Tech Questions

[grizzle]

I have 3 allegedly "1 Watt" 850 nm LEDs, like Luxeons, but not made by the same manufacturer.
I wish to simply wire them up with an adapter and resistor (each separately), but when I asked on the company's forum (their technical "support" division), I got a bunch of smart-aleck remarks and no answers. I was wondering what resistor value and adapter amperage (for a 12 volt adapter) I would need for the following specs:

Vf: 1.4~1.5V
If: 350mA
Ipusle: 1000mA
MCD=50@ 350mA, MCD=70@400mA

If you wouldn't mind, could you tell me what "lf", and "lpusle" mean?
I assume "lf" means the milliamps required. Thanks very much for your time! :wave:

 

[Marduke]

http://ledz.com/?p=zz.led.resistor.calculator

http://www.led-calculator.com/

http://ledcalculator.net/

If is forward current.

 

[J_C]

Those specs look wrong, with only a 50mA current increase between 350mA and 400mA, it is doubtful the MCD would jump as high as from 50 to 70.

Unless you have an aggressive design and good heatsink, factor for the 350mA. If is forward current. Ipulse is pulsed current, you can use a short duration pulse at a higher voltage but they only rate up to 1000mA. For your purpose you can ignore this rating assuming your 12V adapter has some capacitance on it's output like a typical wall wart would.

Rating of the adapter would depend on how conservatively it is rated. For example industrial warts should be able to run 24/7 for years at the max rating, but a consumer product wart really shouldn't be loaded much beyond 50% capacity for long term use, especially in higher ambient temperatures, as it will eventually blow the thermal fuse embedded in the transformer windings. This is assuming only a crude unregulated wall wart, with a switching wart you have concerns about heat too but not the thermal fuse.

So I suggest a bare minimum of 500mA rated supply but really closer to 1A would be closer to ideal. That's per LED, if you're running them all off the same supply I'd go with at least a 1.5A rated supply.

Marduke provided calculations links, generally speaking it looks like for the spec'd 350mA you need almost 31 Ohm resistor in series with each which is an uncommon value, 33 Ohm -OR- 22 Ohm plus 10 Ohm in series for 32 Ohm total per LED would be a practical solution.