I haven't tried to keep track of that. I know some people have used it to drive xml's using it in it's stock configuration (7ish amps). It's a popular UF-T90 mod. Driving an xml/xml2 over 7 amps is touchy business with any driver. I did a quick search and saw a couple examples of driving xml's in other lights or just testing of 7 amps and less.:
Interesting. Thanks for the links, that’s the kind of thing I needed. So, while I’m confident about the PWM voltage not being the source of the problem… maybe it would have been better if DBCstm could have tested the stock driver on an XM-L/L2 before doing the ATtiny13A mod. My money is on the idea that he just got a bum driver!
I got 2 and have had the same issue with both. The issue is in the driver giving too much Voltage to the emitter and frying it when using larger wires. Richard has been having the same issue I’ve had and is working on solving it. He’s burned up 10 LED’s to my 5 or 6. So now I know it’s not just me.
So, apparently putting 20 ga wires on it lets the buck converter run the Voltage up too high.
So you’re saying that with the stock wires it doesn’t zap XM-L’s, just once you bump to a heavier wire gauge? (just verifying!)
That's right. I had one driver that I got away with the thick wires on...The subsequent ones have been blowing LEDs.
Bummer. Starting to sound like this is an MT-G2 emitter only driver. Thank you for the info guys. I was just about to build a light with this driver and xml2's. Need to go another route, it seems.
I will post some more details soon, but all it needs preliminarily is a little output capacitance. 22uF ceramic is enough to keep it from blowing LEDs with the factory sense resistors.
I also tried swapping FETs, diodes, and adding more inductance, none of which seemed to help at all. I was surprised that adding more inductance didn't work.
I will see how far I can push it with extra capacitance. Unfortunately I don't have an oscilloscope so I can only tell whether or not the voltage is staying within the limits of an XM-L2 but I suppose for our purposes we don't need a perfectly clean output. 
Good work RMM. It seems that an inexpensive scope might pay dividends if you are burning up a lot of LEDs in your testing? Just FYI, the PC based one comfychair is using is $75 shipped from the US.
I do have a scope, although I only get one channel. It seems that my QX5241 driver zapps LEDs at 6A, based on one potentially flawed test. I’ll get some more caps in hand and take a look at that on the scope ASAP… starting at 4A of course ;-).
Just a another quick update:
With two 25v 22uF ceramics on the output I can run 50 and 68 ohm sense resistors together with no issues, which delivers over 8A to the emitter with 18 AWG wires. My TK61 is pushing over 2000 lumens OTF now!
Sometimes the simple solutions are the best ones.
I know you are always pressed for time. Would it be possible for you to grab the 4 values required for an efficiency calculation? Vin/Vout Iin/Iout
Either way, thanks for the update!
I spend much time at the law office these days! If I remember correctly, it was pulling about 5A on the input for over 8A on the output... sorry but I don't remember the exact numbers but I am going to be building some more this week. I'm guessing that efficiency is around the 85% mark when it is run full bore.
I think I am going to order an oscilloscope. There have been a few things that I have been able to pin down by trial and error and lots of online searching, but it could definitely be a time saver (and time is what I am usually short on.)
In a few more weeks I will be done with my law office/internship assignments and back to regular school, which interestingly enough gives me more time experiment, list, etc. I thought I would have more time this summer but I have had significantly less because I decided to take on the second job along with the first.
RMM wrote:
With two 25v 22uF ceramics on the output I can run 50 and 68 ohm sense resistors together with no issues, which delivers over 8A to the emitter with 18 AWG wires. My TK61 is pushing over 2000 lumens OTF now!
Sweet! Congrats and thanks for the info.
EDIT: Please let me know if you start selling modded versions of these drivers. I will put a link in the OP.
They don’t have the same pinout, that much we can be certain of. I’m moving this conversation back into your thread though, this info is more useful there!
Based on the photos in RaceR86’s post #67 in this thread I’d say we’re almost certainly dealing with QX9920. If that's the case, I'm starting to see why they've got all those resistors around the PWM line. They appear to be abusing the EN (enable) pin rather than using the TOFF (PWM) pin. I wonder why?
QX5241
1. CSN
2. DIM (PWM)
3. VIN
4. Vcc (regulated output for MCU/etc)
5. DRV (gate)
6. VSS (GND)
Mystery chip
1. DRV (gate)
2. VIN oops, GND!
3. (PWM)
4. VDD (from zener W8 by way of S4 RP protection diode)
5. ?
6. CSN
QX9920 (marked with LEDA & date code probably)
1. DRV
2. VSS (GND)
3. EN (Chip Enable)
4. VDD (needs regulated VIN)
5. TOFF (PWM)
6. CS (CSN)
Darn. Thank you for all that good info wight.
