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

Wow very exciting work! More people building the GXB172, but this looks like your design! Do you use the same MP3431 ic? I see different component on your board, like maybe bigger resistor and different regulator and attiny?

Nice Design Mike C. Looks like your using 0603 components. Is this PCB still 17mm.
From the pics I count A few less components, but I might have missed something the pics don’t show.
I have built several of these drivers now with problems, my fault of coarse. The design is good it’s the small components that makes bad connections or shorts so hard to spot. What kind of problem are you seeing?

The most recent one, I didn’t have much difference in modes. That’s the one that was reporting 19 amps on the 87V setup for the XHP35.2. The modes were there, the output didn’t change much from mode to mode when switched. After a few hours of trying to figuring out what was going on, I tested R11 which was reporting a very low resistance. Unsoldered the resistor and it read fine off the PCB. Checked the pads and saw a very low resistance. I chased it back to the mp3431 and saw that pin 5 and 6 (FB and AGND) looked like the were touching. Applied some Amtech NC-559 flux and hit it with a fine tip soldering iron. The solder jumped right apart and flowed to each pin, amazing flux.
Now the modes work fine.

I did get the UT210E clamp meter yesterday. This is after I fixed the short at pin 5 and 6. The UT reports 16 amps and 2600 lumens at start up running the XHP35.2 and the 87V reports close to the same. I actually ran the 87V homemade thick leads threw the UT to get the reading. Before I found the short it reported 19 amps and 2800 lumens at start up. I can’t get it to run a 19 amps again, so I’m guessing the short had something to do with that.

Yes, my board is my own design and it is 17mm. However, the boost circuit is entirely based on loneoceans schematics. I use the same boost IC, op-amp and component values. He hasn’t made the schematics public but was kind enough to send me them on request although he has not finalized them.

I made my own because I want to use my 1634 firmware, I don’t want to go back to the 841. And I really hate working with 0402 so I attempted to make it with 0603 instead. The main differences with the layout is that my 1206 caps are on the battery side and the MCU is on inductor side. I have a few less components because I don’t use an external temp sensor, E-switch pull ups, reset pin pull up and OTC cap. I did forget to add an input cap to the op-amp though, so I might be getting noise. I can add one from that pin to GND ring though, the op-amp is orientated that way on my board.

The issue I’m having as that the output as varying up and down although I’m increasing PWM duty cycle. I have to hook this driver up to an oscilloscope and really check everything before I start replacing components. It will force me to learn a few things about this boost circuit design. I’ll also have to check everything with a magnifying glass and maybe use some flux here and there.

The thing with making my own board is that I can’t really say if any issues I have is due to layout, because layout is important. I’ve tried to follow MP3431 layout guidelines, and tried to stick to loneoceans layout, but by using 0603 and larger MCU I have had to make some compromises.

Good luck with the problem solving Mike.

Can I ask you EE guys a couple of off topic MOSFET questions real quick? You all seem to know your stuff and I’m just barely learning.

1. Are the majority of MOSFETs we use in flashlights N channel?

2. All N channel normally resist flow between the source and drain, correct?

3. Then your P channel always allows flow, correct? I think this is the big difference in them.

4. Providing a positive signal to the gate of an N channel allows flow and on a P channel it stops flow, correct?

5. Lastly, are the gate signals always a positive voltage or can some MOSFETs be triggered with a ground signal?

Thanks in advance for any help.

1. Yes
2. No, you can sub-divide the n- and p-channel MOSFETs into “enhancement-mode” (normally-off) and “depletion-mode” (normally-on) categories (these 4 types have their own schematic symbols). Enhancement-n-channel resists flow (hence the name normally-off), and is the most-often used type of MOSFET. And usually when people talk about MOSFETs, they usually mean a normally-off MOSFET, if they don’t specifically say it’s a normally-on type (since they’re not that often used)
3. That’s what depletion-mode MOSFETs do. A p-channel-enh. MOSFET (which you are reffering to) normally stops current flow the same as a n-channel-enh. Just the “activation method” to let current flow is the other way around. Instead of positive voltage compared to Source pin (positive V_GS) (that’s what a n channel needs), for a p-channel you need a negative voltage compared to Source pin (negative V_GS) to let curent flow.
4. See answer no. 3
5. I’d like to clarify some things here: MOSFETs generally don’t know what a positive or negative voltage is. They have no reference (ground) to be able to tell positive and negative apart. This is just us, that defined a specific voltage potential as “ground”. That way it’s easier for us, and the calculations. What MOSFETs however do know, is “more positive/less negative”, and “less positive/more negative” (the words separated with the Slash are equivalent). It compares the the Gate potential to the Source potential, and acts accordingly.
So to answer the question: MOSFETs don’t care whether the Gate signal is positive or negative, it depends on the combination at the Gate and Source. So yes, all MOSFETs can be triggered with a ground signal.

