Patent ID: 7821233

Claim:
A charging circuit which charges a battery based on a power supply voltage from an external power supply, the charging circuit comprising: a charging transistor which is provided on a charging path from the external power supply to the battery; a charging control circuit which adjusts an ON state of the charging transistor to control a charging current supplied to the battery; and a voltage adjusting circuit which is provided on an electric power supply path from the external power supply to a power supply terminal of the charging control circuit and generates a voltage drop, the voltage adjusting circuit, wherein the charging control circuit comprises: a clamp circuit which clamps a voltage at the power supply terminal of the charging control circuit below a predetermined clamp voltage; and a current adjusting circuit which adjusts the ON state of the charging transistor such that a voltage of the battery is brought close to a predetermined voltage value, and wherein the voltage adjusting circuit comprises: a protection transistor which is provided on the electric power supply path from the external power supply to the power supply terminal of the charging control circuit; and a resistor which is provided between a terminal connected to the external power supply of the protection transistor and a control terminal of the protection transistor, and the clamp circuit clamps a voltage at the control terminal of the protection transistor below a predetermined threshold voltage, and thereby the voltage at the power supply terminal of the charging control circuit is clamped below the clamp voltage.