>> Homemade Gxb172 led driver (complete!)

I make current measurement today. So far after playing with flashlight for entire day, no problem yet!

For low values, I use multimeter in Amps setting. For turbo mode, I use wire and extech clamp meter (but 2.5% error+some digits). Battery used is LG HG2. I also solder J1 and J2 to test turbo mode at 5.5A. Default turbo mode is 5A. According to Loneoceans current chart of current to 6V LED, here is the tail-cap current I measure:

  • Moonlight (<10mA) - 12mA
  • Candle (no rating) - 20 - 40mA? Jumps around
  • Low (50mA) - 72mA
  • Med (250mA) - 390mA
  • Bright (1A) - 1520mA
  • Turbo (5A) - 11.2A (clamp meter)
  • Turbo (5.5A) - 12.4A (clamp meter)

Be careful - tail current only applicable to my battery, if you use better battery, current may be less. It seem like with changing resistor or firmware, much more current can be achieve!

However at 4V battery voltage, 12.4A is already 49.6 watts!! Please let me know if anyone want to know more test.


Overall this was very interesting project to solder. Although I have soldering experience, Gxb172 was still difficult to solder together, but easier with practise. I recommend using usb microsocope or magnification during soldering, very small solder tip, very thin solder wire, and hot air. For mistake, thin solder-wick is the best.

I also suggest using flux pen and needle tweezer. For cleaning, I use cleaning alcohol and cotton swab. Solder for temperature IC is most difficult because it is very small, so I suggest using no solder, only flux. High heat and low air speed. Inductor is hard to solder, but just keep at ~270C air heat for a while and it will solder.

Finally, before assemble I suggest to test with multimeter to make sure no shorts, then test before putting into flashlight host.

For program, I don't know of easier way than using pogoprog, but you can also use thin wire soldered to programmer. I use Atmel ICE, so I have no idea about USBASP, but moderator007 has used it to program so it will work.

Difficulty - 7/10

Cost - 8/10

Brightness & result - 9/10

I hope to be able to get firmware to change for even more current, or I may have to do resistor mod

I added a .05 ohm 805 resistor stacked on top of the .01 ohm for .0083 feedback and run’s slightly over spec’s . My meter read around 15 amps with a 30Q but it could be more than that.
My Fluke 87V is only rated for 10 amps. I don’t have a DC clamp meter. Increased light out put a little over 300 lumens.

Nice write up. I’m really hoping we can inspire some others to follow. For a single cell light, it’s a beast of a driver. :beer:

Have you thought about using a DIY current shunt?

Using something like a 5-10mOhm wire would be good for measuring such high currents.

This is how I actually do it.

I haven’t tried that yet as I feel the 87V is pretty close. My numbers before the resistor mod, pretty much resemble clientequator’s at each mode and jumper setting.
I may end up buying a clamp meter, but I think I have hit the upper limit with this driver. If my math is correct I’m guessing around 55 watts in.

I want to post update here to show my finish Gxb172 flashlight combine with Gfs16 mosfet switch and led tail light!

After finish my Gxb172, I build the Gfs16, my post is here #134: https://budgetlightforum.com/t/-/50404?page=4. Here are photos from this project:

Review for gfs16:

This project is easier to solder together than Gxb172. The hardest one is soldering the tiny mosfets on the led board. The rest is easier than Gxb172. I am not sure why schizobovine have problem with battery, since mine work first time.

Same as Gxb172, I recommend to use magnification to solder with smaller solder tip, thin solder wire. I only use hot air for the lfpak33 mosfet.

Before assemble, I suggest to make sure lfpak33 have no short, battery have no short, and led light system voltage working with power supply. For me I use oshpark 0.8mm pcb for both and they fit Convoy S2+ good.

I recommend the hobby maker to order more tiny mosfets before you blow them on the floor, and I recommend making sure you buy the correct Convoy s2+ light to make sure it fit the stainless steel switch! Make sure you handle tiny battery carefully! Also I use very thin wire (awg30?) to solder + and - pad together. I make sure I keep the switch screw tight, but not overtight to prevent pcb from breaking because it is not as strong as aluminum washer.

Difficulty - 6/10

Cost - 5/10

Result - 9/10! Very nice! I remove one point so it is not perfect so loneoceans can motivate to improve it

I recommend loneoceans add more led on the tail to make ring of light, but I understand how it may have no space since need two bank of leds, and any smaller is harder to solder.

Final bonus photo of S2+ in snow! I am disappointed because it didn't melt all the snow , but flashlight make the snow light up very bright from inside!

After using this light a while, I think actually I mostly use 'low' and 'medium' mode the most. Moon light mode useful during night-use and the ramp help to prevent blinding me. The turbo is too bright and only useful to show off to friends, but still a fun project!

