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I've had a cheap 18650 flashlight for some time now - when turning it off and on, it cycles through five modes - full power, medium power, low power, strobe, SOS signal.

I'd like to disable that feature and just use it in full power mode whenever I turn it on.

enter image description here enter image description here

I assume the "HL6S2" component controls those modes, but I couldn't find any useful information on that.

Positive power comes through the via near the red lead. Ground is on the perimeter of the chip. The flashlight is turned on and off via a switch on its back, which connects the case to the battery ground, so the IC seems to have some sort of memory to retain its information for prolonged periods of time.

I assume the IC switches the left leg (connected to the blue lead via two 500 Ohms resistors in parallel) to ground, which is on its middle leg. Does anyone have a datasheet for this chip? Searching for the markings wasn't very helpful.

To mod it, I'd remove the IC and solder a bridge from the left to the middle port - does that sound reasonable?

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    \$\begingroup\$ Option 1 spend 15 hours on wrong turns and dead ends trying to improve Alibaba cheapie, and ultimately fail. Option 2 work in a menial job for 2 hours, and use wages to buy high quality flashlight that does exactly what you want. \$\endgroup\$
    – Harper - Reinstate Monica
    Jul 5, 2020 at 17:35
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    \$\begingroup\$ @Harper-ReinstateMonica, we have all been at that fork in the road... \$\endgroup\$
    – P2000
    Jul 5, 2020 at 17:58
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    \$\begingroup\$ @Harper-ReinstateMonica That's boring. Might as well satisfy my curiosity, learn something new and perhaps help somebody else looking to mod those flashlights. \$\endgroup\$
    – towe
    Jul 5, 2020 at 18:36
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    \$\begingroup\$ Yeah, everybody thinks that. “Oh, I’ll learn stuff” and all you learn is sophisticated modern chips are more complex than you think they are, products made in million quantity have ASICs that are opaque, and banging your head into the wall hurts. Sink that same time into learning electronics in a structured curated course sort of thing, and you’ll be way way farther ahead. \$\endgroup\$
    – Harper - Reinstate Monica
    Jul 5, 2020 at 19:59
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    \$\begingroup\$ @Harper, I've already learned something I didn't know from Spehro's answer. This is not a repair question. It's a modification question. I learned much of my electronics from reverse engineering circuits many decades ago. I have voted to reopen. \$\endgroup\$
    – Transistor
    Jul 5, 2020 at 21:04

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The IC is an ASIC with built-in power transistor. You can do nothing with it, but bypass it.

Here is a similar part:

enter image description here

That one has 3 functions plus off (100%, 25% and flash), as clearly described in the datasheet. It also reverts into a low power mode to save the LEDs when the temperature is too high, and is protected against reverse battery.

Those resistors are 0.5 ohms, not 500 ohms, by the way.

Presumably if you can measure the forward voltage at 100% power you can replace the chip with a resistor. It's possible they've got an amazing n-channel FET in there with negligible Rds(on), as your 'just short it out' comment suggests, but I would not count on it.

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  • \$\begingroup\$ At 100%, I've got a forward voltage of 2.9 V and a current draw of around 1.4 A. With the ASIC bridged, it draws around 1.55 A of current. \$\endgroup\$
    – towe
    Jul 5, 2020 at 19:00
  • \$\begingroup\$ Your ammeter will drop a significant amount of voltage. It would be better to measure the voltage across the chip (pin 1 to 3) and across the resistors at 100% setting with no ammeter in the circuit. I can't tell for sure but it looks like the resistors are in parallel so 0.25 ohms? \$\endgroup\$
    – Spehro Pefhany
    Jul 5, 2020 at 19:03
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    \$\begingroup\$ I measured the voltage without the ammeter, then the current with the ammeter in place. Yes, the resistors are in parallel. Since the cooling seems to be relatively good, I decided to short the ASIC for now. I'll let it run for a while to see if it survives. \$\endgroup\$
    – towe
    Jul 5, 2020 at 19:11
  • \$\begingroup\$ You going to reveal those voltages? Just out of interest. \$\endgroup\$
    – Spehro Pefhany
    Jul 5, 2020 at 19:12
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    \$\begingroup\$ @lowe Sphero is looking for you to set the meter to low volt (e.g. 2 volt range) and put the 2 probes on Vdd and Vout. Also to put the probes on both sides of the resistor. Yes, really, with power on, max light, and on volt setting. The answer will be some number of millivolts. I know that it seems weird to want that measurement, but I think I see where Sphero is going. \$\endgroup\$
    – Harper - Reinstate Monica
    Jul 5, 2020 at 21:30
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Here’s the problem. You need to actually see the data sheet of that ASIC to see what else it does.

I polo mean, obviously, what annoys you is the multiple modes, and that’s what you want to change. But that target focus is making you and several others here to create a false narrative, that the annoying mode select is the only thing that chip does.

That is highly improbable.

After qaffgw. all, we’re dealing with a lights made in tens of millions quantity. T here are several other tasks that need to be done in a flashlight like this,and here are two:

  • battery protection for the LiPo
  • current limiting for the LED so it can be driven at peak performance.

That little 3-pin chip is in a good location to do both those things. Given that these chips are made in million quantity, it would be completely insane to not include those functions in that chip (thus forcing flashlight builders to use 2 chips).

You need to find this stuff out.

And the problem with niche ASICS like this is, there may not exist well-detailed documentation on these chips. Why would there need to be, everyone in Shenzhen who makes cheap flashlights knows each other... and all they need to know is”follow the schematic”.

To the extent they do document, it’ll be in Chinese, and they’re not going to do an English translation for something this niche.

I get where there’s ”fun trying”, but that is a very time-expensive way to learn electronics. You’re not learning much, and it’s bad lessons.

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Since you are on this site, curious and inquisitive, I assume you'd much rather modify the design, rather than work 2 hours in a menial job to buy a different flashlight.

So what you could do is use the push button to switch it on (100% was the first mode in the cycle?), and for switching OFF you could solder a second "normally closed" push button to cut off power from the battery. This would work if the flashlight powers up in OFF.

Should it power up in ON, then you'd have to use a normal toggle button in replacement of the current one.

But if it doesn't start with 100%, then you'd have to replace the whole control unit with a resistor to set the current, or use a regulated current source.

The resultant joy and satisfaction from making your own mod can never be supplanted by any amount of cleaning or burger flipping.

I also think this is the reason whay many of us are here, so you are in good company.

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