for electronics in a car

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Captain Dondo 20 years ago

(I posted this to s.e.b. a couple of days ago and received no replies... If you follow both groups, apologies...)

I am about to install some consumer electronics gear in a car. One piece runs on 12VDC the other on 5VDC.

I know just enough about car electrical systems to be dangerous, but....

I figure that the 13.8 VDC in a car is pretty dirty, and probably not really stable, so I want to use some voltage regulators and filters.

The filters I actually have - they're just basic cheap coil/cap type stuff.

I'm thinking about the regulators... Since I don't need much current, I figure I can use something like a L4940V12 and a L4940V5 - both of which are self-contained 12VDC and 5DV regulators. More info on them here:

I figure I can scrounge a heatsink from an old CPU for a few bucks...

I have two questions:

Are these likely to be effective? And, just how much external circuitry do I have to have to make these work in a minimal way? The spec sheet just shows two caps. Will this be enough?

I plan to connect these to my filtered DC, so the worst of the ignition noise should be gone.

But do I need a zener to ground as well? Any suggestions?

Thanks,

--Yan

o__ ,>/\'_ o__ (_)\\(_) ,>/\'_ o__ Yan Seiner, PE (_)\\(_) ,>/\'_ o__ Certified Personal Trainer (_)\\(_) ,>/\'_ o__ Licensed Professional Engineer (_)\\(_) ,>/\'_ Who says engineers have to be pencil necked geeks? (_)\\(_)

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bill.sloman 20 years ago

Don't use these parts - they seems to have a maximum input voltage limit arround 17V, which isn't anywhere near high enough to survive in a car, where the 13.8V can spike up to 60V.

See if you can find a pair of regulators rated for automative use.

ON-Semiconductor has a selector guide that shows what you might be looking for in the way fo transient over-voltage ratings

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Linear Technology's web-site offers the LT3010, which looks to be exactly what you want - if you can actually buy it. Farnell don't stock it, which is a bad sign, though Arrow seems to. It is an adjustable three-terminal regulator - like the LM317 - so you need two resistors to set the output voltage you need. You could buy the LT3010-5 for the

5V output, but there doesn't seem to be an LT3010-12.

Bill Sloman, Nijmegen

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Captain Dondo 20 years ago

Thanks!

Fishing around based on your comments, I found this:

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It sounds like it will work... If I read it right, it should work with 13.8 V in, no? Comments?

And it's still only < $3 - and I only need one part, not two....

--Yan

o__ ,>/\'_ o__ (_)\\(_) ,>/\'_ o__ Yan Seiner, PE (_)\\(_) ,>/\'_ o__ Certified Personal Trainer (_)\\(_) ,>/\'_ o__ Licensed Professional Engineer (_)\\(_) ,>/\'_ Who says engineers have to be pencil necked geeks? (_)\\(_)

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bill.sloman 20 years ago

I've had a quick look a the data sheet at

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and it does seem to be pretty much what you were asking for.

Bill Sloman, Nijmegen

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Ron G 20 years ago

I

which

Hi--- Is there any other circuit that would give me clean 10VDC at maybe 25 to 100 milliamps, for car use? Thanks allot for your help--- Ron in Illinois (used to be in electronics many decades ago--now outdated :-(

NewsGuy.Com 30Gb $9.95 Carry Forward and On Demand Bandwidth

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Stanislaw Flatto 20 years ago

Hi! If memory serves power zeners were introduced in the last few scores of years of last millenium.

Have fun

Stanislaw '63 graduate electronics

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Ken Smith 20 years ago

In article , Ron G wrote: [...]

I assume that you don't need the 10VDC to remain that high during a "cold crank". If so, there are quite a few circuits that will work for you.

Just for fun, I'm going to sketch one out in ASCII art and see how the nice folks here react:

1N400X PTC DN3525 Vbat--->|-----/\\/\\-----+---------- -----Vout ! d! ! !s Vout --- ----- ---------- --- ! ! ! !GND \\ \\ \\ / / / --!!--/\\/\\-- \\ \\ \\ ! ! ! / / ! Vout ! ! ! ! ! ! ! ! +------ ! ---+--!-\\ ! ! ! ! ! >------+--- ! +-------!+/ \\ ! ! / /---/ GND \\ ^ / ! ! ! GND GND

Important points:

The depletion mode MOSFET means that the gate voltage doesn't need to be above the available voltages.

The OP-AMP gets run from the regulated output.

So far, there is no current limiting.

So far, there is nothing preventing "wind up" in the servo loop.

-- kensmith@rahul.net forging knowledge

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Stanislaw Flatto 20 years ago

Vbat---->|--->|--->|----+---Vout | --- --- Vbat 13.7 - ~12V. Vf (1N400X) ~0.7 - 1.1v. So three or four diodes in series will give the voltage drop almost unaffected by current range (within reason).

Stanislaw Slack user from Ulladulla.

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Regulated power for electronics in a car

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