A new charger system approach: The current and voltage control loops

This paper presents a lithium-ion battery recharging circuit with an improved charger system topology for portable devices and handheld gadgets. The proposed charger topology uses an operational amplifier with NMOS input for a smooth transition between current control loop and voltage control loop and to control a power pass element device. Using the above-mentioned abilities, a complete charging process, consisting of three sub-processes; automatically trickle charge, constant current and constant voltage mode are implemented. In the proposed new charger system topology, the charging behaviors of the Li-ion battery can achieve a better charging performance and terminated automatically when fully charged. Simulation results show that the power pass element channel width is 40,000 µm which is less 60% from others design, is able to carry out the output voltage of 4.2 V, the maximum charging current reaches 1 A and the trickle charge is 10% of constant current. The new charger topology has been implemented using 0.18µm CMOS process. Experimental result shows that the new charger design topology agrees with the charging behaviors from simulation results.