Cree xr-e Q5 with 4AA NiMH


Newly Enlightened
Dec 13, 2008
Hi all (my first post)! :wave:
I would like to build a LED light for my bike based on the Cree XR-E Q5 LED and was wandering what's the easiest way to drive it? I would very much prefer standard AA NiMH batteries. Also, as I don't have a 4-channel charger, 4 AA batteries would be much simpler to charge than 3.
Is a direct drive (with a resistor) a valid option? If not, can you recomend a good regulator circuit on DX with a good efficiency?
I will also probably need a lens/reflector? Maybe something in the range of 30degrees spread. Any recomendations?
I have discovered the DX site a few days ago and still haven't stopped drooling :)


Flashlight Enthusiast
Dec 5, 2007
Las Vegas
I am not trying to be rude or anything, but I don't really see why this should be in the bike forum, it is really an electronics question regardless of the mounting.

Yes, a resistor is a "valid" option. There are resistor calculators availible on the web to help you choose. Here is a popular one:
Keep in mind of course that you won't really know the "diode forward voltage" that is being asked for, you can only guess at it. And that depends on your drive current. Perhaps call it 3.5V and drive it at say 700-800 mA. That will give you a little leeway if your calculation are wrong.

Another option may be a "linear" regulator, perhaps one based on the amc7135 (do not attempt this with 4 alkalines, but you should be fine with ni-mh)

The driver board list thread will be the best place for you to do your research:

And of course, keep in mind you can't just drive these emitters bare, they will need to be properly heatsinked or will fry very quickly, like in less than a minute.

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