# Luxeon K2 LED drivers



## 10492 (Jan 4, 2010)

http://www.national.com/analog/webench/led_architect


This might help.

It's free and chock full of stuff.


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## LightsRus (Sep 12, 2010)

First you need to define the allowable battery voltage. 
12V is a nominal figure, and each will have different lower cutoff; e.g. Ni-Cad, Lead Acid, NmH, etc. 
Lead acid is usually about 13.78V fully charged and you don't want it to dip below 11.75V or you can kill it. Ni-Cads start out with much lower terminal voltage charged, but you can suck them down till nearly nothing, and deep discharge is actually advised to kill their memory. You should look those up, my memory has failed me a few times.

All that said, lots of economical drivers are out there. Dnkldorf sent a good link.

The Zetex ZXLD1360 (following) is very universal and cheap enough to allow one per each LED string. They can be ganged with the control input so all behave the same. 

http://www.diodes.com/zetex/_pdfs/literature/pdf/SCLEDOV4.pdf

Be careful with the heat when you get those things up in current.
Cheers


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## Electric_Light (Apr 6, 2010)

Skipp said:


> I am trying to design a LED lighting circuit using 12 volt DC battery power. I am stuck trying figure out the LED driver needed. If I have four Luxeon K2 Stars rated at 1000ma each, with Vf of 3.72 volts.
> The largest LuxDrive "Buck Puck" is rated at 1000ma. So if I wire these in 2 parralell strings, I would be cutting the current in half (500ma) to each LED pair. In series I would be over my 12 volt max (4 x 3.72 volts), so can't do that.
> 
> The spec sheet for the driver puck says I can run up to 2 strings of three Luxeon LumiLeds (6 total) rated at 350 - 1000ma ea.. How is that even close to possible with a driver that puts out 1000ma Max?
> ...


What does the driver's spec say for actual drive current? You can run four on series on a 12v supply (usually automotive ones are rated 10-15v) using a driver with solid state buck-boost circuits. The drivers of course create heat, so remember that system efficacy at LEDs at running temperature and driver loss is substantially less than doing simple math with the most favorable figures from LED spec sheet.


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## Skipp (May 23, 2010)

Electric_Light said:


> What does the driver's spec say for actual drive current? You can run four on series on a 12v supply (usually automotive ones are rated 10-15v) using a driver with solid state buck-boost circuits. The drivers of course create heat, so remember that system efficacy at LEDs at running temperature and driver loss is substantially less than doing simple math with the most favorable figures from LED spec sheet.


 Here is the spec data. There is also a PDF if you click on "technical specifications" I just don't undestand how a 1000ma driver can power any parralell configuration of more than one 1000ma LED. But the PDF shows diagrams of 3,6, even 9 Leds being run off this one driver. 

http://www.luxeonstar.com/1000mA-Non-Dimmable-PowerPuck-Driver-p/2008b-1000.htm


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## Electric_Light (Apr 6, 2010)

There are three different models. 350mA, 700mA and 1,000mA if you read the PDF. It's a buck converter. It says that Vin must exceed Vf total. 

Input voltage 
32>x>n+2, but n+2 is to be not less than 5 for 350mA model, for others its not given.

This thing is full of conditions. It shows the optimistic conditions. The efficiency is based on ideal conditions too. It's not 95% across. It's 87% at 20v Vin for example. If the LED was getting 75lm/W at room temperature, you're down to 56 lm out the emitters per watt from power line. 

Realistic efficiency of power system would be like 85% AC-DC power supply and 87% driver efficiency yielding 74% input power to power provided to LED efficiency.

As for current output
"Measured with single emitter; output current drops slightly with additional series junctions to limit maximum power dissipation."

The figure five connection drives each string at approximately 1/3A. You can't use red LEDs for one string and blue LEDs for another though as the current sharing won't be even. The reason being the Vf are substantially different.

If you run 1,000mA rated LED strings in parallel on 1,000mA source, then each string gets 1/n amps where n= number of strings. 1,000mA LEDs are rated for use at up to 1A, not that they require 1A to operate.


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## Skipp (May 23, 2010)

Oh I get it now. The 1000ma LED does not need 1 amp to work. It can run on say 700ma just won't be as bright as 1000ma. And the 1000ma is what I don't want to exceed. 
I know about not mixing reds, blues, greens etc. I am only using exact matches of cool white. I also like those Luxeon Endors that are 3 seperate leds on a single star package. I also realize the Vin needs to be higher than total Vf. I have that part figured out.

NowI need to calculate what size solar panel to get for daytime charging of the battery. I was thinking of a SunLight controler that will control charge and Dusk to dawn lighting. 20w at 18-22 volts should do.


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