Let's Make Robots!

Luxeon Leds - what would be the simplest constant current driver for them

led5.jpg

I have just bought 5 of these 3W High-Power LEDs 

I could drive them off batteries direct ....

...however i would prefer to feed them with a "constant" but adjustable (350mA-750mA) current.

 

What would be the simplest circuit i could use ?.....

.... and would there be a way to PWM them?. 

 


Specs :-

3W High-Power White (6000-7000K) 130 Lumens - 140 deg

3.2-3.6V   750 mA /3W/110-130Lumens

 

Reason 1 for project :- I lost my cycle lamp (for "off track" riding) and would like to light up the forest with these babies.

Reason 2 for project:- There is also a high power RGB version which would be an amazing "psychedelic light up" option for Robots.

 

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Wow so cheap.......... i have ordered one and will report here on findings ...... lets see how long China is.......
hope it goes well. my previous ebay china encounters where pretty good with fast shipping

They took about 2weeks for delivery - however they where well packed and i am very pleased with the build..

....thanks Gareth

I am sure that you have seen these but if not, just wanted to let you know. Pretty slick if you ask me, i2c, adressable, wicked bright and they make a big one and a small one.

BlinkM and BlinkM Max

The Max version is new to me.......... and gives an impressive 445,000 mcd (2amp powersupply needed) for a RGB type. (i2c interests me :-)

EDIT:- I am calling thier "Bluff" regarding the above specs - there is no way they can achieve this figure and dissapate the heat generated............ (and they do not even quote the angle of emmision - bit pointless actually)

A  typical 100 watt incandescent bulb puts out around 135,000 mcd . ie none focused.

I am hope_ing that my white version will yeild 15,000 mcd  (350-750ma supply) or higher as i have also a sample pack of 10 different len_es to focus the light.

can you believe some Luxeon Stars  can reach 825,000 mcd

Cool LED link here to :-  http://www.gizmology.net/LEDs.htm

I dunno Gareth, I think the specs may be valid for those BlinkM MaxMs. Those large LEDs have both a large cone reflector backing and a large forward lens, with means that the emission angle is typically quite small, and they also have several dies per LED module. The 445,000mcd rating is for the whole trio of LEDs, so each LED (which is really 4 LEDs sharing the same housing) is spitting out ~148,000mcd, which is roughly the same as your example 100W incandescent bulb.

If we assume the MaxM LEDs have an emission angle of 25° (0.15sr), then the total luminous flux output is 148,000mcd*0.15sr = 22.2lumens, which isn't much compared to the ~1700lumens produced by the incandescent bulb. Not to mention the fact that the incandescent bulb is many times less efficient than an LED - much less heat would be generated by an LED array producing 1700lumens. Additionally, the MaxM has a built in PWM controller, so not only will the LEDs run efficiently but the current consumption will probably be a lot lower than the rated 2A in almost all cases.

In the end, the 'mcd' rating is a waste of time in my humble opinion - who really cares about light density? Total light output (lumens) and emission angle are the two properties that most people would really be interested in surely.

Thanks for shedding some light on the subject.

This makes me happy that my Luxeon is producing 130 Lumens (@750mA only) - wow it really puts things into perspective.

BTW:- i have found if you drive the Luxeon at low currents (i stress low current) then a heat sink is not really nessesary.

I agree the mcd rating is very missleading, so take heed all you High power led suppliers - (-: just send some samples to LMR for review purposes :-)

The easiest solution is a current regulator made with 2 transistors and two resistors. I use this design in some of DAGU's LED lights.

My schematic software isn't working right now but here is an Instructable that uses a similar circuit to drive LEDs.

Thanks - this is the direction i was looking for ........digging around on the site found this too  Instructable .

and this with PWM control