I build this driver for 6v at 50W: [ GXB172 - 50W Single Cell 17mm Boost Driver! ]
But this also work for 12V led. For example moderator007 make one for his xhp35 led and he got 2600 lumen!
Some boost driver use tps61088 but that has max output voltage at 12.6V. loneoceans gxb172 use mp3431 and can have up to 16v ouput. this driver come in 17mm and 20mm version also.