I have a radio shack "AA" battery holder that holds 4 "AA" cells. I rigged it so it only holds 3 cells and the fourth battery slot holds a 3.3v LDO regulator, this is very nice, I have an off/on switch and regulated 3.3v output in a nice enclosure for cheap.
I want to cut a hole in the side of it so I can plug in a USB cable for charging. I would like to do this with discrete components that I already have on hand and not have to order anything if possible.
Does anyone know of a simple trickle charging circuit for 3 NiCad or NiMh cells. USB only puts out 5 volts so I don't have enough overhead to use a L317 variable regulator.
Later I would like to add more functionality like a smart charge controller, maybe a low battery light/cut off, excessive current light/cut off, and maybe make that usb port functional so I could monitor current and voltage in real time with an app on my PC, but for now I just want simple trickle charging functionality from 5 volts.
I want to cut a hole in the side of it so I can plug in a USB cable for charging. I would like to do this with discrete components that I already have on hand and not have to order anything if possible.
Does anyone know of a simple trickle charging circuit for 3 NiCad or NiMh cells. USB only puts out 5 volts so I don't have enough overhead to use a L317 variable regulator.
Later I would like to add more functionality like a smart charge controller, maybe a low battery light/cut off, excessive current light/cut off, and maybe make that usb port functional so I could monitor current and voltage in real time with an app on my PC, but for now I just want simple trickle charging functionality from 5 volts.