The Texas Buck driver series, Q8 / Skyray King 2S/4S buck driver RELEASED!

Percent power loss for the 22 and 15 uh inductors and the percent inductor ripple current:

2S 1S
1 MHz 300khz 1 MHz 300khz
Value High P Low P High P Low P High P Low P High P Low P
15 uH 14.4mOhm P_L % 2.67 0.40 3.17 1.82 6.44 0.72 7.10 1.79
delta I_L % 2.84 68.06 9.45 226.85 1.54 23.09 5.13 76.97
22 uH 26.5 mOhm P_L % 4.79 0.52 5.41 1.92 11.70 1.13 12.51 2.30
delta I_L % 1.93 46.40 6.44 154.67 1.05 15.74 3.50 52.48


Diode and switching losses bring that closer to 20% for 1S high power, plus whatever losses I haven't considered.

High power there means 15A, ~53W for the 1S and is 12A ~84W for 2S. Low power is 3.5W total in all cases.

1S is tough. In non-shielded inductors or in 22mm footprints, there are considerably lower resistance options available though.

3.5W is discontinuous mode at 15uH 2S, but 1Mhz keeps it alive, and maybe this fancy IC will anyway.

All very good info. It is possible to fit a 22mm inductor onto the Q8 driver but obviously any smaller drivers will not handle that.

While I want it able to handle 15A I am also realistic that we will most likely be overdriving something to reach that.

I am not sure what you mean when you say that rewiring the Q8 MCPCB would be easy? More like impossible? Now you could use individual stars as a replacement but that kinda of ruins the point of the nice mcpcb. It is an option for the extreme among us though.

Honestly my biggest goal is as an XHP35 driver with 4s input and 4s output and able to provide the ~3 amps per LED that they can handle with a low enough ripple that they don’t die.

If we can reach those goals with a bit of headroom it should handle anything else we may desire. XHP50’s would be best run with an FET+2 for the amount of power they need, same for the 3V emitter options. This is why I made the Texas Avengers for those setups.

Now I do plan to make smaller versions of this driver for other lights but it will obviously have much lower current needs as well. Just not sure what lights would be able to use them besides things like the L6.

First Cap footprints: Main cap, 35 to 50V rating, requires 1210 (or 1206) specifically this:

http://www.digikey.com/product-detail/en/samsung-electro-mechanics-america-inc/CL31B106KBHNNNE/1276-6767-1-ND

Maybe use the same cap before the FET.

If you can fit 22mm on the Q8 I definitely would. You can bring 26mOhm down to 7 (BIG efficiency savings) and get a full 15A rating!

http://www.digikey.com/product-detail/en/wurth-electronics-inc/74435582200/732-4237-6-ND

Worry about smaller ones for smaller drivers. We’ve found a few, easy to come back to them. Further I would add through holes to allow optionally mounting unshielded toroid inductors unless there’s really no place for them to exist. It will give options for testing/learning/improving and that might help down the road.

It’s not quite true that 2S is a slam dunk after doing 4p. Yes I^2R and IVf loss/heat get easier, but inductor ripple is maximum at 50% duty factor, about 3x worse than for 25% duty factor, so you enter discontinuous mode earlier and either need to start pwm earlier (not so bad), or you need more inductance or higher frequency, either probably at the expense of some losses for the same footprint, but cheaper than the same game at 1S. Probably PWM earlier is as good of a solution.

Like you, I don’t see output ripple being a big issue. As I interpret the capactor dissipation factors, I’m getting values of next to nothing (1 mOhm) for ESR at 300khz. I’m inclined to stick 20mOhm in the math just in case, which still leaves output ripple under 2%, actually a tiny fraction of that at high power. The hard part here is likely good connections and traces.

Anyway, Rufus, ripple kills LED’s? and PWM doesn’t? I don’t believe it. 6A modes with 10% current ripple kills LEDs. That’s not exactly the same as “ripple kills led’s”. Of course we're talking about ripple voltage though, and that translates to more in current, still it's overvoltage/current that kills it.

As far as PWM, actually it probably doesn’t need another FET at all, just use the PWM port on the IC as it was designed. You just need one trace and a spare mcu pin, no component. Then it's up to software.

