Patent ID: 7205748

Claim:
A charging circuit for a secondary battery, comprising: a constant-voltage circuit part that selects and outputs one constant voltage among a plurality of predetermined constant-voltages in response to an input control signal and charges the secondary battery by applying the selected constant voltage thereto; a detection circuit part that detects a battery voltage of the secondary battery; and a control circuit part that controls the selection of a constant voltage applied from said constant-voltage circuit part in response to the detected battery voltage from said detection circuit part, said control circuit part causing said constant-voltage circuit part to charge the secondary battery by applying a predetermined first constant voltage thereto when the battery voltage of the secondary battery is equal to or less than the first constant voltage, and to charge the secondary battery by alternately applying thereto a predetermined second constant voltage and a predetermined third constant voltage that is lower than the second constant voltage in a constant cycle when the battery voltage of the secondary battery exceeds the first constant voltage; wherein the second constant voltage is higher than the first constant voltage.