Battery Operated Device Power supply

[soubitos]

Its in Chinese but somehow google translate gives a clear view if you copy paste text

[paulca]

I said back in reply #27 you need to *BUCK*, not boost.   If you buck to the lowest voltage your design can tolerate, you'll save most of the power being dissipated in those resistors or constant current LED drivers.

This is why for my solar setup I charge 12V battery packs and buck to 5V for USB device charging. 

(which as an aside all of the testing in this post has been solar powered).

The problem here is the margins involved.  The circuit seem capable of running down to about 2.9V when the MCU browns out and eventually crashes.

Bucking the 4.2V to 2.7V range of the 18650 limits me to the 4.2 to 3.x voltage range.  The x dependant on the minimum input of the buck converter.

I may misunderstand correctly but a buck converter only operates well when the input is above the output.

Thus I would need to buck down to 3 volt. 

That's possible, would be intersting to see the difference, but ... I'd need to build the buck converter or find and use a cheap module.  I can see there being 3.3V modules available easily, but not 2.9/3.0V modules.

[soubitos]

I can send you a TP4056FlexAdv mate.... on the house... I am sure you will solve all your issues... it can be charged by solar directly, take USB 5V, wall adapters of any kind (imp 8-45V), will charge and protect your lithium and has an MT3608 as a booster ... i say, you pm your postal address, i will put one in the mail in a couple days max, you will receive it in a week or so and you will post here how you find it!

[paulca]

I'm willing to test this out.