Buck and Boost Drivers, Testing, Modding, and Discussion (Pic Heavy)

I dont understand it but do know you are doing amazing things Jensen567. :+1:

For reference:


At first pass I think the GPIO pins of an ATTiny all line up pretty well. It seems plausible that power and ground could be dealt with although I admit I haven’t having studied the PCB. I think it’s worth a try. I’m willing to give it a go as soon as either 1) my next batch of H1-A drivers arrives or 2) I run out of reflectors and emitters to explore on the test rig where my “extra” driver sits right now.

I’m still happy to program the PIC. More about that soon :slight_smile:

Have you seen this project?

Seems there is no current regulation. Just voltage boost.

That tindie board would be useful for embedding in something that just needs a voltage source, but as kiriba pointed out it has no current regulation.

Doing the same reverse engineering on the KX70 now. Found out why the output isn’t regulated, they skimped on an LDO voltage regulator and went with a 0 ohm jumper link instead. This means the power supply for the op-amp, as well as the PWM voltage going to the op-amp will drop with battery voltage. Funniest part is that the pads are there for the regulator, so add in a $0.40 part from mouser and it should be fully regulated again. Standard SOT23 footprint for the regulator.

Micro controller also seems to be a different model, doesn’t match the pinout of the PIC or ATTiny. Might be a custom chip as it is unmarked. Will post the schematic when I finish drawing it.

Look at this beauty I've found, Jensen567. Treats your pocket with plenty of care:

20MM 10W 3-12V With Switch Flashlight Driver Board T6/U2 XM-L2/U2 LED @ diybox

Here are the H1-A scope plots, as well as a more readable schematic. We can see mode spacing stock is approximately <1, 10, 33, 99.

I also have the KX70 Schematic, and a simple upgrade. Will grab scope plots for KX70 when I get a chance. Here is stock, followed by a simple mod that will keep it regulated, and best of all the PCB supports it!

If we look at pictures of the PCB we can see the 0-ohm jumper to the left of the inductor, cleaning the board up and we see pads for an SOT23 regulator. Also, anyone have any guesses to a compatible MCU?

Don’t mind the big hole in the IC… That’s why we don’t short the output. This driver is back together and working though!

Have anyone managed to connect a e-switch to a H1-A?

I want to remember reading in some thread that it had been done, might have been the H2-C driver though.

I do remember reading about someone getting an e-switch on H1-A or H2-C, they were just shorting power at the MCU for mode changes.

If we rewrite the firmware we have 2 free pins that could be used for e-switch.

That was me, on a H2 - I think I was grounding pin 1, which is probably a bad idea, looking at the diagrams above…

Nevertheless, it scrolls through the modes.

Easy e-switch to change modes:

  1. Raise boost IC's pin 1.
  2. Between the power input trace and the boost IC raised pin, place a normally closed momentary pushbutton.
  3. Finished! :-)

Ild like to here more about converting to eswitch

Did you mean MCU pin 1? A normally closed momentary switch on MCU pin 1 would do what you describe, and is IMO a good option for e-switch on H1-A.

Putting a switch between the TPS61088 Boost IC pin 1 I don’t think would work, as the MCU won’t know power to the converter cycled. It is also very difficult to lift a pin on QFN package parts.

I have noticed an error in the H1-A Schematic, the resistor on Boost IC pin 19 (Ilim) should be 100k not 10k. I also would suggest we go to a 2.5V LDO regulator on both KX70 and H1-A vs the 2.8V LDO H1-A uses.

This would allow us to maintain regulation right down to the 2.7V minimum input for the TPS61088 IC. A big improvement I think we can make with custom firmware is a lower voltage cutoff for the LVP.

:facepalm: LoL! Sort of that, yes. Undercooked reply. :-)

By the way, is there some sort of really tiny latching pushbutton switch? I believe a tail MOSFET switch could be made using 2 × CR1216 cells, but heck…



I have a Lumintop Elfin which uses a tail MOSFET switch with a super tiny button cell. SR416 I think.

Working on the drawings for H2-C and I think I finally figured out the Boost IC, I believe it to be a Monolithic Power Systems MP3428.

I realized I was wrong about it being integrated switch, the MOSFET on board is just to between the boosted output and the LED+ terminal, not entirely sure of its purpose, but I will read through the data sheet.

They also feed the ground through 2 n-channel MOSFETs which are always on. Not sure why they did that either. Between these 3 drivers I have had quite a few “why did they do it like that?” moments.

What happens if we put a switch to control the grounding MOSFET gates?