Hiya Dave,
I was just wondering if you have some time to dig back into the elusive 3A boost driver discussions and experimentation.
I actually have accumulated a couple of parts over the time for testing and do some calculations/play with LTspice from time to time. (While time is still somewhat rare)
There are some topologies that look promising (like SEPIC with (more or less small) coupled inductors) that I would like to experiment with in the near future. But I can’t say if that will yield any positive results. 
Hey,
still alive, and still interested in the topic.
Things were a little bit complicated in the last weeks so i couldn’t be here for a month or so.
(And I lost my lab access well before I expected, so I’ll have to build some lab equiptment before I can experiment in the future. What an unpleasant surprise …(Euphemism of the week ) )
So, some thougts on the topic:
I still believe this can technically be done, but it boils down to some quite expensive and not easy replaceable parts. Since price and difficulty of manufacturing are somewhat crucial to this project I have to admit I see no way to meet these goals for now. (This may change in future. Nice parts are released every day. Maybe one day it is an affordable, synchronous and monolithic converter that can handle the current. :-))
I still will try to build something comparable just for the fun of it of course.
(will update on that)
I personally would probably reduce the current in boost mode to something like 2A, would still be nicer than any non-boosting driver, but that is not really the aim of this thread.
Hi Dave,
Its great to see that you’re still showing an interest in this one. A 2A boost driver might be an excellent place to start, and it would certainly have many uses. Since several C8 sized lights use larger drivers than 17mm, perhaps a larger boost driver could accommodate +3A in the future (or maybe shift focus to a larger driver now if it seems more feasible at this time). At this point, we have nothing. If anything changes on your end, please keep us updated.
Anyone else have any ideas?
Well, looking at ecigs has given me an idea but it may not be easy to implement.
The Kick from Evolv has been around for a while. The linked one is the Kick 2. They are made so the kick and an 18500 will replace the standard 18650 cell, and then you have a VV/VW ecig mod.
But, you would be limited to about 4.5a with an xml2 to keep it at the 15w limit (rough calculation off the top of my head)
Food for thought I guess, though its not a standard 17mm driver size...
EDIT: They are not cheap. But maybe someone would be willing to reverse engineer one and build it on say a 20mm driver board. There may already be plans out there for a DIY Kick also
Dave, are you still with us? :bigsmile: If you have some time, could you please put some thought into what might be possible in a 20mm boost driver? Several 1 x 18650 lights have been produced with this size driver and might work out to become excellent mod hosts.
I found a “super booster” that takes 3.7vdc (Li Ion) and steps it up to 5vdc, capable of pushing up to 3.6A
Not sure if scalable or ATTiny13A controllable (for the modes and whatnot)
Github
https://oshpark.com/shared_projects/v8BhADlp
Not sure how well it would fit on a 17mm or what it would take to put the chip is capable of pushing at least 1 more amp more than the other “booster” type chips
Kick (variable wattage) duplicate from FT runs $8.33
http://www.fasttech.com/product/1501000-variable-wattage-kick-module-for-mechanical-mod-pv
I vape on 3 of em 
kick 2 (Variable voltage)
http://www.fasttech.com/products/0/10006524/1646300-variable-voltage-kick-module-for-mechanical-mod
Are you also wanting a “BUCK” driver to take stacked 18650 batteries and lower the voltage
Boost is stepping up, buck is stepping down
Thanks for posting. At this time, we are trying to find a boost driver that can maintain boost @3A (preferably up to 3.5A) all way down to 3V (or less if possible). A 20mm single layer board is also being considered. The general consensus in another thread I started was that vape drivers wouldnt work with LED’s.
Also, if the driver can Buck and Boost (as some can), then we’d have the best of both worlds.
Well that kick runs at 33.3hz PWM, and output volts is I believe 5vdc…unless there was a way to change that…the light would flash REAAAALY bad
Perhaps a side project, a boost driver that can feed one 6V MT-G2 from a single li ion (boost only)?
Also a good idea would be a buck (only) driver that use two li ion in series to feed the same 6V MT-G2
The voltages in a 2 cell/MTG2 setup is close enough there's not much to be gained from a buck driver, linear works fine and there's really not enough overhead for a buck driver to work properly. It ends up with very nearly the same limitations as a single cell/single XML2. MTG2 really needs 3 cells (or some combination using other chemistries that gives a higher end-of-discharge voltage).
The inefficiencies of boost circuits, delivering 3A to the LED, it would be pulling MUCH more from the battery (this is why vapers won’t use any batteries that won’t be able to push a minimum of 5A continuous…well vapers that know overdrawing a battery could cause it to vent)
Single cell MTG2 boost driver is electrically feasible, dunno if it would be able to fit on a usable sized PCB though, that's a different issue altogether. To get 18-19W output, assuming 85% efficiency, it'd only take around 5.5A input with a fresh cell, rising to 6.5A at the end. Battery life would suck balls, but a light small enough for a single cell isn't going to be happy for very long running at that output no matter what flavor of LED is being used.
I would aim for less powerfully driven but using 2 18350s gives less then half of one 18650 in watts
Not as much as I would like.
Well, how high could a 20mm driver be?
To visualize the problem with the 17mm driver again:
That is about the size of a suitable inductor in a P60 pill. About 8x8x8mm. You can go down to something like 7x7x5mm with cutting safety margins a little. Thing is, those are expensive inductors, something like 2…3 bucks. The ones for 50 cents can take more than double the area.
Of course price goes down a lot with volume, but I’m unsure what volume and max. acceptable end price would be.
So, it’s really a question of how high one can stack multiple boards and how much it can cost.
It’s a lot easier to do with an expensive LED driver IC that has it’s power stage and rectifier integrated than with a micro-controller based DIY solution. The latter would not even fit in a P60 pill by volume if you shredded it to dust. 
But in a 20mm one?
It makes sense to me to start with something feasible and then move on to more difficult projects. How about starting even bigger with a 25 or 30 mm board for 26650 lights or multicell lights and then move onward and inward. The effort would not be wasted as there are plenty of hosts that could use a larger driver. Let’s do the driver circuit and then work on miniaturizing it.
If you hung in there and mulled over your available parts selections and options, would you be able to estimate a reasonable maximum height for a stacked 20mm version? If it seems doable, Im sure that many of us can start taking some of our lights apart and get a few measurements.
That pic certainly does put things into perspective for the 17mm and how difficult a 20mm version would be to design. Sheesh! Although a larger board, does anyone know if the DQG triple xp-g2 driver (I assume is a boost) might offer hints for parts and construction? Im beginning to wonder if we need to start with a fresh clean slate or if we could possibly garner a few hints from other designs. Yeah I know… Im starting to think like the Chinese in “borrowing” other designs.
I doubt that's a boost driver, 1250 lumens from 3 XPG2s only needs 4.0-4.5A total depending on whether that's including losses from the optics or not.