[ GXB172 - 50W Single Cell 17mm Boost Driver! ]

Just replied to your email and then saw this. Definitely interested in the 20mm. The GXB202?

- Clemence

20mm is too large to fit inside the S2 but upon more thinking I’m not sure what kind of reflector or optic could be used with S2 and MT-G2 combo.

Keep in mind the loneoceans is not going to offer his 17mm for sale. He shows the plans then you have to build it yourself. That’s why I mentioned Lexel. He will be building and selling them, but not a boost driver in 17mm.

I wonder if the Convoy M1 or M2 might fit a 20mm driver. It’s head is a little bigger plus it has a bigger reflector which might work better with the big MTG2. Research would need to be done.

Hm that's not what I said :). I said I didn't design the driver with the goal of selling and making money off them. If the driver turns out successful, probably will find a way to get a batch fabricated and assembled. ^_^. But if lexel or anyone else gets a working driver for sale, that's fantastic! Always better to have more drivers :)

My bad.

I hope Lexel or someone is able to offer it.

Hello all,

Alright more updates..

TL;DR: GXB172 works great for XHP35 (HI), driving it at 2.5A 14.7V. Power source was a single LG HG2 18650.

I finally got my hands on an XHP35 LED on a MCPCB (from Kaidomain), so I could do some real life testing of the GXB172 driver on 12V (4S die) LEDs. The candidate of choice for this test was a XHP35 HI, 3000K, C2 30G 80CRI LED. The light was mounted on a medium sized heatsink for testing and connected to my GXB172 in 12V mode.

For this test, the goal was to run the XHP35 HI at it's maximum output (before output starts to suffer).

I referred to Texas_Ace's excellent experiment here: https://budgetlightforum.com/t/-/43473. From this, I determined that 2.5A was the maximum one would want to drive an XHP35, after which you get no additional lumens and run the risk of damaging the LED.

Soldered up an XHP35 and connected it to my GXB172 dev platform... and turned it on.

... and... it works!

Note that based on my previous work with putting together an actual 17mm driver, the 17mm PCB performs at least as well as, if not a little better than my 'dev board'!

So I fully expect the GXB172 to work just as well, in the form-factor PCB.

Test was conducted at a variety of power levels all the way from the lowest setting (about 2-3mA @10.2V) to the LED, all the way up to 2.50A at 14.70V (36.75W to the LED). Battery input was measured at just over 40W, so about 90% total efficiency (including wires etc, probably a little better in a well-put-together flashlight), with higher efficiency (>95%) at more realistic power levels.

I plan to have this LED put into one of my old SK98 hosts since that has a zoomy lens. This should make for a pretty nice 'budget' throwy light, and pair nicely with my 144 Convoy S2 'floody' light!

So stay tuned for a 20mm version (since that needs a 20mm driver).

Thanks for following this project and as always, more to come soon !

Very nice! I have wanted an xhp35 HI in an EDC for a long time.

Hmm, now I start wondering how much power it can put out for a triple xhp35……

I know, I know. Never satisfied.

What. You want to put it in a Sofirn C8F? Lol

lol, actually I had one of those hosts in my cart for exactly this until it went out of stock.

Speaking for myself - I want XHP35 Carclo triple.

This driver won’t make it hotter than Emisar D4. But it will make it more efficient for much higher sustained output.
But I don’t really see a host sized similarly to D4 which has space for inductor….

Lucky you! C8F hosts are back in stock.

MTN Electronics caries that host as well.

As always I’m interested in the schematics. Any idea when you are going to show them?

I’m going to be doing a 2-year college project as I am studying electrical engineering. For my project I am making my own CNC-machined bike light from copper using an XHP70.2 Emitter. It would be really helpful if there were some schematics to look at in the mean time as I am currently prototyping some PCBs that I made on Easy eda.

Where to buy LoL?

Could these be realistically offered in kit form? Chances for EU fellows to acquire at reasonable money?

How about a buck-boost driver? It is amazing you've handled to fit this boost engine over just ∅17mm, could we see a ∅20mm 1S emitters buck-boost engine in a nearby future? In obtainium materials, :-) of course.

Regards and cheers

The GXB20 you made had a circuit diagram along with a detailed bill of materials. Would you be able to do the same for the GXB172 because I would love to see how this driver works in such a small overall size. Please feel free to contact me at my email: jasonlee422001@gmail.com

Hello Jason,

Since you're planning to drive a XHP70.2 with two cells, I'd highly recommend making a linear constant current driver instead, with an optional direct drive mode (though personally I don't like direct drive FET drivers). The GXB172 is a boost driver and boosts up the voltage from a single cell to the 6-7V required to drive quad-die LEDs like the XHP50/70 etc. However since you're using two cells, there's no engineering benefit to make a boost driver.
I'd recommend keeping the two cells in series, and you can design a high current but regulated current driver. This can be done with a feedback mechanism using a pass-FET, an opamp, a current sense resistor, and some sort of control (e.g. via a Microcontroller or potentiometer) to generate the desired reference voltage for the desired current.
I do not have any schematics for the GBX172 yet because it's still in development. That said, there's really no secret or magic to it - it's essentially a synchronous boost converter, and if you search that you'll see tons of the exact same schematic online. I'm using the MP3431/29 IC, and if you look at the datasheet, you'll see the full reference schematic. Likewise, check out the TPS61088 if you're interested in boost drivers.
Good luck with your project!

So when can i order a 17mm? :wink:

You could probably order a 17mm driver, then put on the parts yourself, and flash the driver.

I’d pay a nice buck if lonoceans was willing to make a group buy for the bare PCBs

Quick update... if you recall, I started the GXB driver project with the original intention of putting a XHP50 LED in one of those chose SK98 flashlights. Since those hosts come with a zoomy lens at the front, I thought it would be a perfect candidate for a XHP35HI for a low cost but pretty decent thrower. The SK98 requires a 20mm driver and a 20mm MCPCB.

I didn't have much time to do much but I did do a super quick modification of the GXB172 and... here's the GXB202!

The larger board size allows for much better clearance around the board as well as more space for larger passives.

Here's another view of the driver board after assembly.

For the LED, I chose the highest bin XHP35 HI I could buy (sadly only a D4, 5000K). This was installed into the pill with Arctic Silver thermal paste on a 20mm copper MCPCB.

And the driver was also installed. Note the GXB202 was configured for 12-14V+ output with a maximum of 2.5A drive. TA measured 2570 lumens from a E2-bin LED at 2.5A, so this should be putting out a good ~2396 lumens.

I then put the light together with some improvements to the tailswitch and paired the light with a LG HG2 cell, and the driver works great! More to come soon.