A Micro Power Management System and Maximum Output Power Control for Solar Energy Harvesting Applications

A micro power management system is presented for solar energy harvesting applications. An inductor-less solution is proposed which facilitates on-chip integration of the system. We target at applications working in different lighting enviromments ranging from strong sunlight to dim indoor lighting where the output voltage from the photovoltaic (PV) cells is low. A charge pump is used to step the PV voltage up to charge a battery or directly operate the circuit. The power management system behavior is theoretically analyzed and the control strategy is derived to transfer maximum power from the PV cells to the battery or the circuit. Circuit design and low power techniques for the maximum output power control are proposed for the system. The system was implemented using 0.35 mu m CMOS process. With the measured PV cells output characteristics, HSPICE simulations for the power management system were carried out to verify the control strategy and to demonstrate the system operation