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Topic: External power supply dimensioning (Read 2581 times) previous topic - next topic


Hello! New to the boards, I hope this is the right place in the forum to ask...

I'm working on a project where I need to control a servo motor and dim 1-4 LED strips. The project is in it's early stages and I have not got the specifications of the LEDs or servo quite fixed. I'm thinking about how to power this best and if one power supply will do the trick.

The thing is I'm not so sure about what kind of maximum current one can assume a servo motor will drain. Does anyone have a clue? The servo I've been given for testing is a SuperTec S03, which I find it hard to find specifications for.

Furthermore I think the LEDs are likely to be run on 12V voltage. Is there a clever way to control them using the arduino PWM output, which seems to be capped at 5V if I'm getting the manual right? I'm thinking optocontrollers maybe, but I'd appreciate feedback.

Do you recon one Arduino powered with a 12V 1A DC powersupply would be sufficient, or will I have to set aside one board for the servo and one for the LEDs?

Sorry for the vague info and many questions. I'm hoping that you guys can put me in the right ballpark for what to expect...



I think the easiest way to do this is to use an TLC5940 which will drive LED's up to 18v. Use one power supply and split it between the Arduino and the TLC5940. You then get an extra 16 PWM outputs too. They only cost a few USD.


don't know what board you are using, but I built mine with an 7805 voltage regulator and it is running a standard size servo just fine. Though, a servo with a full load can draw up to 2A, but since it is just for short time, it's not a problem. If not sure, just use another 7805 just to power a servo.
For driving led's you could just use a simple transistor circuit...


Dec 30, 2008, 02:20 am Last Edit: Dec 30, 2008, 02:22 am by maestrovik Reason: 1
Mike Mc - I looked at the TLC5940, and it looks like a good solution. Thanks for the tip! I see that you're English, and presuming that you still live in the country, do you have any tip of a supplier in the UK?

Odisej - My board has a 1117-50CE voltage regulator which is speced to 5.0V; 800mA. Can you explain why you say "but since it is only for a short time, it's not a problem"?

Is it possible to do this this on one board? I looked at an LED strip from Maplin (Still don't know the one I'll use for real, looking around for reference) where each strip pulls 250mA. I'm starting to think I'll need one board for controlling the servo and one for the LEDs each board powered by it's own pover supply or I'll be trying to pull to many A. Or am I getting the wrong end of the stick somehow?

Thanks for your valuable input guys!


Well... my statement goes to cooling the power chip. If I would want to drive 1A of current all the time, I would need to install a heatsink. But since a servo only takes a short time to turn (and within that time it consumes most of the power), I did not need to  instal a heatsink to my 7805.

With a 800mA regulator I can't say what will happen. Depending on your load on servo! If for example you will just use it to lift a few grams, if should be ok, but if you will move a large object around, I would recomend building a separate power suply with LM7805 that has a peak current at 2.2A. Here you go, a datasheet.


You won't need two Arduino boards, but you will probably need a bigger, external, power supply and regulator.  The usual choice of regulator chip is the 7805, but there are others with higher ratings.  Maplin's have the 78S05, which is rated at 2A, for instance. If the power drain is continuous, you will need a heatsink.

As for suppliers, I get a lot of stuff from Farnell (uk.farnell.com), but other suppliers are Rapid Electronics, Active Robots and for the not-so-electronic stuff, MUTR (www.mutr.co.uk).  Farnell are a trade supplier, but you can pay with a credit card over the web, although there is a certain minimum order value (20 quid I think).


Thank you so much for your help! The design has moved on and it seems the LEDs will be controlled in another fashion, and I am only left with powering and controlling the servos.


Hi all,

Mind if I join in?

When you talk about separate supply and servos and motors, do you mean a separate power source, ie two batteries, or will one source like a big 12V battery directly and via a voltage regulator do? When a large consumer is draining from the battery, will the voltage drop in the regulated circuit?



How would you go about using an 18VDC power supply (to power 4 LEDs in series and be under the limit of the TLC5940), but, provide the Arduino only 12VDC from that same 18VDC power supply since it's apparently only advisable to use a max of 12VDC to power an Arduino?


but, provide the Arduino only 12VDC from that same 18VDC power supply since

Just use a 12V regulator. Like the 7812.


I wondered if it was as easy as that.... awesome, thanks!


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