Patent ID: 7605563

Claim:
A charging circuit for charging a battery, comprising: a generator operable to generate an output voltage; a step-down circuit operable to reduce the output voltage of said generator to a predetermined lower voltage; a current controller operable to control a charging current based on an amount of power generated by said generator, said charging current intended for supply from said step-down circuit to said battery, said current controller having a current-controlling element and a current-limiting resistor, in which said current-controlling element is a number of transistors; and a mode selector for selecting a charging mode from among a plurality of modes for charging said battery, said mode selector having a resistor and a switch coupled to the number of transistors of said current-controlling element so as to control a flow of base current therethrough, wherein said plurality of modes includes a current-preferred mode for maximizing the charging current supplied to said battery and an efficiency-preferred mode for maximizing utilization of the power taken out of said generator, wherein a total sum of a resistance component of said battery and a resistance of the current-limiting resistor is set to be not less than a negative resistance component of said current-controlling element.