[[ GXB20 Driver – Homemade Constant Current Programmable XHP50 Single-Cell Boost Driver! ]]

That looks so neat. :+1:
The side picture gives another perspective to the difference in height size of the components.

Were you able to hit the 95% efficiency goal? Remarkable work here.

I see that the top says GXB20 V2.0 3V/6A. Is this a typo 3V/6A? What final voltage, amperage, efficiency did you get? And finally thanks for helping us out on getting a good single cell driver for these newer XHP LED’s.

Nice work! It’s a beautiful driver!

Ah >< I was hoping nobody would notice the typo , but yep it was a mistake in the silkscreen - it's supposed to be 6V 3A. But I think I can claim that the nominal input power is ~3+V at 6A, so that's still ok :).

The efficiency numbers are roughly the same as the chart that I posted earlier. Again efficiency varies depending on the input supply and the load, but realistically the converter should have a total efficiency ranging from ~85 to 95%. This is the total converter efficiency, with some additional loss in the current sense resistor. Maximum I've tested for the GXB20 topology is the same as the previous with a measured 3.8V in at 6.32A, and an LED current of 3.26A at ~88% efficiency.

However for the GXB20v2, I've measured a total converter efficiency of 92% with an input of 21.39W at 6.01A and output of 19.76W at 3.0A. I'm also pleased to say that the lowest possible brightness I got with the GXB20v2 is really low at an LED voltage of 4.52V and around 1mA, so it's a true moonlight, or more like fire-fly mode :). I have yet to fabricate a PCB with thicker copper (2oz) which will improve things a little more.

Regardless, as I've found, at such high power levels, just basic DC resistance plays a huge role in efficiency especially with low single-cell voltages. In practical aspects, I found it very challenging to avoid significant voltage drop at over 6A (at least with the cheap flashlight host I'm using), which I suppose places a practical limitation in how much more power I can push through. Any more and the voltage the driver sees becomes a little low, and overall efficiency also drops.

I know this is a bit off topic, but how would this boost driver with a 4500mah 26650 compare to a linear driver of the same 3 amps, but using a pair of 2200mah 26350 batteries?

Would voltage sag be about the same under the same load?

Is efficiency a lot less?

I know there’s a big difference in 18mm batteries because name brand 18650 are much higher mah than small brand 18350. But with 26mm there doesn’t seem to be the big difference.

Nice!
I wonder if it’s possible to get a smaller design with lower power. Like 17mm 9V/1A for 219C triple.

Low power buck drivers are already available.

Yes it's possible and with a lot lower power, can definitely be made smaller too. However it's unlikely I'll have the time to work on it but I'm sure there are lots of other who will be :)

I don’t recall any in the 17mm size beside the KD BD8P. Which is both out of stock and unprogrammable.
Also, a small boost driver would allow to build a high-CRI EDC light using XHP LEDs.

I do have a 17mm version planned for the future, but not quite now yet!

Thank you for bringing this little experiment of yours to BLF.
I am also one that is very interested in trying one, whether building it myself with your flashed MCU or a complete driver.

Might would have to build a whole new flashlight from scratch just to honor your work on this ! :slight_smile:

Great work!

The idea of a boost driver for the XHP LEDs has been floating around this forum for how long now?

Someone finally has a grasp of how to get it done! 2017 is looking like a good year, in more ways than one.

Would love to put this driver into a nice host, maybe Texas Lumen’s upcoming c8-sized host?

How sweet would it be if cree decided to offer the xhp70.2 with a 3 volt option? All 4 dies would be parallel.

Just dreaming out loud. Lol

I can envision this is a smallish light with a beautifully tinted MT-G2, sure would love to see it…

I would love to try one of these out as well. I am thinking 18650 powered mini C8 with an XHP50.2. After having build one XHP50.2 in 4000k for an old SupFire I have, I have really decided that I like this new led. I would be willing to build 1 to test if I had a programmed MCU and a shopping cart list.

Looks like good work to me!

great job

i am interested too

Building this on 17mm size would probably need a sandwitch of 2 PCBs to fit all components

On the other hand you could try to bore the C8 to 20mm and use a spacer to the shelf, no retaining ring just the driver between spacer and tube

Is that something you would sell or is it for personal use only?

Realy like the output of my ee x7 xhp50.2
But the driver is….not great.

Would love to put one in a m2 or similar host.

Thanks for your kind words! I’m currently working on a write-up on this project and releasing all open-source as well as offering the boards on oshpark so everyone can build one for themselves. I do have extra boards and I can offer firmware-flashed boards with MCU at a later time, but I really will not have time to offer built drivers. I do understand it’s a bit tricky to put together and I highly recommend either a micro-soldering station with magnification for hand-assembly, or even better if you have solder paste (can apply using a needle) and reflow with an oven or hot-air. Updates will be on this thread.

I’m not quite sure if it makes sense from an electrical point of view, since there’s really not much use case for it except in flashlights (which makes up a very small % of their sales), and that it’s not electrically efficient since resistive losses go up by the square of the current.

I’m 100% sure I can fit it all onto a 17mm driver with no less functionality and with a single PCB. Just need to find some time to do it!

It takes a while to assemble this together by hand only because it’s fairly small. So I don’t really have any plans to offer these for sale as whole drivers, unless I have some help in getting this mass-produced! Otherwise I’ll be releasing more open-source so anyone can buy the PCBs themselves on OSHpark or similar and assemble it