Looking for a boost driver for a 1 cell 12V build, anything exist in 17mm size?
Kinda doubt it, as the coil would necessarily have to be substantial.
I’ve got plenty of 1- or 2-cell AA to LED boost converters (~800mA), but that’s not what you’re looking for.
yeah im thinking more XHP35 in a 1 cell.
AFAIK, not quite?
All I've found on the subject is https://budgetlightforum.com/t/-/31239/113 and https://budgetlightforum.com/t/-/39445/28
I haven't done too much research, but in the bit I've done, I didn't see any working prototypes. Maybe someone else knows more, I haven't even fully read the linked threads.
I do know there's more than one working 20mm boost driver, including one for sale on Kaidomain (no idea how good that is, it was just on a bookmarks list I had for this very same subject)
This about the best I have seen for 17mm.
https://www.fasttech.com/products/0/10002000/1143101-1-2-aa-aaa-1-18650-1-mode-1a-led-flashlight
And here some that will work for a XHP-70 6v but none in 17mm.
http://www.kaidomain.com/Search/SearchResult.boost
There are a few members on the forum testing one now and I believe Richard at Mtn Electronics is also working on one. Either way it will be another month most likely before anything is available to buy.
I believe the problem is power in equals power out.
12v at 1 amp is equal to 4v at 3 amps input.
It must be hard to find a way to boost voltage by 3 times and out put 3 times the current from a single cell.
I’m no expert but good boost drivers are hard to come by and the drivers at kaidomain are about the best I have seen from a single cell.
I’m no expert either but we pull 10 amps from 18650’s continuous in some lights and vapers beat them up even worse yet somehow they seemed to manage to get 35watts from a 17mm boost driver with fully featured firmware.
See this thread:
Shocki, Lexel and Texas_Ace posts mainly.
Lexel has said he expected to have the driver ready in February. Later he indicated he lacked time so I wouldn’t be surprised if there was a delay.
But anyway, a superb 17 mm boost driver is on the way and actually pretty close. 
Not quite what you asked, but Mountain Electronics says the 17mm MTN-BST2 Boost Driver will power a 12V LED to ~1.3A (XHP35 HD / HI) but is Output voltage limited and will not drive an XHP35 to its full potential, but good for a ~1A efficient output XHP35 driver.
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Is there a 17 mm boost driver that can drive LEDs with high forward voltage with a single cell?
Like boosting a 18650 to 4.5 V? That would be great for UV and green lights.
I finished building my own Gxb172 boost driver and it work very well:
Size in 17mm and it use single cell input, and up to 50W power! Other people like schizobovine and moderator007 also succeed in building one. It definitely work for XHP35 in 12V output mode. I’m also sure it can be modify to drive higher voltage UV led.