# 12-16v led driver for a 20W LED



## yosh (May 21, 2011)

hi, i got me a 20W LED (ebay) and looking for best way to operate this by battery pack. i'm going to use it for my hand held image projector.

spec of led is :
Forward Voltage : 13.5V-15V 
Forward Current : 1500mA 

using my bench power supply, i am happy with the light output (cant measure but i guess 75%) using a 12v power source (@ 0.6Am). 

now, that 0.6Am was not limited by me. my PSU can output up to 5Amp and when running @ 13.5 it does output the 1.5Amp the LED expects.

so... 
1. should/can i use a 12v/6Amp (gel pack, available locally) without any current limiter?

2. should i get a led driver . and if so, what driver should i use. 
i've seen some 1$ current regulators based on the LM317 but then you pay with heat and a voltage drop . [edit: i think i cant use an KM317 with a 12V battery as the 3v drop is too much > see this thread) 
all i've seen online expects 85-220v (sk.42741)
[EDIT2: a better driver chip?] i stubmled on the LM3410, which looks like a nice one. 
hope i can get it fast enough (pdf, schematic ). 
mods: please move to correct sub-forum, i hope its the right place for this.
i tried serching for 20w led driver and didnt get far.


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## bbawkon (May 21, 2011)

Just curious; why use that LED? It's horribly inefficient compared to say the Cree XM-L or even the SST50/90 chips. You're going to deal with about twice as much heat for any given lumen output as you would with the XML. The XM-L also has the benefit of being a 3ish volt part, which means you could use one of the many available buck drivers (dealextreme or ebay) for stable light output across the battery discharge cycle. Remember too that with one of these more efficient LEDs, you'll get roughly twice the run-time on a battery charge.

If there is some reason why you like that particular LED, then you're definitely going to need a buck-boost converter/driver. I suspect that as the battery discharges even just a bit, you'll fall below the minimum vF and the led will not light at all if you drive it directly.


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## deadrx7conv (May 21, 2011)

A fully charged 12v battery is usually 12.8 volts. 
Charge the battery fully. Connect your volt meter. And keep an eye on battery voltage, light output, and running time.... to make sure you have enough of all.... 
If you're happy with the output over time, you do not need any driver. 

Can you use AC or must you use a battery? 

If your test fails, you could also use 2-smaller 12v/3amp or 4amp batteries in series(24v) and regulate that to the 1.5amps. http://www.cutter.com.au/proddetail.php?prod=cut755 http://taskled.com/hbuck.html

Make sure LED has heatsink/propercooling.


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## yosh (May 22, 2011)

thanks for the comments guys,

@bbawkon- having a single light emitter is important for my application, as a projector needs better optics to handle multiple light emitters.
i need both mobility and lumans as i will operate it in a crowded semi-lit gallery. but i think i will order a few XM-L and try.

@deadrx7 - thanks for the link, looks like a nice driver.


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## bbawkon (May 22, 2011)

If this is for a projector, you really might want to look at some of the bridgelux leds. 1000 lumens really isn't that much in a projector scenario, and if you're talking a semi-lit gallery, lumens requirements are going to be high.


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## yosh (May 22, 2011)

i've seen some links here to there new offerings up in digikey, i'll just need to match it to the correct driver.

[edit] but there Vf is 28.6, what booster should i use? (digiky link)


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## bbawkon (May 22, 2011)

linkswitch-tn is a good choice. there are a lot of good choices.


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## yosh (May 23, 2011)

thnk you, i think i will continue working without a driver for now. 
a 12v gellcell in my case. are there any side effects to that approch, aside from the lumans hit?


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