I actually have the QX5241 chips because I ordered them when you first started your QX5241 thread. Seems like too much trouble to hard wire it. I'll try to find some of those QX9920's and hope for the best.
I've been meaning to catch up on your QX99205241 thread and also on Ohaya's LM's Driver thread that you have been helping with.
No problem.
I definitely wasn’t suggesting an attempt to hookup the QX5241 in place of the QX9920 - I just listed the pinouts to illustrate my point. I’m not saying it can’t be done, but we’ve got enough hurdles as it is!
We should be in shape for you to use up a couple of those faith-purchased QX5241’s soon. Maybe not in 17mm yet, but at least in 20mm. Do you also have SO8/Power-SO8/LFPAK56/whatever N-channel FETs? If so we may as well get you hooked up with some PCBs so you can start blowing stuff up.
I think these may be the cheapest QX9920 on AliExpress in QTY=10 or less at ~$5/shipped for 10:
http://www.aliexpress.com/item/10PCS-QX9920-9920/1068294410.html
+1
Not sure. I only have a few different type of N-channels. I'll check and get back to you.
Ordered set of those QX9920's. I'll report back how they work out.
I just tried Richards cap solution, but I didn’t change my resistor set-up that I was using with the Luminus SST-50. Which proved to be too much for the Cree. 8.23A at the emitter on the Luminus SST-50, completely de-domed and naked as a JayBird. I have a R068 and R140 along with an R200 and R140. This should be R029419 which is a wee bit less than stocks R034.
Working on creating a base for the reflector to sit into so it stays centered when I tighten the bezel. Wish I had more Sugru…
I have spent more time working with this driver over the past few weeks than I care to admit (along with killing over 25 LEDs!!!!)
These are a few of my current observations:
1. The stock driver with the stock MCU and sense resistors (stock everything) on the highest level produces a voltage peak of around 4.22v, valley of around 3.26v, for a whopping 0.96v of ripple! Most XM-L2s seem to die at around 4.15V+ so the stock driver is too much for good input cells and thick wires.
2. The stock inductor seems to saturate at 100%. You can vary the PWM levels and sense resistors and the output will be fairly smooth and controlled until around 6A output, after which point things get out of control in a hurry. A larger inductor (more saturation capacity and uH) smooths things out a LOT at higher current levels, but makes the lower output levels have more ripple.
3. Adding some additional INPUT capacitance helps smooth things out at the higher drive levels. I suspect that the driver attempts to overcompensate for the input ripple.
4. Extra output capacitance helps a little bit, but not enough to keep from blowing XM-L2s unless you add a combination of ceramics and a LARGE (1000uF) electrolytic on top of that. This is just masking the underlying issues (toroid too small; too much ripple)
5. Fast 19.1K PWM works great coming from the attiny13a. I seem to get the best and smoothest results using this then setting the peak PWM level to around 200 instead of 255 (full on.) The buck IC seems to like this better than going 100%...you get around 95% of the 255 output but the output ripple is much lower. The buck IC seems to react much differently to full on PWM vs almost full on PWM. If you need more, just reduce input resistance.
6. You can piggyback or switch out the flyback diode if you want to reduce heat a little bit.
7. The 70N02 works as a replacement for the stock FET and it also seems to reduce heat generated by the driver (probably a much lower on resistance and/or faster switching time.)
A few takeaway lessons:
i. The stock driver will probably blow domed XM-L2s and will certainly blow dedomed XM-L2s (they seem to take a bit less overvoltage to blow). You can possibly get away with running it with an XM-L2 stock with 24AWG or smaller leads. The driver blows LEDs due to excessive voltage spikes not due to excessive current.
ii. If you want a good reliable buck driver without changing a lot of things, just add more resistance to the limiting bank. If you get it down to around 5A on the output it works great without any other driver changes.
iii. The quickest and easiest way to get the driver smoothed out at higher drive levels (6A+) is to add a larger inductor, add some input capacitance, and limit PWM to around 200 with fast PWM. The larger inductor and extra capacitors do add size to the driver so this won't work for some setups.
iv. If you want to reduce heat at the higher drive levels (7A+), swap out the FET and piggyback another large diode onto the flyback. The next biggest heat producer are the big limiting resistors but there is no way to get around that loss with this driver.
v. On the scope, adding modest amounts of output capacitance don't seem to help a lot. For higher drive currents, focus your efforts first on the inductor then on the input capacitance. If you need a bit more after that then you can add some ceramics to the output (but I doubt you will need it.)
^ Wow, 25 LED's lost in the cause for improving performance. Talk about sacrifice. Thank you for all that and the resulting info. The ones I currently have will just have to be for lower current xml2 or higher current MT-G2 as I don't have the electronics knowledge or components you discuss.
Do you know at this point if you plan on selling these drivers?