RMM, it sounds like you are referring to frequency rather than duty cycle.
It’s definitely a cap, it’s the TOFF cap connected to pin5. Reference the datasheet.
Good pic & soldering ohaya. I looked at the picture before reading what you wrote and I was caught off guard by the R200 - it blended right in with the rest of the driver.
You could have different input resistors and with a different duty cycle maintain the same output current with the same switching frequency and increased duty cycle, right? Or am I mistaken? (assuming you aren't maxed out already on duty cycle)
That sounds correct to me.
I suppose that's all theoretical, but good to know I'm not too far off the mark! 
Heh, it’s definitely all theoretical to me. That said, I still don’t have a firm grasp on exactly what that TOFF cap does. It seems clear that they intend for you to change it’s value based on some design parameter… I just don’t understand things well enough. I’ve mentioned that before of course. Maybe someday, in the future, I’ll get my hands on a few QX9920 drivers and some motivation & time and watch it with my scope as we swap in a few different values. I haven’t looked over that section of the datasheet recently, but there are at least a few tiny details, so if you haven’t looked at the Google Translate of it I suggest you do so (side by side with the Chinese original so you can see the pictures).
OK. I killed my 1st one today, in a 2x14500 light with 3 x xp-g2. This was with 2 r200 stacked on the original r100.
Upon review, I found one end of the 3912 schottky diode melted.
I replaced that with a new 5amp one I had for the LM driver, but after that I don’t have modes anymore… just ‘high’:)…
Was it OK to use that replacement diode?
If so, what else would cause loss of modes?
Edit: The 3 emitters are in parallel. The 2 14500s are in series.
The replacement diode probably didn’t cause your modes problem, although I continue to caution you that you should stay below the rating, not at or above the rating.
Maybe the modes chip got damaged by some kind of spike when the diode died.
How low is your battery voltage getting on ‘high’?
Wight,
The replacement diode was like 20 or 30V @5amps (I got a couple of different ones, but I think the one I swapped in was 30V @ 5 amps). I hear you, and I probably should have been more conservative with the stacked resistors, and may try to remove one of the R200s, but anyway...
I'll have to check the battery voltage tomorrow, but I was just ohming around, and noticed that the emitter + lead shorts to the battery + (i.e., to the spring on the battery side of the driver). Is that "normal" and "ok" for this type of buck driver, or is it wrong (and I need to figure out what's shorting)? Thanks, Jim
A couple of things for the record:
1) I ohmed another LD-44 board, and found that there was continuity from the emitter + to the battery +, so I guess that that is “normal”
2) I found that there wasn’t good conductivity from the body of the pill to the “-”. I had originally press-fitted the LD-44 into the pill without soldering, so I tried to do a solder bridge from the pill to the LD-44 ground ring. I think I was successful, because…
3) I now have lights, and, better yet, have modes again!! With 1 14500 + a dummy 14500, tailcap on high mode is ~1.43 amps. I’m still trying to decide if I should try 2 x 14500 again :(…
4) At bottom line, I don’t know why the modes weren’t working earlier, but I’m glad that they’re back…
5) I also tried some tests, shorting the “0”, “1”, and “3” pads to negative. I couldn’t see any behavior difference…
1. Yeah, LED+ having continuity to BAT+ sounds fine.
2. Sounds good.
3. Unless I miss my mark…. With 1x14500 @ 1.43A input you are certainly limiting your output to somewhere under 2A. That’s not even a happy medium, the stock driver could do that I think?
4. meh
5. If you wanted to you could do some quick tests to ohm out where 0/1/3 go on the top. Most of them probably connect to the 00VM chip. I don’t know if they need to be shorted to each other, pulled high (BAT), or pulled low (BAT-). You could test the voltage between 0/1/3 and GND while the driver had power on it. If they go high (BAT) then they probably need to be pulled low to get something to happen. Otherwise they might need to be shorted together or pulled high to get something to happen.
I will try to ohm out the 0/1/3 pads later, but I think I’ve found why the modes weren’t working earlier.
I found that one of the 14500s I have, a protected TF flame (ok sorry, but I have several, and it’s just this one), when I use it in this light (and also tried in other lights, same thing), I get only a kind of lowish mode, i.e., no modes. I checked the battery voltage, and it’s at 4.13V, so wonder if either (a) the protection circuit is bad or (b) the whole battery is bad.
Would it be worth removing the wrapper and protection circuit and seeing if this battery would work ok as an unprotected?
I’d assume it was the protection circuit.
ANNNND, with that, you’d be correct :)!!
I removed the protection circuit, and re-wrapped the battery, and now I get modes when I use that battery :)!!
Re. 3) I’ve tried several different 14500s (paired with a dummy… NO COMMENTS PLEASE :)!!), i.e., with 1x14500, and I get consistent 1.43 - 1.44 amps at the tailcap.
I have been trying to measure tailcap current with 2 x 14500, but not having much luck… I’m not sure why. The light/host I have this in has female threads at the tailcap end of the tube, so I’m having a hard time making contact with the threads because they’re inside the battery tube, I think.
EDIT: I don’t know what current the stock driver does with 1x14500.
I hated doing it, but FYI, I decided to sand off the ano on a (small) area of the end of the battery tube, so that I could just use a test cable with alligator clips with the meter. I then measured tail cap current with 2x14500 (Efest IMRs) and remember this is with 3 x XP-G2 emitters.
Anyway, tailcap was about 0.92 amps. I guess “theoretically” and not taking any loss into account, that should give about 2.45 amps at the emitters, or ~0.81 amps per XP-G2?
The measurement was a quick one, less than 5 secs, I guess. Should I run it longer on high to see if something smokes?
EDIT: My test cable is one of my “regular” ones, from Radioshack, about 18” with alligator clips at both ends. I was also just using my normal test leads on the meter, probably a meter each:
EDIT 2: My “theoretical” calculation:
Power in = 0.92 amps x ~8 volts = 7.36 watts
Total Emitter current = Power/Vemitter = 7.36 watts/3 volts = 2.45 amps
Per emitter current = 2.45 amps/3 = 0.816 amps
I don’t see why anything would smoke. I also don’t see why output is so pitiful if you’ve still got a stack with R200/R200/R100 on there. I’d expect efficiency to drop but output to go up. Something is limiting performance and I doubt that it’s the batteries. I don’t really know what is doing it. Possibly the TOFF cap needs to be adjusted for higher currents?
BTW what host is that?
EDIT:
I note that you did not include losses in the driver. As usual, I’d say 80% is a good number. So we’re actually looking at about 5.89W/3xEmitters = 1.96W per emitter. So maybe more like 2A output. Odd.
This is the host:
Also an RC-G2 W/quad…right now limited to 1 x 14500 or 2 x 14250, but waiting to get an extension made.
BTW re the current calculations, that’s why I wrote “theoretical” and put that in quotes :)…
EDIT: Corrected mispelling (my tablet keyboard’s auto-suggest :laughing:.
Just to eliminate possibilities, I re-tested the 2x14500, but with a pair of short (less than 12”) 20 AWG cables, and got exactly the same current at the tailcap, ~0.92 amps.
Kind of strange :(!!!
I’m starting to think that what you said about there being SOMETHING on this driver that is limiting the current may be right. It’s acting almost like a current regulator?