How to drive 400W of High-Powered LED's in parallel / series? - Page 1
Forum section: electronics / projects

author: made2hack
author_rank: Frequent Contributor
timestamp: January 07, 2014, 06:44:04 pm
content: Hello All!I want to create a luminaire (a lighting unit) comprised of the following:5 Nichia LEDs running @ 70.2W / 39V / 1.8A6 Cree LEDs running @ 2.2W / 3.2V / 700mA14 Cree LEDs running @ 1.61W / 2.3V / 700mAI have included two schematics, the first separating the luminaire into 6 circuits:The 20 Crees running on 1 circuitThe 5 Nichias running on separate circuits.The second circuit groups the 20 Crees with 1 Nichia, and then 2 Nichias per circuit.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:http://bit.ly/KzHhID(eBay Link)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 - 39WCircuit B: Run the 5 Nichia LEDs @ 1.8M - 351WDoes 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.UpdateI have received some comments on another board such that maybe I should use a ixysic driver such ashttp://www.ixysic.com/Products/LEDDrivers.htmor something from onSemiconductor such ashttp://www.onsemi.com/PowerSolutions/product.do?id=LV5012MD. However, these mention in their schematic creating the entire bit all the way back to the AC Mains (such as I would create my own PSU). I don't want to deal with AC Mains, I want to live! I have no experience in AC and don't want to start.Should I create something to drive all 5 nichias in series? Or just have 5 circuits, one per Nichia using more conventional DC boosters, such as ones from 12V to 40V ??

author: con-f-use
author_rank: Unknown
timestamp: January 07, 2014, 07:38:17 pm
content: The boost converters are very wasteful. Also how long do you plan to make the 12V rail at that current and how thick a wire do you plan to use? What's the mains voltage in your country? Do you have big heat sinks for your LEDs? Also please link their data sheets for convenience. Btw: Only wimps are afraid of mains, men have a healthy respect and are simply cautious.

author: made2hack
author_rank: Frequent Contributor
timestamp: January 07, 2014, 08:00:16 pm
content: Hi,Thanks for the reply. Mains is 220/230 VAC (EU). It's not that I don't respect it, it's more that I have zero experience with mains AC power.The heat sink is 450mm Long, 190mm wide, 50mm high, plus the 4 fans that I am considering (Sunon 92x92x25) are the high output 65CFM (110m3/hr) version. However, I would like to use the "quiet" series which are same size, but run only @ 1440 RPM for approx 25CFM (43m3/hr).Do you want the datasheet for the LEDs? Or for the boost converters? Or for the potential IC drivers from onSemi ?

author: jmole
author_rank: Regular Contributor
timestamp: January 07, 2014, 10:06:14 pm
content: Quote from: con-f-use on January 07, 2014, 07:38:17 pmBoost converters are not inherently wasteful, they can actually be quite efficient. It's wasteful in this scenario because of the 12V supply requirement.You probably want a 48V supply, given your requirements.Checkout TI'sWEBenchtool, it will automatically configure LED driver circuits and power supplies, according to your needs.

author: Jon86
author_rank: Frequent Contributor
timestamp: January 07, 2014, 10:11:35 pm
content: Quote from: trs80 on January 07, 2014, 08:00:16 pmUnless you're an idiot (which I doubt), you'll be fine with mains AC. Just don't work on things whilst they're on, and don't do anything stupid!

author: jmole
author_rank: Regular Contributor
timestamp: January 07, 2014, 10:17:56 pm
content: Quote from: Jon86 on January 07, 2014, 10:11:35 pmUnless your an expert in building AC/DC power supplies at high efficiency, buy one off the shelf.You can get a lot of watts from a relatively cheap ATX power supply, if you're worried about the budget, or you can spring for a Mean Well or other industrial supply from Mouser or Digikey if you've got the cash.

author: Jon86
author_rank: Frequent Contributor
timestamp: January 07, 2014, 10:36:48 pm
content: Quote from: jmole on January 07, 2014, 10:17:56 pmVery true, but at the same time it can be good experience to have a go at building high power supplies, even if they aren't the highest efficiency.

author: made2hack
author_rank: Frequent Contributor
timestamp: January 08, 2014, 02:54:07 pm
content: I don't mind getting one from Meanwell, they seem quite popular.I would rather, at this moment, just get a reliable AC to DC power supply unit and just worry about the DC portion of the build.So, if I get a 48V PSU, (actually, I don't think I can go higher than 32V because the boost takes 10 - 32VDC In), the boost converter would be more efficient?I don't necessarily mind going with Option 2 (in my circuit design), but how can I "safeguard" the leds in parallel? I mean, I am sending 3.6A from the boost, but no other safeguard in between. Is there an easy method?

author: richard.cs
author_rank: Super Contributor
timestamp: January 08, 2014, 03:09:53 pm
content: Some initial thoughts:Circuit A would work.Circuit B is likely to run into problems with current sharing between parallel LEDs, if you want to reduce the number of drivers put the LEDs in series.If these are fans with brushless DC motors (such as common PC fans) be careful putting them in series, they may not work properly. They include electronics to control the commutation of the motors and this might not like the high voltages that appear if the motors are not equaly loaded or identical. As a minimum I would shunt the fans with sizable capacitors because the current drawn by the motors varies thoughout their rotation.Efficiency will improve if you can avoid the multiple voltage transformations. I personally would put all of the Nichia LED arrays in series and use a 1.8A 200V current source powered from 340V d.c. rectified mains. I would suspect there is off-the-shelf equipment that could do this, as well as LED drivers I'd suggest you look at some of the motor drivers for things like treadmills which tend to use high voltage d.c. motors.I would be surprised if you couldn't find a mains-input supply designed for driving 20 LEDs in series for your Crees.

author: Rufus
author_rank: Super Contributor
timestamp: January 08, 2014, 04:25:39 pm
content: Quote from: trs80 on January 08, 2014, 02:54:07 pmIf you want simple, reliable, and little chance of it being a large source of RF interference I suggest buying a Mean Well constant current supply for each LED/chain. The voltage on the CREE chain is getting a bit high and you might need to split it in two.

author: made2hack
author_rank: Frequent Contributor
timestamp: January 08, 2014, 08:50:56 pm
content: As @jmole recommended, I tried TI's Webench tool, however, another road block. I keep getting "Your solution is not yet Webench enabled".When I click to show parts were not found, a list of components and circuits comes up with comments such as "Current Exceeds Limit" or "Calculated duty cycle exceeds limit".Now, I tried both 1 LED (39Vf) with a dynamic resistance of 4.1 Ohms and 5 LEDs in series (195Vf) with a dynamic resistance of 20.5 Ohms.According to this PDF by TIDynamic Resistance, I tried the following calculations by drawing a tangent @ the current I wanted.The graph is from Nichia for the NSCWJ216A LED. I drew my tangent @ 1800mA and a square around the max-min values. I guesstimated 42V as the max Vf (since more than 2700mA and the LED burns), and the minimum at 31Vf (since it tends towards 0 amps).So, according to dynamic resistance, ?Vf = 42V - 31V = 11V. ?If = 2700 - 0 = 2.7A. rD = ?Vf/ ?If = 11 / 2.7 = 4.07? ~ 4.1?. That was my value for 1 LED. For 5 LEDs in series, my dynamic resistance is rD-TOTAL = n x rD + Rsns. I think this would be 5 x 4.1? = 20.5?. I used that value. I then used all kinds of different Ohm values none of which seemed to work.Did I do an incorrect calculation? Or should the Webench app be used with AC current @ the beginning for a solution? I used DC current with Vin Min of 15V and Vout Max of 48V.Thank you all for your replies!