Which IC was that?
The Texas Buck should work as a base for a Q8 buck driver, although it would not put out as much total power as the Q8 does now. Although I think we have found some better PFET’s to use compared to the one in the design.
The only practical way to make a buck driver work in the Q8 is to rewire the cells to be in 4S. There is simply not enough voltage overhead and you need too much current to make a 1S buck drive practical.
I used the ISL8117 in a 4S configuration and it should be able to output 20A.
Edit: But with that controller you need an inductor with 10uH (limiting the current capability), but now I found a controller that needs 4.7uH (with the same frequency and more efficiency, and the frequency is pretty low for less switching losses).
Hmm, a quick glance at the ISL8117 looks really interesting. I really like what I saw, that indeed would seem to make a good IC for the Q8, it is even small enough that it could fit on some smaller drivers.
Whats the new IC you found?
I am actually working on another project where we are trying to drive 15A+ on a buck so a new option would be nice.
The other one I found is an LM5145/LM25145. They both are nearly the same controller, the LM5145 has a higher maximum input voltage: 75V compared to 42V at the LM25145. Everything else is the same.
I stand corrected, I found it now… Pretty odd, shouldn’t matter what EU country they send to.
Well, I’ve been using them in one of my headlamp projects and they work alright, but the ones I have don’t draw 330mA, the consistently draw 250mA. I had to check if I got the wrong ones, but they are marked as 330mA versions. Other than that they same to be very reliable. I’ll be trying to get the 350mA versions next time.
And what IC did you choose for your project, and who is working on it with you?
So if I understand correctly one could make a driver working on 6V input and with the number of these chips control the output?
Like a 8*7135 for XPLhi, we could make a n*chip for XHP70.2?
I’ve used them for a 2S driver for the 6V MT-G2 here: Mod/build: MT-G2 & dual Nichia 219C headlamp
They are basically 7135s rated for 12V. Maybe they can handle a little more. I might give a go at seeing weather they can handle 16V for a 4S configuration (XHP-35 HI), but a buck driver would probably be a better solution.
Yeah, The Miller, that’s the idea. Up above Mike C said, “For 2S lights the A705NGT might be of interest. They are basically 7135s that are rated for 12V.”
This is getting me excited for all the Q8 modding to come.
Del and I have been working on a project for an un-named manufacture for an un-named light that would require over 30A of power. We settled on 2x 15A drivers in parallel as the best method to reach that.
We have been working with the LM3404 right now, it is a little undersized but should work with the right PFET. The larger options we found all had issues that made them impractical for flashlight use.
The ISL8117 looks interesting though, I am going to show that to Del and see what he thinks. We had not seen that one yet.
Seems like we saw the LM25145 at one point but I will have to check. We have looked at too many to keep track of lol.
LM3404? This IC has an integrated FET. Do you mean the LM3409 instead?
Opps, sorry, yeah, the LM3409.
what are your goals on input and output current/voltage ripple?
The overall setup is 6S6P input with an 18V LED output with a total current draw of ~30A.
Ripple should be as low as is practical, we are working on the rest of the setup and going to kind of see where the ripple ends up. Looking like it should be around .25A or less from early calculations IIRC. The real issue has been finding a PFET that will work.
The project has been on hold for a little while now while the manufacture tries to find a PFET that they can source that would work.
6S6P? Probably need a backpack for that 
Lets just say that this is not a light that will be an EDC choice lol.
Seeing how TomE gets 27 klm with triple XHP70.2 in MT03 I really wish to do a similar thing with Q8.
Having quad LEDs it should certainly do 30k. It would be even better when running 12v. But there’s no XHP70.2 PCB and no suitable FET+linear drivers……
I don’t think you realize how hot the Q8 would get at 30k lumens. Going off of past numbers for the XHP70.2 at those kinds of outputs.
You are looking at around 120 watts per LED.
So around 480W total output.
To put things into perspective my SRK mods that are doing a mere ~150-200W get hot in about 30-45 seconds (think BLF A6). With 2-3x the heat you are literally talking about 10-20 seconds to get hot.
In addition to this, most cells can not support that much output.
Most cells are only rated for a max of 20A with a few reaching 25A. You would need cells able to support ~35A each to power this safely.
So while yes, it could technically be done. Is it really worth it? That is up to each persons wallet I suppose.
I can say I rarely use my 8x xhp50 SRK as it simply gets hot too fast to be useful, even if it makes 17k lumens. I prefer my 10-13k lumen SRK’s that are much more reasonable.
I have never used anything like that, so maybe I don’t realize. But it sounds like my D4’s bigger brother. I have the hottest variant, use it with VTC6 and ordered VTC5A because I can’t have enough.
My novice thoughts are that using 4x XHP50s is about as much light as you can get out of the Q8 practically. I got my first XHP50.2 light and it does about 2000~ lumens from 6-8amps and isn’t busting a sweat in terms of heat during extended running. In the long-term I do not see my Q8 being stock forever(not that anything is wrong with it), but I am on a unending quest for more lumens. Though 20A per cell in a 4x 18650 light doesn’t sound unappealing… I’m not ready to put that many watts in my hand just yet.