Is it possible to identify and remove a PWM controller from a circuit?

Flashlight Modding and DIY Parts
17

Ok, I have virtually no equipment or workspace here tbh (I should be able to find a few wires more than a couple of inches…) but I’ll give it a go.

What do I touch the negative lead of the DMM to whilst measuring the pins?

… Ok, this might sound a bit amateurish (which is fair enough because I am one), but I’ve run into a few simple problems. Firstly, my wires aren’t really long enough to get stuff out of the way, secondly, my solder won’t stick easily to any of my primary cells, and I actually only have about an inch of solder left atm so don’t want to waste it up in multiple attempts and leave none for reassembly. Thirdly I don’t currently have any spare emitters to test with, the only available one right now is the neutral XP-G2 that came with the light on a tiny board which offers effectively no heatsinking, and I don’t want to overheat the emitter doing a test.

I don’t want to give up having come this far, but am considering just extracting the emitter (fantastic tint) and replacing it with a standard XP-G from another light before gifting it to someone who won’t care about either PWM or tint but will like a small stainless steel light.

18

just to clarify/add onto wights post: make sure to keep the led cool, keep it mounted in the head of the flashlight, or on a separate heatsink.

as to where you should stick your probe for ground: I think any ground will work in this case, but don’t quote me on that. battery neg., driver ground ring, chip ground. Just go for what is easiest.

19

Keeping it short here, I’m on a mobile device :

  • You’re almost certainly going to need more solder than that.
  • musicmagic is right about GND, get it where you can. I usually do it at the driver board, that way both my hands and probes are in the same place.
  • you may just have an iron that is not high enough wattage. Don’t worry about it, use a rubber band instead.
  • rob long wires out of whatever: old computer cables, old power cords, old 9v DC adapters, etc
  • musicmagic is right about the emitter as well. Install it in the head and keep runtimes short or use a fan.

Also don’t give up now :wink:

20

But... isn't there some way to figure this out that doesn't involve tools, supplies, or effort? (sorry, couldn't resist, just kiddin' :))

21

Ok, I applied a bit more effort and some elastic bands and have got an answer!

Readings for the 6 pin component on the B+ side, clockwise from the top left, with the writing upright on the component itself, were:
1.42, 4.91, 1.42, 1.43, 0, 0

Readings for the unmarked 6 pin component on the other side, again clockwise from the top left, (with the inductor to it’s right) were:
0, 0, 0, 0, 4.92, 0

I really hope this can tell something useful now that I’ve actually got it to work.

22

Good work. (but) This was definitely in Medium?

23

Oh, sorry, this was in low mode. I found a spare LED but nothing mounted to a heatsink and no way of properly doing so so I just ran it in lowest mode. That still uses PWM but at both a lower freq and with a smaller % on cycle. Does the reading need to be in medium?

24

Nah, just not on High.

I’m a little confused at the moment about that chip on the inductor side. All those zeros…. Hopefully I’ll have a moment of clarity soon.

25

Would you mind sharing what you’re looking for? What would suggest a PWM related pin?

I’ll try retaking the readings as well instead I made a mistake first time, I did do it twice already though to confirm.

26

I believe that your measurements are not correct. You said that you measured the unmarked chip starting clockwise from top left (with the inductor on the right). Using your numbering shouldn’t the value for 5 and 6 be the same?? I see that they are sitting on the same trace in your pictures.

Also, please determine LED voltage while running in Low (the mode you took the other measurements in).

27

Multimeters do not always give consistent results for PWM I think, but generally you’ll see a voltage between VCC (Vbat in this case I think) and zero. So like 0.5v or 1.0v or something would potentially indicate PWM.

We aren’t just looking for PWM though. It’s much easier to do a quick test of all the voltages than guesstimate where all the traces go (under components and stuff), we want to know the location of GND and VCC on those chips as well.

I’m assuming that we are dealing with a dedicated boost controller which accepts PWM input, I could be wrong. Instead we could be dealing with something more hacky. Once you take another look at the unmarked chip we’ll come back to that.

