How to drive 400W of High-Powered LED's in parallel / series?

I want to create a luminaire (a lighting unit) comprised of the following:

• 5 Nichia LEDs running @ 70.2W / 39V / 1.8A
• 6 Cree LEDs running @ 2.2W / 3.2V / 700mA
• 14 Cree LEDs running @ 1.61W / 2.3V / 700mA

I have included two schematics, the first separating the luminaire into 6 circuits:

• The 20 Crees running on 1 circuit
• The 5 Nichias running on separate circuits.

The second circuit groups the 20 Crees with 1 Nichia, and then 2 Nichias per circuit.

I want to drive the circuits using a DC to DC 10-32V to 10-46V 150W Boost constant current power supply Regulator like the one found here:

My questions are these:

• Does my first schematic work? And does my second schematic work?
• What kind of consideration should I take in running the two Nichia LEDs in parallel if any?
• Is the DC - DC Driver stable enough since it is constant current?
• Any other suggestions to make it more stable? (When using only 3 drivers as opposed to 6)?

Finally, does anyone have any idea how to maybe run this rig more efficient? I mean, how can I create this same light with only 2 circuits?

• Circuit A: Run the 20 Cree LEDs @ 700mA - 39W
• Circuit B: Run the 5 Nichia LEDs @ 1.8M - 351W

Does anyone know of drivers or chips that can handle that much power? 350 Watts? And is the choice of my PSU ok? It will be either 24V/16.7A/400W or 12V/33.3A/400W.

• That's a lot of questions, with very narrow utility. Sounds like you should hire a professional engineer. – Phil Frost Jan 7 '14 at 14:49
• The second schematic has a bad idea in that it's running two large LEDs in parallel; the current is not guaranteed to balance between them! I'm not sure where your "stability" concerns come from? You could run all the Nichias in series if you could find a suitable 200V driver and you're not going to encounter regulatory/safety problems. Is this a product or a one-off? – pjc50 Jan 7 '14 at 15:48
• Driving two leds in parallel without a resistor that can balance the currents is definitely a bad idea. No two leds are completely identical and as temperature rises Vf lowers so things get even worse. – alexan_e Jan 7 '14 at 15:54
• Hi PJC. This is a one off build for personal use. It does not need to "pass" regulatory, although I still want it to not burn the LEDs and set fire to the house. This is a prototype. I just can't seem to find ready built high voltage high power Drivers. I mean, I would need 200V in series @ 350 Watts. If you have any idea of an IC or schematic of achieving this that I can look at. I just can't seem to find info on powering BIG LEDs. Everyone has schematics for so called High-powered 3W-12W. – fizzy drink Jan 7 '14 at 15:55
• @pjc50 Hi PJC. This is a one off build for personal use. It does not need to "pass" regulatory, although I still want it to not burn the LEDs and set fire to the house. This is a prototype. I just can't seem to find ready built high voltage high power Drivers. I mean, I would need 200V in series @ 350 Watts. If you have any idea of an IC or schematic of achieving this that I can look at. I just can't seem to find info on powering BIG LEDs. Everyone has schematics for so called High-powered 3W-12W. – fizzy drink Jan 7 '14 at 16:52

1 Answer

There are many drivers. Not so many that will power 20 in a string. Many you can expand the voltage to what ever by using an extra MOSFET.

The 14 Cree must be Red probably XPE wich are typical 2.4 at 700mA. I have found XPE to be about just under 2.0 Volts at 500mA.

You will need massive thermal management to run them at 700mA.

20 is pushing it. I went with 16 max but that is for all colors. 20 Red would squeak by. To be compliant with Electrical Saftey I keep voltages at 48 max.

You approach depends on how any you are going to make. Is it a 1-2 or are you going into production?

Running LEDs in parallel is not acceptable to me. There are those that can argue that point but they would be wrong. Been there done that. It will work only if the LEDs are running at ambient temperatures which is not the case here.

I just got in a TI Eval Board for the LM3466 load balancing circuit. It appears to be the way to go with parallel strings when the current is constant and they are not dimmed.

You can build a very efficient DC-DC driver for $2-3. I would power your circuit with more than 12V for efficiency and cost. A boost driver will cost more than a buck step down driver and be a little less efficient unless you spend more. I'm not a big fan of COB arrays. Too much heat in too small an area. You will need very good thermal management to pump them at 70 Watts. Chilled liquid cooling would do it. If you are just making one or two use constant current poser supplies. The Meanwell HLG series would do very well here. One supply for each string unless you use a load balancer for multiple strings. 40 @$30, 100W @ \$47.