Suitable driver for a 3*XM-L2 bike light setup

Hi!

I'm currently having a project in school were I'm supposed to design and make bike light. So, now I'm on the hunt for a suitable driver for my this build. The light will come from 3 XM-L2 U3 emitters on 20 mm MCPCB's. My plan was to use the b3flex driver provided by Taskled, but as it seems now, it won't be in stock until early march and that doesn't include the shipping from the US to Sweden... I can't just wait that long for it to arrive.

I've also seen that Cutter AU stocks it, but the shipping cost is horrible, and after reading some reviews it seems like you really shouldn't be in a hurry when ordering from them... So thats not an option for me.

I will make the housing myself and can therefore adjust the size to suit the driver, but I'll try to make it as small as possible. The battery will be chosen to suit the driver, so both buck- and boost drivers could be of interest.

Do you guys have any suggestions for a driver that suits my needs? I'll be more than happy for any kind ideas that could get this project moving.

3 18650 in a series and this driver
http://kaidomain.com/product/details.S020148
yuo cans erach the site and the rest of the chinese sites (i.e. lightmalls, bangood) for similar drivers

or this with 3 batteries
http://www.banggood.com/LD33-Circui...L-LEDs-in-series-For-Flashlight-p-911622.html

I'd take the second one over the first. The first one was not designed for 9A, it was modified. You can tell because of all the sense resistors stacked to achieve that high current (the little rectangles marked R20), and the inductor had to be made so large it wouldn't fit normally on the board.

The second one running at much lower current will likely be much more efficient and run cooler, not to mention which it would likely be more reliable, and it looks like better construction.

I would be prepared to run 4 cells. Many buck regulators need a volt or more of overhead (input voltage higher than the output voltage). You MAY find that the output drops significantly as the battery voltage drops toward the LED string voltage as it discharges. Of course, you may also consider that a good thing, warning you your battery needs to be charged. This is especially significant if you end up with emitters that have Vf toward the high end of the possible range.

Oh, and if you're in a hurry, don't order anything out of China. New Year started this week and everything is shut down for two weeks! I think Taiwan and Hong Kong are still running though.

If you care at all about efficiency, buck (or in limited cases, linear) regulators are generally the most efficient.