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skinnermk
11-05-2010, 04:48 PM
What is the best way to take 12V DC from a battery down to the 6 to 9V that the proto boards require? Is the proto board not capable of 12V? It looked to me like the regulators and caps are the same I use to drop 12V to 5V in a standalone implementation. Any information is appreciated. Did a ton of soldering and don't want to chance ruining a board for a test.

Thanks in advance,
Mark

max72
11-05-2010, 05:28 PM
Problem is heat dissipation.
12V coud be OK is you current is not too high. I used this solution in the past, but it was ok as long as my LCD had the back light off.

check also this discussion:

http://forums.parallax.com/showthread.php?t=126774

Massimo

Loopy Byteloose
11-05-2010, 05:47 PM
I'd have to say there are a lot of good ways, but no really best way.

Why so? The most energy efficient take more parts and are more costly. While the minimal part counts and minimal cost (like a 7809) will waste up to 30% of your power in heat.

There certainly are some bad or not so good ways, like a simple voltage divider with larger wattage power resistors. It runs very hot and wastes even more energy.

The problem with the existing on-board regulator is that it is surface mounted without an additional heat sink. IT will tolerate 12volts without internal damage, but if you really use all its output capacity it might get so hot as to melt the solder and slid off the board.

Leon
11-05-2010, 06:07 PM
It should go into thermal shutdown before that happens.

Rayman
11-05-2010, 06:39 PM
I think the best way would be to use a switching regulator like the LM2596...

Any easy and cheap way is to one of those cigarette lighter to USB adapters and then use a USB to power cable straight into your proto board...

skinnermk
11-05-2010, 08:31 PM
I was looking at the adapters. This isn't for a vehicle, but for a robotic platform. I'm using a separate regulator to drive most of the devices so this is mainly for the prop and IO pins only. I looked at the thread mentioned and there were a ton of options given, but I never saw a schematic for any of the solutions.

It sounds like if it was only the prop and not much draw from devices the on board would work. Do you agree? I don't have to worry about starters and dropouts so the on board seems to be acceptable.

If someone has a schematic or a reference to one I'd appreciate it.

Thanks,
Mark

Phil Pilgrim (PhiPi)
11-05-2010, 08:52 PM
You could just buy a DC-DC converter:

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=296-20110-ND

-Phil

Rayman
11-05-2010, 10:52 PM
I bet that part Phil found is also using something like a LM2596.

Here's my circuit to do 12V to 5V conversion...

max72
11-05-2010, 11:29 PM
If you have little load on the protoboard you can have a go as it is.

The suggested solutions use a regulator (linear or switching) in an out of the box configuration. So if you check the datasheet of the suggested part you'll find the schematic with components values, or, when critical, even a manufacturer's part number.
For instance go to national.com and search "2596".

Massimo

laser-vector
11-05-2010, 11:45 PM
ive never had a problem with the professional board, like max said the load my cause an issue, but the vregs will shutdown before any damage.

best of luck!

Loopy Byteloose
11-06-2010, 01:10 PM
If it is just the Prop that is in use via existing regulation on the board and you want to drive it at 12VDC, why not just put in a 500 ma fuse to be on the safe side. If that blows, move up to 750ma. At least you would have some protection and an indicator of how much your current draw is.

The mouse and keyboard are really power gluttons - each nearly draws 500ma at 5 volts and that pretty much dictated the design of the voltage regulation. If you aren't using either, a whole bunch of assumptions change.

But also be advised that in an automotive environment, 12VDC is a bit of a deception - the battery charges at 13.8VDC, has peaks of 14.5VDC on a normal alternator regulator, and occasional 60V spikes and transients due to relay coils and switches. So the voltage regulator would likely need spike protection - like an MOV or some fancy zener diodes - and heat dissipation of the regulator would be assuming 14.5DC input, nor 12VDC. Suddenly, a switcher solution becomes more attractive if the switch can isolate all those conditions.

w4fej
11-06-2010, 06:24 PM
You could just buy a DC-DC converter:

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=296-20110-ND

-Phil

God I love this forum! :idea: Thanks Phil for that link. I had the same issues with 12vdc to 8 and 5 VDC. My sub controller will be powered either from a 12VDC (13.8vdc) battery (sealed lead acid "plastic") or from a 12 vdc (13.8vdc) power supply while debugging etc...

Mike B.

Pyrotom
11-06-2010, 10:42 PM
I think it was Mike Green who pointed out this neat little adjustable voltage regulator....

<http://www.dimensionengineering.com/DE-SWADJ.htm>

skinnermk
11-07-2010, 08:01 PM
Thanks everyone for the assistance. I have done some testing and with my very low load on the on-board regulator I should be fine. Not in a vehicle so I won't have the voltage changes and spike that come with the electrical components in a car.

You all are awesome.
Thanks,
Mark

Peter KG6LSE
11-07-2010, 08:14 PM
those dimension engineering regs are amazing . just a tad on the pricy side . but for what you are doing there allmost ideal.

Electronegativity
11-08-2010, 03:10 AM
The absolute maximum input rating of those regulators are 30.3, and 32 volts, and they are designed for normal operation with an 18V input.

I would just plug it in.
They will get a bit hot if you are pulling upwards of an amp, but you are well within spec.

Here is the data sheet: http://www.national.com/ds/LM/LM1086.pdf

Q*bert
11-08-2010, 01:09 PM
I just finished building an adjustable step down regulator using an LM2576 and it works great. I really needed the voltage adjustment and 3 amps I could get out of this.

But, I just found the following 12V-24V to 7.5V "adapters" on Sparkfun and they are really good deals:

7.5V 1A @ $2.50 http://www.sparkfun.com/commerce/product_info.php?products_id=8835
7.5V 3A @ $9.95 http://www.sparkfun.com/commerce/product_info.php?products_id=9382

They even have the right size barrel plugs for Parallax boards.

Rayman
11-09-2010, 05:25 PM
Was just browsing Mouser.com and saw some new, very low cost and small 12V to 3.3 or 5V converters:

http://www.mouser.com/Search/Refine.aspx?Keyword=132637885%20%20

max72
11-09-2010, 05:47 PM
Pity minimum voltage is 7 volts, for a 3.3V output... could have been a great NiMh companion.

Phil Pilgrim (PhiPi)
11-09-2010, 05:59 PM
Rayman, great find! That's an astonishingly low price for a device with >5:1 input voltage range and low output ripple.

-Phil