Big thank and appreciation to loneoceans for this cool project and for everyone here who also make their own and inspire me to build this successful project!!

Nice build! I like that snow pic! :sunglasses: :+1:

Thanks for this thread, I had been on Loneocean’s site and the gerber files dont seem to be there nor the firmware, etc only the schematic.
Ive found a github link for the firmware, but still reading up on whats required for the build.
Are all the modes set by jumpers? You dont need to modify the code to set your custom brightness levels?

Im up for the challenge to build one, ive done SMD work before, but I will get a bunch of boards made from JLCPCB, they also offer an SMD assembly service, so if thats cheap enough, I may as well just get them to make me a bunch of boards.

Loneoceans also is the same person who designed the universal driver 2.7 revision for a DRSSTC, (musical tesla coil) I have built one using his driver board and it is of excellent design. :slight_smile:
Thanks Loneoceans if you are reading this :wink:

Please keep us updated :+1:

This is Loneoceans thread for the GXB172. [ GXB172 - 50W Single Cell 17mm Boost Driver! ]
The mode groups can be changed by 2 jumpers X1 and X2. Their description of the settable mode groups is on Loneoceans GXB172 page on his site.
Its about 3/4 the way down the page. Any of the modes can be changed in firmware by adjust the value anywhere from 8 to 1024 I believe. Seems like it couldn’t go any lower than 8. You’ll have to experiment with the low setting.

Yes I had been on that thread, I got stuck on the wrong page of his website, i was looking on the GXB17 page instead lol

Right now im figuring out what the best way to reflow the parts on the board. Did you use a reflow gun or an oven?
I have neither of these.
Ive ordered a USBasp USBISP and will design a jig for the programmer probes that can be 3D printed.

Does anyone know of a service in china that can just do all the SMD work? It will take some time to assemble a single board, and I probably will want to make several for myself.
I see JLCPCB can do this, but only on one side of the board. Im tempted to get a batch made and work out a group buy or something similar.
There definitely is a market for this driver if we can get enough people to buy the initial production run, I could get more made at a better price.

That would be great, I would definitely be up for a few of these drivers (the GXB202).
The cost of making these locally here in the States is quite prohibitive, think almost 3 Grand to get a hundred done initially.

$3K is actually quite cheap considering it works out to $30 per board at that price and would cost me more than that in parts to make a single board.
Im sure we could get the price down far more if someone in china can help out with production, either way, we will need a group buy to fund the initial production run and still will require labour to program them all.
I wonder if Mountain Electronics are interested in stocking this driver?

And i’m looking for someone who would build one of each size at least.

We could ask Richard (MTN)...

Im on PCBway getting a quote at the moment and its about $440 for the boards and assembly costs, but have no idea on component costs yet as im trying to get the right format of BOM file sent to them as well as a centroid file which I have no idea how to make from the gerber files.

Geezs...and i don’t know any of these words you’re saying ...

But i support you!

If ya got the files from OSHPark, just send them the whole ZIP file, they can work with that and make the paste stencil out of it as well, it’s all there. My local quote for all the parts was about 1500 bucks, and at least through Digikey, I can get them to preprogram the MCU before they send it to me.
Now that I am thinking about it, it might be most economically viable to just make the 12V version, since it will cover all the bases in one go, at least when it comes to the Cree LEDs

Thats good to know Digikey can program them. I dont think the person understood what I was trying to tell them from the PCB company. It wouldnt let me upload the gerber files alone (i did upload the whole zip file) but wanted me to add a BOM file and the centroid file before it let me click submit, so ive been communicating over email.

Anyway, ive been in contact with loneoceans and he will be able to help us out with the required files. :slight_smile:

I've sort of followed this thread from time to time. Nice to see it is gaining some momentum towards getting a production batch made. So go ahead, make my day. :-)

Is the 12V version able to drive 2S/6V emitters equally well?

Concerning power input, other 12V boost drivers can be fed with 2S cells. Thanks to a much higher input current, with 2S cells the power at the emitter would reach ludicrous levels with this driver. Is this feasible? LoL!

Not gonna buy anytime soon but since this initiative is in its early stages, count me and my axe in. :-D

Let me know how many you need.
Once I get price confirmation, I will go and start a new thread to feel out how many pre orders we need, likely the more we can do the cheaper we can get the costs down, but at a guess, we should be able to get the unit costs well under $30USD per board im hoping.
for 2S lights, mountain electronics has a very good driver already that can be ordered with custom firmware. but as far as 1S lights goes, this is the only real decent driver I can currently find.

Considering the fact that I can build them locally here in the States for about 25$ apeice, that should not be a problem.
Hell… If I would have garnered any interest, I would have plinked down the initial cash for the startup, already got a local quote and everything ready to go.

Anyhow… :wink:
Personally would love to have a Convoy L21 with a 70.2 popping in at 6K+