This is a universal charger of Lithium Ion batteries based on Atmega8 microcontroller. As you may know, LiIon batteries have many advantages comparing to regular NiMh or NiCd. Main of them are: high capacity by weigh and volume, no memory effect, fast charge and so on. But these batteries require special charging algorithm. You cant plug to some voltage and expect them to charge. It needs non constant voltage and current during charging cycle. Charging generally follows these steps:
- Current control at the Max Charge Current is used until the battery voltage reaches the voltage threshold (normally 4.1 or 4.2 volts per series cell). The battery is about 70% charged at this point;
- The voltage is now controlled very accurately (this is very important) at the threshold voltage while the current drops off naturally. Once the current reaches the lower cutoff ( about 100 mA per parallel cell typically), charging is stopped after a top-off time delay.
Lithium ion battery charger for robotics - [Link]