The RasPi requires a steady 5V and to this end I build a power regulator circuit using a LM2576T, similar to the one on page nine of the latest MagPi magazine.
This works great with an external battery pack but does not provide a way to charge the batteries directly. I have to charge the batteries first before using them with my Pi. Ideally I'd like a circuit that can run the RasPi from the mains power adapter while charging the batteries and run off battery when disconnected from the mains.
I have 4x 3.7V 4200mAh 18650 Ultracells batteries and a battery holder with PCM
These batteries have a full charge voltage of 4.2V and cut off discharge of 2.75V
I've done a lot of Google searches looking for examples of both a power regulator and li-ion charger but so far not found what I'm looking for...
Is there a specific name for this type of circuit? Does anyone have experience building a circuit like this? Is there any reference documentation or example circuit diagrams you could point me to?