Patent ID: 7701178

Claim:
A circuit for controlling charging, which is configured to be coupled to a charger for performing charging with a constant current, comprising: a transistor provided on a charging path between a position of a charging terminal for receiving the constant current from the charger and a position of a battery; an input voltage detecting circuit configured to detect a potential of a point between the charging terminal and the transistor on the charging path; and a drive circuit configured to control an ON resistance of said transistor continuously between a fully conductive state and a fully nonconductive state in response to the potential detected by said input voltage detecting circuit between the charging terminal and the transistor so as to set the ON resistance of the transistor to any desired value between the fully conductive state and the fully nonconductive state, wherein the drive circuit controls the ON resistance of the transistor continuously to stabilize an input voltage of the charging terminal to a predetermined voltage.