BLF A6 FET+7135 Light Troubleshooting and Mod thread

We expect too much from these 7135 chips. They are pretty impressive for what they do, very convenient and cheap.
High frequency PWM is not their thing though.

Most firmwares use a PWM frequency of around 7-9 kHz for Moon mode, BLF A6 included.
At 8 kHz, a PWM duty cycle of 1/255 gives us an ‘on’ pulse that is only about 0.5 microseconds long. But the 7135s need about 2 microseconds before they start to turn on and another 4 microseconds before they are stable. In those 6 microseconds the response is like an under-damped control system. We have a transient ‘on’ peak, then it cuts back and then finally stabilizes where it is supposed to be. What we see with the 8 kHz PWM Moon mode is just the transient peak at 2 us. The timing and amplitude of this peak probably depends on the exact sample of 7135, cell voltage, the emitter, wire/track lengths, etc.

The ones I measured were groups of 6 or 8 from standard 105C/D drivers. Some types may be better, some may be worse and individual samples of the same type probably vary as well.

The only way I see to get somewhat repeatable output from different sets of hardware is to slow the PWM. A lot. The smallest pulse width needs to be at least a few microseconds more than the 6 microseconds stabilization time. Lets say 2 microseconds more. So we start with a minimum pulse width of 8 microseconds. (Conservative design would select an order of magnitude larger, we do not have that luxury here.)

If we want to get this 2us margin at a PWM duty cycle of 1/255, it translates to a PWM frequency of 500 Hz (1/(8us * 255)).
Or, we can decide to not use a duty cycle lower than 4/255, then we can get away with a PWM frequency of around 2 kHz (4/(8us * 255)).
If we apply this rule to 8 kHz PWM we are stuck with a minimum duty cycle of 16/255.

Most people will, however, object to the lower PWM frequencies. We also do not get a very low Moon mode.
In the end proper current regulation is really the way to go, not PWM.

Example 7.2 kHz PWM, 32/255 duty cycle. Even at 32/255 about a third of the ‘on’ time is wasted/unstable:

Now, if we cut back to 4/255 duty cycle, all we are left with is part of the unstable transient peak:

Agreed. At the 2kHz speed you described, it looks like a strobe light to me. And proper regulation is nice to have.

Proper regulation may be difficult, since it requires more hardware and might use an extra pin. On BLF-A6 there is an unused pin… but probably no room for another component or two. I wonder if we could make it power the LED directly from the MCU. It’d probably require a resistor to adjust the current to the correct level, but otherwise I think it might be feasible if it’s only used for moon. Then there would be three power channels — moon, 7135, and FET.

The 7135 abuse method seems to work well enough most of the time, if people aren’t too picky about the exact output level. Like on the A6, it seems to range from 0.26 lm to 0.55 lm, possibly more. Pretty wide range, but they’re all reasonable for “moon mode” use.

Has anyone seen this before? It looks like the light settles into a mode, notice the flicker and then it is stable? Please disregard the auto exposure, can’t change that on the phone video recorder. I am going to send a note to Neal, I am afraid it will quit altogether. I have used Keeppower 35A and 30Q batteries, verified the switch is tight and cannot disassemble the head. :frowning:

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Matt

To me it appears to be a crook earth somewhere.

Very hard to do with a camera that cannot be set to manual exposure! And it happens so soon after mode change that the exposure does not get time to settle in.

Same thing happened with my defective head on mode 2, 3 and 4. Will flicker for abit then settle down. Didn't see this behaviour in my new replacement head. Most probably bad solder (as usual) on the 7135 chip. Ask banggood for a head replacement.

If we speak about flickering, I see my A6 flicker after I switch it to the highest mode (turbo), there is a single short flicker (reduced brightness) after about half a second, not every time but often.
I know there is a unwanted flicker after switching from turbo to moon, but this is the other direction. Is this the sign of a problem or normal behavior?

I also would like to know if you would advise me to remove the MCPCB, which seems to be a forced press-fit as shown in the first post - is there a good chance that I can improve the heat transfer?

So just an update on my A6 5A head replacement; I received it a few days ago & all is good! :bigsmile: Now all 4 of my A6’s are together again lol I’m lovin the 5A tint more and more.

Can I use two CR123a batteries rather than one 18650 safely?

I have some surefire 123s laying around, and my 18650 got lost in shipping and won’t be here for a month or so. But my BLF a6 showed up! I really want to play with it, so i was wondering if i can use two cr123a batteries without hurting the flashlight.

I don’t think so. Too much voltage.

Edit: If you’re that excited you could use one and somehow spacer it. But two in series will make 6 volts+

Ahhh shoot. Thanks for the quick reply.

There arent really any alternatives are there?

Edited above.

mmm… seems pretty complicated and a little bit above my head. Thanks anyway!

The waiting game is in full force. Quickly import / exporters!

If you want it quickly, & you are in the US, then order from Richard/RMM at Mountain Electronics

BLF Thread:

MTN Electronics: LEDs - Batteries - Lights - Chargers - Hosts - Drivers - Components - 1-Stop-US Source

Batteries | Mountain Electronics

http://www.mtnelectronics.com/index.php?route=product/category&amp;path=59

Richard/RMM has Great products, VERY GOOD prices, VERY FAST shipping, and GREAT support.

Best Regards,

George

Illumn.com is pretty awesome too. The focus there is more on name-brand lights, but both stores have batteries and great service.

And, no, don’t try to use two CR123A cells. It will fry the driver, which has an absolute maximum of 5.5V, and it might fry other components too.

The A-6 is an ideal light for candle mode operation so if there’s a diffuser that fits with the head removed could someone mention it so it can be listed in the op?

Hello, new to these forums, but I received my BLF-A6 from Banggood a couple days ago and the flashlight would not turn on. The batteries are good and I can turn the flashlight on by completing the circuit by linking the battery to the frame with the tailcap portion removed. Also the flashlight can sometime be activated by having the tail-cap sit on top of the threads. Any tips on how this can be fixed, or should I return the flashlight to Banggood or contact the manufacturer. Thanks.

Likely the switch retainer is loose and not properly engaging the switch pcb to the tail cap. Use some needle nose pliers to tighten it. Better yet, remove the brass ring and pcb and clean them and the tail threads first with alcohol and a paper towel as there are often metal shavings or other detritus that interferes with proper threading. Then relube them and reassemble.

Edit- BTW, welcome to the forum, we fix stuff or make it better.

See first post - “Some flashlight basics:” to locate the error (e.g. battery tube, tailcap switchboard, switch, retaining ring …).

Mine had a too short battery tube which couldn’t get contact with the “outer area” of the tailcap. Banggood sent me a new battery tube so i could remove the workaround.

Both the 20-24mm and the 20-25mm fit the A6:
https://www.fasttech.com/p/1347102
https://www.fasttech.com/p/1140010

I like using these wand-type diffusers when walking along side the road. It shines like a lantern, so it is very visible to oncoming traffic from hundreds of yards away.

P.S. I do not remove the head when adding the diffuser. Works just fine that way. Besides, with the BLF A6, I’m worried about decapitating the LED whenever I unscrew the head.