Abstract
Some energy sources are left unused because they can only generate a small amount of energy. In order to utilize the small amount of electric energy generated from these energy sources, an electric power storage system is investigated. The storage system consists of a capacitor and a switching regulator. In order to obtain an analytic solution of the storage system, the system is approximated by an equivalent circuit, i.e., the energy source is assumed to have a linear I-V characteristic, and a linear approximation is introduced for the diode, the FET, and so on. The exact analytic solution for the circuit is obtained by normalized parameters. The optimum duty ratio is obtained as a function of the parameters such as stored voltage and power source voltage.