28

Is that a FET on the non-inductor side? Can't he just bridge the 4.xx volts to its gate directly?

29

This is a boost driver… so no. If it’s not the output voltage then hooking it up to Gate will stop the boost circuit. If it is the output voltage then… well that’s even more Doctor Seuss.

30

I knew that. I was just testing you. You passed. I think.

Was hoping that if it was a bad idea (like it apparently is), it might trigger an idea on a different approach. Please resume your regular programming.

31

Ok, sorry. I had made two mistakes again due to rushing the readings first time, not a great day for me in terms of reliability… Firstly I don’t think I actually gave off ‘clockwise’ readings, but read it from top left then bottom left, below are genuine clockwise readings. Secondly, the unmarked component needed a bit more pressure on some of the legs to show readings, so I have a couple of extra non-zeros. Below are the ‘real’ results (assuming I haven’t made anymore mistakes).

Battery contact side

1.4, 1.4, 4.9, 0, 0, 1.4

Inductor side (inductor to right)

0.1, 0, 0, 0, 4.9, 4.9

Led voltage reads as 1.24v, which surely cannot be right for an XP-G. But my DMM does give reliable readings otherwise, maybe the PWM is throwing it off a bit.

Some more interesting readings from the inductor side component bridged to the LED negative output from the driver are shown below. I’m not sure if they’ll help, but they seemed interesting to me. The 0.1V deficit of the first pin compared to the next 3 matches the 0.1v reading it gives bridged to negative driver input, and the 1.25s match the readings from the LED, I don’t know what that means though.

2.6, 2.7, 2.7, 2.7, 1.25, 1.25

32

Frankly I have absolutely no idea what you are describing in your last paragraph. I’m chewing on the rest.

33

I’m really frustrated. It’s important to not mix stuff like that up. My model of how the driver worked and where invisible connections existed is just blown out of the water now.

If you get bored, please do the same readings on medium.

I’m definitely out of steam on this one for now.

If necessary maybe you can drop the LED into a glass of distilled water or something for cooling while you do the tests.

34

The last paragraph was measurements taken from the chip on the inductor side with the negative lead on the driver end of the wire connecting to the LED negative, I’m not sure if they were relevant though.

I’m sorry to mess you about with mistakes, and do appreciate your help. I’ve just got readings on medium, but having done a few tests three seperate times I got slightly different results on some pins.

So, clockwise for the chip on the battery positive side I got all three times:

0.8, 2.8, 0.8, 0.05, 0.05, 0.65

On the chip on the inductor side (clockwise starting left to right with inductor on right) I got on two of the three tests:

2.75, 0.05, 0.05, 0.05, 2.77, 2.77

On the one anomalous test I got these for the inductor side chip:

1.4, 0.05, 0.05, 0.05, 3.78, 3.78

I’m not sure why the 2nd test was different, it’s possible the light bumped up to high mode as I flipped the assmbly over, but I didn’t notice at the time.

It was certainly in medium the third set of tests though and they matched the first results so I would go with those.

Just to clarify for absolute certainty, by clockwise I mean: 1. top left, 2, top middle, 3. top right, 4. bottom right, 5. bottom middle, 6. bottom left

35

Are there any more thoughts from anyone?

wight, I don’t want to rush you as it’s your own time you’ve been spending trying to work this out for me (which is greatly appreciated). But could you let me know if the new results on medium are more useful than the last ones?

The 0.8v pins match your description of a voltage between that of the battery and 0, both of those were on the B+ side chip.

36

Haven’t looked or thought about it since I stopped last night. Started looking again just now, but I’m still confused. Let’s just take a look at one chip, the one on the battery contact side.

Low: 1.4, 1.4, 4.9, 0, 0, 1.4
Med: 0.8, 2.8, 0.8, 0.05, 0.05, 0.65

Is that right? Pay close attention to the second and third pins. Third especially. From ~5v to <1v eh?

I think/worry/suspect that these pulsed signals have got your DMM so confused as to be less useful :-(.