Protoboad power supply

matb

I would like to run my protoboard in a car, so a max of 18V for a power supply, I am not using any extra periphials, so it really only needs the low current needed to power the Prop. Looking at the circuit and Nat Semi LM1086 specs it looks like it should not be a problem.

So I'd just like to confirm that is correct reasoning and de-rating to 6-9V 1.5A was for regulator heat sinking when running hight loads and/or the servo's?

At least at 12V I can afford a reverse polarity protection diode!

Paul Baker

Yes 18V is the upper limit of what the regulator can handle. You have to do some extra measures because the voltage in automotive is very noisy and cause issues with resetting the elctronics, if this is the case condtioning of the power is required. One user found that the programming header acted as an antenna and reset the Propeller until he placed a metal shield around it.

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Paul Baker
Propeller Applications Engineer

Parallax, Inc.

sharpie

I have found the National Semiconductor LM2825N series to be excellent power supplies... the -3.3 works great on the prop and can handle up to 40volts input.
And they all put out up to 1amp out.. Works great for most projects.. I should also mention they are not just regulators... they are switching power supplies stuffed into a small 24pin IC.

Oh, and the best part is you can get free samples from the national website!

M. K. Borri

You could cascade linear regulators (mostly to spread the heat output), keeping a reasonably beefy bypass capacitor between each stage is generally a good idea. If I need to run a 5V gizmo off my car, I generally have a 7812 -- cap -- 7805 -- cap -- load. Not very pretty electronically but it works. So in this case, you'd want to get yourself a 7812 (5A large casing would be a favorite) which will give you about 10.4 volts off a nominal 12 because these things aren't low dropout, and acts as a glorified fuse for when you get a voltage spike out of the car for whtever reason. Then you can run the board off that. If all you have access to is a radio shack, 7812's and 7805's can be parallelized, sort of... I strongly suggest you mechanically/thermally link the ground terminals on the heatsinks together by means of a screw and some nuts, and that you multiply current requirements by two (e.g. if you need to move 2 amps, buy 4 one-amp 7812's). Again, this is a bit of a redneck solution, but it WILL work.

If you want to spend a bit more money, look into these:

www.dimensionengineering.com/DE-SW033.htm
www.dimensionengineering.com/DE-SW050.htm

(Do throw in bypass caps anyway, even if it says they're not necessary -- it almost never hurts, and a cap grab bag is cheap)

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http://forums.parallax.com/showthread.php?p=650217

meow, i have my own topic now? (sorta)

Post Edited (M. K. Borri) : 5/20/2007 10:29:47 AM GMT