To easily explain depletion Mosfets: Think that they are like enhancement Mosfets, but a bias is already at the Gate pin, that turns them already on. So you need to go in the other direction (in terms of voltage) to overcome the bias to turn them off again.

And just to avoid some misunderstanding, in short:
(V_GS is voltage between Gate and Source. “Positive” means Gate more positive than Source, “negative” means Gate more negative than Source”)

n-channel-enhancement Mosfet:
normally-off, positive V_GS to turn on

p-channel-enhancement Mosfet:
normally-off, negative V_GS to turn on

n-channel-depletion Mosfet:
normally-on, negative V_GS to turn off

p-channel-depletion Mosfet:
normally-on, positive V_GS to turn off

Okay, I was hoping it would be a bit simpler, but I guess I need to keep studying. :smiley:

This might help a little. https://www.quora.com/When-is-it-good-to-use-N-MOSFET-and-when-do-you-use-P-MOSFET

I wonder….
I see more and more enquires about high voltage drivers. Hyperboost is the only solution out there.
I see that the IC here is rated to 90V output.
What would it take to turn GXB172 to a high voltage driver?

It is limited due to the IC it uses. It has a max voltage of ~16V IIRC.

So an entirely different IC would be needed and that basically means a whole new driver.

Ouch, I see that I mixed up different products. Yes, 16V limit. That kills the idea. Thank you for setting me straight!


Were you planning to use a COB?

As of now I don’t have any such plans. Now that you’re saying it - a flooder with 3000 lm CRI97 COB would be interesting. :wink: Though definitely out of my skills range.
I think I’ve seen at least 4 inquires about it in the past quarter - and that’s it.

Glad to see others have gotten this working, too! :slight_smile:

Thus far, I’ve built a total of 4 of these—two of the original Rev A and two more of the Rev A2. Sadly, I managed to fry one of the original Rev A boards, so I only have 3 operational right now. I am rather happy with them, but still would like to hack on the firmware a bit.

When I get a moment, I’ll try to get some more pictures of the new builds, along with some measurements. However, I wanted to check in here and ask a question, as my fifth build is currently having some issues: after I power it up, it blinks the LED (at lowish power) 4 times before turning off. My guess is that communication to the temperature sensor isn’t working? But wondering if anyone else ran into the problem / how to solve it.

I’ve got some of the 20mm boards (finally!), and will be doing some builds of those with some new S11 hosts from MTN.

(And yeah, I have had trouble getting my hands on the 47uF 25V recommended caps; 10V and 16V are fine for 6V and 9V operation, but 12V is too little margin. Managed to get a few from Mouser but they are since out of stock.)

It’s been awhile back but I believe the very first one I built had the problem you described. I had used a small amount of solder paste on the 4 small pads and you can imagine what that did when reflowed with hot air with the pads being so small. I tried reflowing it again a few times and never did get it to work properly. I finally reflowed it off and cleaned the pads of any solder, used a brand new temp sensor with just flux on the pads and reflowed. That fixed it. I’m pretty sure it gave me the same 4 blinks then off until I reflowed the new temp sensor on with just flux. I would try replacing the temp sensor or try reflowing the installed one again, maybe giving it a small tap on the top of the head when the solder reflows to get all 4 legs seated. I know it’s a pain being so small but there’s not much else you could do besides replacing it and try again.

The last 47uF 25v caps I purchased came from aliexpress. They were considerable cheaper for the amount I received. They may not be of the same quality and I haven’t used any yet. But I did measure a few at 40 to 42uF. I do need to try out a few before I could recommend them. If they can hold up under the voltage they should be fine.

Let us know if this fixes the problem. :+1:

Can you connect two small wires and let it float or sit somewhere else?

Might want to tone down the cussing, it is not allowed on this site.

That said, having been working off and on with another member for a driver like this, I can tell you that getting this working at all is WAY harder then it sounds.

LO did an amazing job to even get this driver functioning at all.

I also spent well over $100 on components for the testing and prototyping of drivers based on this IC :person_facepalming:

Sorry, deleted comments I shouldn’t have posted without giving myself time to cool off and think clearly (and phrase things far more politely).

:+1: don’t forget it’s just a hobby

I wonder if more people has build this driver for themself? Maybe with firmware avalible for all, we can create some improvement which people have requested, but I do not have enough skill to make modification with open firmware and currently I am happy with basic firmware.