I am working on a project that has a micro-controller that needs to keep track of time over long periods, the project will be powered of mains power for the vast majority of the operation time, but I wanted to incorporate a backup battery for blackouts, or I'm clumsy and knock the plug out or something.
I have a few tiny li-po batteries that I have unused from a past project and wanted to try and reuse one. I also wanted to try and keep the circuitry simple without needing exotic ICs. As far as the charge cycle for li-po batteries is to charge at a constant voltage, with the current being limited to a certain value, this usually being done through a special purpose IC.
I wanted to know if it would hurt an Li-po or pose any safety hazards if I was to charge the battery just using a voltage regulator and a largish resistor to limit the current to a few milliamps.
I am pretty new to circuit design and this is what I thought would be a good starting point, I just wanted to be able to check here first because of the danger in li-po batteries being charged incorrectly.
(The resistors on the voltage regulator should set it to approx 4.2v)
Any comments and tips would be appreciated.
EDIT I should have mentioned that, when connected to the wall outlet it will draw a couple hundred milliamps, but I plan to have it sense when disconnected and go into a sleep mode only keeping track of the rtc, I don't have any numbers yet but I anticipate a current draw to be less than 10uA I did play around with the idea of using a large capacitor but unless I am doing my calculations wrong using a 10mF capacitor I would get a few hours at absolute best.