Ok, making 2S is probably somewhere between easy and impossible, I haven't looked. You should be able to cut traces (no?) and solder onto the top connections of the LED’s (after scraping the coating). Apparently that’s a pretty big pain after they are already on a heat sink. Or just sand off the trace coverlays and solder to the board. This is really too bad though. Why not have jumpers/solder pads on the LED boards? Is it really too late to do that? I doubt there can be a more capable driver with present tech, than a 4s to 2s buck. You can get melt-down modes, and suck the life out of the batteries to maintain intermediate modes, although moonlight will probably end up slightly more efficient on the 1S. so like 500 hours instead of 350.

I just started searching for schottkys. I way underestimated Vf. At 0.55V (ok 0.45 at 15A, less if it warms up well) ... schottky losses are looking very big in 1S output, about 9.5% vs 3.1 in 2S. I did find a synchronous IC that could work (bypassing this loss), but it was constant voltage, divider style, only. Might be dimmable with some hack.

There are 10uf caps available in 0805 as well, I have some that I ordered for C1 at some point.

22mm should be able to fit but would leave very little extra space for other components so we need to make sure they are all in order first.

Far as 1s vs 2s vs 4s. In the Q8 (what this driver is really meant for), it comes stock with 4x 3535 LED’s in parallel and another 4x 5050 led pads as optional, also in parallel (assuming that Thorfire uses our design).

The MCPCB design is setup for parallel only and switching it would be much harder then simply installing new DTP stars.

So with the setup it comes with the 1S 3V emitters it comes with are best driven by an FET as they will be needing 16-20 amps of current, while this buck driver could do that it would be a lot of extra cost and effort for very little gains unless the LED’s were rewired in series with individual stars, that is not worth it except to the extreme modders.

The 5050 pads are basically for XHP50’s, they are once again best driven by an FET driver due to the fact they could easily use 20+ amps. Once again this buck driver would work but if max light output is your goal we all know that the FET will win.

Now the last major mod idea is XHP35’s, they are obviously 4S voltage only and can not be driven with an FET due to the fact they like to fry like that. So that is where this buck driver comes in, it is to allow XPH35’s to be dropped into a Q8 for a high CRI 8000+ lumen monster of a light without a donut hole issue.

So 4s input to 4s output is the primary concern, the others are great to play with later and if it works with 4s to 4s it should work with any of them given component changes. The XHP35 is the only setup that requires a buck driver, the others would just be for the extreme modders that want the very best, even if they are spending as much on the driver as the light itself. Although most of them will want an FET anyways.

I had thought the PWM port on the IC should work but figured I had missed something.

I'm sorry, yeah, I misread (maybe a few times) as 4p being primary concern I see (didn't really know about xhp35's and hadn't looked yet). Well I still think 4s to 1s is nice even if 2s might be "impossible". Max output is not all that matters. The buck will give you controlled output much longer (in anything other than 4s to 4s at least). Can that light really sustain more than 50W or power without burning your hand? Turbo shine is neat, but for long use at say 30 to 50 W without battery sag getting in the way, a buck still seems useful. I'll have to get my hands on the light. It's hard for me to imagine how it could be so hard. Worst case you resolder the LED's with their bottom pads grounded down and use the top contacts to connect wires, unless their is really no space for a wire. Mildly complex mod but so is assembling one of these drivers.

Anyway, I will add 4s to my scenarios. I put in component specs and get out performance specs for as many use cases as I want. Still, all these scenarios have different difficulties. I don't think any one makes all the rest optimized. In 4S the diode loss won't matter at all for example, in 4:1 it's a big deal.

As for the caps, yes, I've found many in 0805. I didn't find any with high voltage rating. I guess they should be 30V minimum, but I definitely could have missed them.

This is the proposed MCPCB for the Q8, as you can see it would be very difficult to convert to series, although not impossible. That said the work to convert would be more then simply dropping in new stars, which is what I would do if converting but that is something I would only do for a show light.

The buck does not have to run at 4s, it can also be run at 2s2p levels.

Naturally the light will not handle that level of output long term, heck even stock it won’t handle turbo long term. We don’t care about that here at BLF, we want usable modes for using the light and then turbo modes for play time. lol

Driving 1s or 2s LED’s is nice but honestly unless they are in series you won’t gain a whole lot over the Texas Avenger driver I already have for the Q8 with the bank of 7135’s. Not nearly enough to be worth the price or effort IMHO.

Now if you convert the LED’s to series as well, then things get more interesting but that is far too much work unless going for max possible lumens (not something I chase much anymore).

Now the smaller versions of this driver will only need to worry about the ~6 amp range which is much more reasonable.

I have to find a place to post pics. My first idea goes like this. Isolate the cathode with a vertical cut to their left. If cutting from top to bottom, stop when you hit anode trace and turn right, cutting across the two through holes and stopping above led 3.

