Besides of the mobile phones, the Lithium Ion batteries are becoming increasingly popular, especially in the robotic field. In the past, the robots are normally worked with Nickel-cadmium batteries, but it’s not as convenient as the Lithium Ion batteries did!

There are many advantages of using Lithium Ion batteries than other batteries, including:

1. It has high capacity by weight or by volume (It’s about twice of NiCads capacity).
2. The Battery packs are smart (We’re able to control charger settings according to our need).
3. No memory effect is required.
4. Lower self discharge, where less than half of NiCads is.
5. Fast charging speed (You only need about two hours to charge the Lithium Ion batteries that running out of energy to fully charged).

For building this universal Lithium ion battery charger, an ATmega8 should be used as the main circuit. In addition, a DC supply is needed, as it capable of providing at least 2 volts more than the max cell voltage.

The current and voltage control is managed by a PWM output into a P-channel MOSFET. Furthermore, a large inductor/capacitor combination would be perfect, as it used to stabilize the circuit.