Proper drive & control for high power RGB LED's

Hi all,

I know I'm not the first one asking this around here, but in 2 weeks of scouring the internet I have still not found a satisfactory solution to control my DealExtreme common-anode RGB LED's (star shaped).

The regular solution of throwing some power resistors at the problem is something I wish to avoid. The current these things draw will cause a lot of unnecessary power usage and heat development.

What then opens itself up is a wide world of constant current style controllers, but I can no longer see the trees through the forest.

My wishes are simple: -I need to sink(!) about 250 mA per colour (common anode design). -I want to be able to PWM all channels, otherwise whats the point of RGB. -I would like to keep component count as low as possible. -Preferably no linear solutions due to heat development, but I can live with this if need be.

Is there anything that fits the bill without braking the bank? (Yes I have seen those 20$ buckpuck IC's, but I'd need 3 per LED, not an option).

I would really value any opinion. Thanks in advance.

Well one forum member here is working on an interesting LED driver shield for the Arduino community. Why don't you read the postings and see if it's something you might be able to utilize. Not sure if it's shipping yet, but check it out for latest update.

http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1258412419

Lefty

This problem is something I have been working on slowly the past month as well. The power LED shield linked to above looks great except for the cost for all the components is a little high for me. Seems to be around $90. Most of that cost is associated with the Luxdrives (Buck Pucks) @$15 each.

The only other solutions I have found for cost effective constant current circuits are linear. Where a MOSFET or voltage regulator are used as variable resistors. The MOSFET versions I have found are much more efficient than the voltage regulators.

Thanks for the replies. As you point out, the cost when using buckpuck style regulators escalates pretty rapidly, which is a shame. What I cant figure out is why I cant find any commercial driver IC for this type of LED. They are being produced, so you'd expect one of the big semiconductor manufacturers to have come up with a driver solution. All I can find that comes close can only regulate the drive current though.

My knowledge of electronics has waned quite a bit since my days at the faculty, but using Mosfets as variable resistors sounds better than the old big ceramic resistors. All I know from the old days about mosfets is to fear them... Very sensitive to static electricity, and I have heard them go POP in heatcycle testing in a PCB assembly factory I used to work for.

An option that strikes me as interesting is using the drivers found on the driver pcb's DealExtreme is selling for Cree style white light LED's. I cant remember the exact component type, but it's supposedly a linear regulator that can be PWM'ed (although it is not designed to). From what I understand they do get very hot in use.

Finally found something that looks like it will work:

The ST STCS1...http://www.st.com/stonline/products/literature/ds/13415/stcs1.htm

Acts as a current sink, allowing for direct connection to a power source between 4 and 40 Volts, and can drive up to 1500 mA.

The price is nice too at $2.55 when bought per 10. Now I just need to find a supplier that doesnt charge $30 for shipping like Digi-KEy does.

Any other people interested (near the Netherlands)?