You can mount led 1 and 3 backwards and jumper the cathode to the area north of led pad 7.

That requires reflow. With just a bit more cutting (basically continue the horizontal cut out to both edges) and two jumpers you can do it without reflow. All this could easily be accomplished with a few cuts in the trace, zero ohm resitors and/or an extra solder pad prior that would allow reconfiguration. It's really unfortunate in a light intended to be moddable.

2S isn't just about max lumens. It's about keeping say 2A per led (or whatever it can sustain) from being affected fairly quickly by voltage sag. It gives you a setup where light performance has nothing to do with the battery voltage sag/depeleting, so long as it's capable of putting out the power required. But yes, you get max lumens too, so everyobody should love it. Anyway, I didn't understand about xph35's and I should have stopped to understand what you were saying there. I will try to post a pic later.

That's probably not even the most clever way (almost the least) just first things I saw. I think can get a solution with either no jumpers, only cutting, or certainly can get one with no reversing of led's and probably still only requiring one jumper. I'll try post pics later.

Bettter yet, you can use the extra led pads for the jumper(s). It might be possible to make this fully reversible/reconfigurable just by re-configuring 0-ohm leds on thee extra pads. Splitting the wire pads gives even more options. Now it's like a game. Is there a way to cut traces so that xml's can then be configured in 4p, 2s or 4s only by jumping large led pads, and changing wire connection points, without even resoldering leds? The thermal sensors might get in the way, not quite sure how they are wired.

Oh, you can mod the MCPCB to work in series, anything CAN be done. I said it was easier to install individual stars and I still say that is the case. With stars you simply install them, line them up and glue them down. All bolt in parts with no custom work needed. Even for me I prefer bolt in whenever possible. Why makes things harder then they have to be.

Personally I would have preferred the light be setup for 4s LED’s run by 4S cells from the start (maybe 2s2p LED’s). The overwhelming majority said they wanted 4s cells and LEDs though so that is what we have at this point.

Got to work with what we have.

To me this all seems MUCH easier than assembling a driver (which you still have to do but...) and it's quite a bit cheaper and faster than ordering new stars. If a few cuts in traces, and existing jumper points (the extra led pads, or just add proper jumper pads) can make this reconfigurable is it really too late to push it through?

(are they heat sink pads case grounded? do they need to be avoided electrically?)

Yes, the MCPCB is DTP. Like I said it could be converted but I personally hate cutting traces, I have always had massive issues getting a clean cut that doesn’t short out.

The $4 for new stars would be well worth the cost for me but to each their own.

Solved all that:

http://imgur.com/gallery/ebS7c (well solved in theory, I'd have to learn dip trace to actually solve it)

4p as shown, positive is always to the left (or negative if you prefer).

Can do 4p, 2s, or 4s. No cutting, only jumpers (4s requires jumpering two of the wire pads, although there is room to route a trace for a zero-ohm resistor instead for that too, but jumping the wire pads seems ok). LED's do not need to be reversed. This should work as a stock board. (I deteted the thermistors because they were in my way at the time, but this is just a concept version obviously)

I had considered this, actually had a design half made up for something like this but decided against it as people would complain that the traces were not big enough.

If Miller says he is ok with trying to change it at this point I can finish my first design and see what the Q8 guys think of it.

Either way it doesn’t effect this driver much. The goal is to design it for overkill and then work backwards for smaller versions. I figure I would like to work down to at least a 26mm and maybe get a 20mm if possible since the mtnmax is not available in that size. Although that would be limited to the tiny13 which is not a great option but thats for a later design.

What's wrong with the one above? The places where traces are narrow, it's obvious how to improve it, just didn't for the concept drawing. Random addressing is fine, but that plus laying it out for short jumpers for the most used paths without ever needing LED reversal is a bit more of a trick. I did try to keep the central pad/hole design the way it was because I didn't know the constraints. If I could put pads anywhere I want, traces get a little better yet, but I'd still do it like this basically.

Anyway, if I inspired movement on it, that's great to me.

There is nothing wrong with it, but if going for a fully customizable board, might as well go all out IMHO. I tossed together another version and posted it in the Q8 thread that allows any setup you could want using jumpers.

The issue is practicality of thorfire actually using it or any of our designs.

Get it to production. There are a number of us that wish it………………when the Q8 is ready. Hope we get an update from TH soon!

Edit.. moved my comments there. This is was buck driver thread.