Patent ID: 7421594

Claim:
A bus power device comprising: a connector that is connected to a port of a host apparatus compliant with a predetermined interface standard; a current/voltage detecting unit that detects a current/voltage supplied from the host apparatus to a bus power line via the port and the connector; a power assisting unit that assists a current to the bus power line based on a result of comparison between the current detected by the current/voltage detecting unit and a threshold current, and assists a voltage to the bus power line by an amount of shortfalls in the voltage based on a result of comparison between the voltage detected by the current/voltage detecting unit and a threshold voltage; a secondary battery used by the power assisting unit as a power source to assist the current/voltage; and a charge controller that normally charges, when a separate power source is not connected to the bus power line, the secondary battery with a first charge current, and rapidly charges, when the separate power source is connected to the bus power line, the secondary battery with a second charge current larger than the first charge current, wherein the port is a low-power port that outputs low power, and when the connector is connected to the low-power port, and when the separate power source is not connected to the bus power line, the secondary battery supplies power to each section via the bus power line as a main power source.