Patent ID: 6967469

Claim:
A battery charging method of charging a battery, comprising the steps of: charging a battery from a DC power supply which is subjected to current limit with a power-supply limiting current value and is subject to constant voltage control with a first voltage, by a charging current of said power-supply limiting current value through a constant-voltage control unit which has a differential comparator circuit and whose current limit value is variable, wherein said constant-voltage control unit performs current limit with a first current value larger than the power-supply limiting current value and constant voltage control with a second voltage lower than said first voltage; making differential comparison between a charging voltage of said battery and a reference voltage corresponding to the second voltage with said differential comparator circuit; generating a differential comparison output, which is different from a constant-voltage control signal, from said differential comparator circuit when said charging voltage rises from a level lower than said reference voltage and said differential comparator circuit becomes a state of effecting linear operation; and changing said current limit value from said first current value to a second current value smaller than said power-supply limiting current value in response to said differential comparison output.