Hi!
TL;DR: What is the jellybean li-ion solar charger IC?
I have this idea in the back of my head to build a nice little solar power bank. Nothing fancy, just 1W cell (possibly 2W if I feel generous). Something like the stuff chinese sell you, but actually working. I really like the idea of putting the cell onto my bag (on the lid, for example), and let it work for a day or two. This could be really useful for long trips, where I won't see electrical outlet for a month or more, and don't want to carry a lot of batteries.
I ordered some thin film solar cells from ebay, and will test if they are any good (is there any better source with reasonable pricing?). But now my question is how to get the pixies from the cell to the battery :-).
I searched online for some time, but most of the stuff is for large installations and buck topology. I have found the BQ25504, which is kind of what I want, but it's QFN only, rather limited current, and pretty expensive (which makes mistakes in soldering QFN even more expensive).
I even bought a cheap chinese charger/bank, to see how they do it, and perhaps buy a chinese IC from aliexpress and such. Well, they don't. The panel is connected via SS14 diode (if I can trust the markings) directly to the battery. I wonder if it's enough, given there are enough cells in the panel, and the maximum power point is approximately in the range of battery + diode drop voltage.
I'm already thinking how to do this on my own. Some micro, a boost converter (I really like the MCP16251/2, but the current capabilities have little reserve), and PWM the output from boost converter (set to target voltage, 4.2V) via a mosfet and proper filtering. I could implement a crude MPPT like this, and with some tuning it could start gathering electricity even under very little light. Depending on the solar cell voltage, I could even insert a bypass mosfet (some MCP boost converters already have it) and turn off the switcher if the voltage on cell is higher than the battery AND the battery is not fully charged (but I'd rather not to, as there is the need for extra ragulator, for the end of the charging curve).
But before I do that (I can't really devote much time to it right now), I wanted to ask here.
Is there any IC/technique I'm missing, that would make my life easier? How is it done in the commercial world? What are your suggestions?
Thanks!
PS: I have used the search field in here, and found one post similar to mine, but with no results at all. Everything else seems to be related to high-power stuff (or possibly scammy kickstarter).