Advice on power scheme for 5 3w RGB LEDs

I need to drive 5 3w RGB LEDs where each color eats about 350ma (I will likely drive them at ~200)
I have 15 little 320ma constant current drivers that will take AC or DC < 20v. I can swap out the resistors on the CCDs to lower to 200ma. They are based on the PowTech PT4115, which has a pin for PWM control at +5v.

The RGB emitters will be in 5 separate locations approximately 50cm apart.

My options as I understand them:

  1. I can build a nice actively cooled enclosure to hold all 15 drivers, the power supply and my arduino mega which will control all the PWM for the drivers.
  • nice thick bundled wire sets to go to each emitter, leaving each emitter pretty easy to place without a lot of bulk - it will leave more room for the heat sinks :slight_smile:
    -I can have the power supply pop out AC or DC. I can’t think of advantages of either except perhaps that if I use DC, I can remove the bridge rectifiers on the CCDs and perhaps gain some efficiency?
  1. One enclosure for the power supply and arduino with power AND data wires (eeep! 5vdc and AC running in a wire bundle together? If I do it like this, perhaps I use DC supply power.
    -I can have a board in place with 3 CCDs and the emitter. Seems like a lot of heat in one place that would be more challenging to cool - while at the same time, it’s not FIFTEEN of them in one case as in the first idea…

I am open to any ideas anyone has and appreciate your time in advance!


I also just had a bit of a HRM about power supply voltage. Aside from the fact that It will need to supply 8a (very unlikely, but going on max values…), it will also need to be able to feed all of these constant current drivers. As I understand it, they will suck up as much voltage as necessary in order to provide the current they are set to. With fluctuating requirements like that, perhaps going with one AC supply for those and another regulated supply for the arduino might be best?

edit: added the bit about supply voltage

It was a bit hard to follow. What I understand is you want to control every RGB LED seperately, otherwise it does not make sense to have 15 drivers. How you are going to have 15 PWMs from a Arduino ?. If you need to have high dimming ratio, you may need to change the PWM frequency. take a look at http://arduino.cc/forum/index.php/topic,51887.msg390972.html#msg390972. LED driver should not dissipate much heat at 200-350ma. I don’t think location of LED driver is going to be a problem.

Thanks for your reply. With two of the emitters, I'll likely leave one color unused. This means I'll only need to have 13 PWM pins. The Mega I mentioned in my first post has 14.

I am also looking at the Cat4109 chip which will overcurrent to 200ma. That should give me enough brightness for my purposes and has the advantage of switching VERY fast, alleviating some of the issues in the post you cited. At $2.20 a chip, it will be cheap to build on. Just have to heatsink them :)

Running them in parallel like this means I'll want to get a ~12v dc supply capable of supplying around 5a which is no problem.

Still not quite clear. When you power 5 x 3W LED = 15W, why do you need 12V x 5A = 60W power ? If you use switching driver you mentioned, you just supply whatever voltage that the driver support. Switching driver normally have >75% effciency. 1.5A> at 12V would be OK. If you use linear LED driver like CAT4109, you want to have as close as possible to LED Vf to reduce power dissipation and increase efficiency. >3A at 5V should be good for the linear driver.

I felt I was being conservative. Assuming full drive at 200ma, we'd have 3A draw. Powering the arduino and any other bits that might end up in the case means a bit of headroom would be nice. I can see that you're right though about the excess voltage into the driver circuit. I'll plan on 5v/3.5A or so.

Thank you for your help! I'm a programmer moving into electronics, and I miss the point sometimes!