DQG 26650 driver hacking

I had the negative probe clipped to the ground ring for everything in the most recent measurements.

I think I misunderstood something you said earlier:

Were you saying that the voltage on the run pin changes as modes change or that the LED+ voltage changes as modes change?

EDIT: Specifically what I’m asking is whether the voltage on the run pin changes as modes change. If so what kind of values are we seeing?

The 'run' pin at the LTC1871 has 0v with power connected but the light off, and battery voltage in all modes when the light is on. The battery voltage drops a little for each higher mode, but it's still the same as whatever Vin is.

What about this? (L/M/H/T - LTC1871 pins 6-10)

10 sense: 29kHz/890kHz/1.3MHz/1.3MHz
9 Vin: 1.45kHz/32kHz/656kHz/3.24MHz
8 INTVcc: n/a
7 gate: 45kHz/340kHz/657kHz/657kHz
6 gnd: n/a

Thanks, I had a serious misunderstanding about that. My theory in post #21 is now shown to be totally out of left field, clearly the Run pins voltage either enables the IC or puts it into Shutdown mode - that’s it.

  • It took a while to sink in but the LTC1871 is not an LED controller. It does not have dimming. It can be configured in several ways, including as a current-controlled boost regulator - this is how I suspect it is configured here. Dimming is achieved through some other means.
  • It seems that your list in post #23 must be wrong though? If the Run pin reads the same as BAT+ in Low/Medium/High/Turbo then surely MCU pin #3 must as well (since they are directly connected)?
  • I’m unable to identify the 8-pin semiconductor on the bottom marked 9426 / (i) AE Δ / L45C. I think that’s the Siliconix logo, but I do not know specifically what the part is. I assume it’s a FET of some type. Does anyone know?

Aarg, yes, just checked that again and you're right. So low is none of the output pins on, mid is #7, high is #6, & turbo is #5.

Dunno, but its source pins are in parallel with the AO4468, and its drain pins go to GND (AO4468's do not). Their gate pins aren't connected.

This chip does not have a fixed freq. I would say that those freqs are changing in response to some other factor. While the LTC1871 does not have dimming, I currently have no idea whether or how the LTC1871 is being used to reduce the output current for lower modes.

Let’s do some more voltages on the LTC1871. (boring, I know) I’d probably just do two modes, we just need to see what’s changing and what’s not.

Ith (Pin 2) - I’m totally having trouble understanding this pin. The second paragraph on page 8 of the datasheet is throwing me for a loop.
FB (Pin 3) should be 1.230v all the time [this one should just be a sanity check :wink: ]
Freq (Pin 4) nominal is 0.6v, but taking this closer to ground changes the frequency…
Pin 5 - is this connected to Pin 6 (GND), Pin 8 (INTVcc) or something else?
Pin 10 - is this connected to one of the FETs?

I know there’s only so much you can do, but better lit pictures would be great. Very diffuse lighting to cut down on the shadows.

Thanks. What you mean by the last line is that “Their gate pins aren’t connected in parallel / together”, right?

All 3 of those pins clearly connect to the “Base” pin of corresponding transistors, according to your markings in that colored-in picture you did. What happens after that is less clear. Maybe tracking things down that way would be easier than guessing based on voltages at the LTC1871.

Please tell me that it’s not just a pile of transistors messing around with the sense resistors. I’m not sure that’s possible, but all that stuff is suspiciously close together…

1 RUN B+ in all modes
2 Ith 1.52mV/226mV/380mV/.754V
3 FB 1.247V/1.234V/1.250V/1.289V
4 FREQ .623V/.627V/.639V/.680V
5 M/S 5.17V/5.19V/5.21V/5.26V

AO4468 gate:
24mV/.739V/1.791V/2.375V
58khz/696k/657k/657k

9426 gate: B+/0Hz in all modes

Correct.

edit: Resized/aligned images and turned it into a mouseover:

So what you're wondering is, is it just using a different resistor for each mode? Wouldn't that be a terribly weird way of doing it? Although I guess that would explain why there's also no detectable PWM at the LED+/-...

That's exactly what it does.

Shorting across the 2R0 makes medium brighter. Shorting the R500 makes high brighter. And (no bonus points for guessing this one!) shorting the R120 makes turbo brighter. Dunno where the low mode is coming from, since none of the MCU pins are active for the low mode it must be the default current supplied by... something else.

And a mirrored x-ray of the battery side, so the vias line up with the topside pic (most of them, anyway - what's going on under the LTC1871 is still a mystery).

Uhm, well then. I guess we know how to control this thing then. Does jumpering the turbo resistor affect the other 3 modes?

Do the 3 transistors which control this action get hot at all? I just can’t see the circuit well enough to see if these sense resistors are the inline kind (I think current can be sensed without putting a resistor inline with the load in some circumstances, but I’m not certain. If these are in line with the load, seems like they’d get hot.)

Here is the STAR firmware modified to run this light.
~~http://photo.jesusthepirate.com/blf/DQG-26650-TRIPLE/SRK_no_ramp_1.0\_\_DQG-26650_v002.c~~
EDIT: switch pin not set as input.

I added the 3 flashes on stepdown code from the clicky firmware.

If it works as is I’ll be a little surprised.

http://photo.jesusthepirate.com/blf/DQG-26650-TRIPLE/SRK_no_ramp_1.0\_\_DQG-26650_v005.c

  • Fixed SWITCH_PIN setup.
  • Fixed MODEx_PIN issues.
  • Moved function declaration to remove warnings.

I haven't noticed them making heat, but I haven't specifically checked them for that, either. The only part I noticed trying to burn my fingers was the big diode down at LED+. These are just limiting resistors. I could swap the resistor locations around, and change the mode order.

This must be the section handling the low mode, since the other 3 are already known:

The little 180 (or 18C?) is the limiter, or the 010? What's a '010' anyway? My go-to decoder page says it's not a valid marking. Through that 010, there's a direct path to the #3/FB pin at all times. I haven't tried, but I'd assume that shorting the 010 resistor there would affect all modes, unlike the other 3 resistors that all work independently (in mid, shorting the H or T resistor has no effect; in high, shorting M or T has no effect, etc.).

Resistors like R120 and R500 are definitely sense resistors, not limiting resistors.

You may be able to directly measure the resistance of those two resistors you’ve got in the red box. What does that show? I’d measure both directions on each. I’m not sure how the transistor (or whatever) & capacitor there affect the operation of that section.

Basically the whole board could be “low mode stuff” since low mode is just a baseline and all the other modes are higher. Almost any of the small components could be involved with setting the baseline current and voltage… But yeah, that section is a suspect.

Your latest pictures show that there should be a break in the green line in your colored-in pic. Each of the sense resistors connects (through a dedicated transistor) to the big copper pour on the back which attaches to the FETs.

Due to the camera orientation, I cannot see where the via between the big cap and the red box you drew connects.

Immediately to the left of your red box there is a via, this appears to head down to the diode marked XL, through a resistor, and then on to Vin (Pin 9). I don’t think that’s what’s really happening, that’s just what I see.

Personally I am much less interested in this driver board now that I realize that it does not use a dedicated LED controller. It is very complicated for what it achieves.

FWIW, the FB pin is for setting voltage, SENSE pin is for setting current. I think.

Is there a path between LED- and the big copper pour on the back of the board when:

  • the light is off
  • the light is in low mode?

obviously there’s a path for M/H/T