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

My SK98's cut-off voltage is definitively set too low at 2.625V, after a second test it completely blacked out in low mode. The onboard XC6221 voltage regulator's minimum drop is 80mV, this means the PIC12F683 is Vin sensitive. This is all guesswork and I just share this here in case someone can confirm these microcontrollers are expected to be so low input voltage picky.

The above black out was caused by a failing switch.

Cheers ^:)

Tue, 10/02/2018 - 01:21

My SK98 started misbehaving, random flickering and it ended up turning off. I took the time to dismantle the whole driver thing to check contacts, some caps I had replaced were refitted and replaced again, redid wrecked spring bypass, increased driving current a bit, etc. Started working again but soon failed once more, random flickering and strange behaviours like low battery warnings and other moon output periodic flickerings. Refitted the low voltage warning divider which was giving me strange readings on my modified R11, reverted it to stock (R11 = R12 = 100KΩ). Still no dice. I wonder what could went wrong, maybe capacitor C15 broke? C15 is in parallel with R12, at the low input voltage divider. Hope someone can help if not what a pity.

Cheers ^:)

Switches. Switches crapping out, and I had unnecessarily messed with the whole driver.

After replacing the tail switch once more, took the stuff for a walk. Started giving me early current tapering and low voltage warnings, previously noticed with multimeter in amperimeter mode tailcap readings for the sake of it. Today I checked the R11/R12 divider, the R11 value leaned to ≈40K for some reason, for a cut-off at 3.75V or slightly above (cells were reading ≈3.8V pulled out from the flashlight after low voltage warnings). This means the divider works inversely as I had thought. If someone could confirm this I'd be grateful, so much tail switch crapping out got me nuts. :facepalm:

Next is managing to make a MOSFET tail switch for this build.

Cheers ^:)

this will reduce output of max mode only or all modes proportionally?

mobydimk, swapping the sense resistor value changes all modes proportionally.

Cheers :-)

After a lot of driver messing I recognized an unseen tiny debris short-circuit between C15's body and terminals, the capacitor next and in parallel to R12. That was the cause for the random/instant low voltage warnings. :facepalm:

R11/R12 divider works as it was supposed, thus R11<R12 for lower than 3V cut-off.

My SK98 works. Thank God.

Cheers :-)

:+1:

Glad you got it sorted out Barkuti. :wink:

Any idea when the BLF Boost driver will be available on OSHPark for DIY?

What are you calling the “BLF Boost driver”?

The one that Schoki was working on, I believe it is the same one that MTN Electronics is selling. My understanding is that it was supposed to be available to get DIY boards from OSHPark at some point, and since MTN is out of stock, and has been, it would be nice if we could get the boards to work on if we are comfortable with doing that.

There were 2 drivers developed on BLF, one by Schoki and the other by Lone Oceans. Neither was finished.
MTN Boost is a separate development.

i believe the Lone Ocean’s driver is finished, just need some more testing( which happens i can help him :stuck_out_tongue: ) and some firmware touching

I belive Schoki will have one in the near future

Finally some MT-G2 6V Love

Sketched out the schematics of the BW-ET1, for those interested.
I hope it’s readable.

So they built a buck-boost converter by daisy-chaining a TPS61021A (boosts to a fixed voltage, 3.3V I think) and a TPS62095 (steps back down to current set by op amp). A small dedicated 3.3V boost converter feeds the µC in AA operation.
The op amp operates more like a comparator that compares the voltage drop across the sense resistor against a filtered PWM output from the µC. No direct feedback, no fixed gain, the converter itself is the feedback loop. (I kind of understand how this works, but I’m no EE guy).

The CC control scheme looks solid but Blitzwolf messed it up with bad PWM.

Efficiency isn’t going to suffer much from this arrangement I think since the buck converter achieves around 95% efficiency. The obvious downside is driver size (humongous).

I’m looking for information regarding the H1-A driver. Maybe someone can help me here.
I don’t know which revision i have. It should be fairly up to date as i bought this driver in november 2018.

a) Does the H1-A feature thermal shutdown?
b) What would be the maximum operating temperature for the H1-A?

Says it does, look on page 6 of the TPS61088 datasheet.

Thx!

hi mrheosuper, do you know where I can find the Lone Ocean driver and the Schoki driver? Is anyone selling them?