Power supply system for portable electronic devices

DETAILED DESCRIPTION Accordingly, it is an object of the present invention to provide a novel power supply system for a portable electronic device having a rechargeable battery, which adjusts the battery charging current depending upon the current consumed by the portable device.
It is another object of the invention to provide a portable device power supply system having low power loss and high efficiency battery charging.
It is still another object of the invention to provide a portable device power supply system capable of charging a rechargeable battery faster and reducing the charging time of the battery without enlarging the size of an AC adapter.
These and other objects of the present invention can be achieved by a power supply system for a portable electronic device operable on an internal rechargeable battery, which comprises: an AC adapter for supplying a variable amount of input power including a variable amount of system power for operating the portable device and a variable amount of charging power for charging the battery, a battery charging circuit for supplying a variable amount of charging current flowing through the output terminal to the battery, an input current detecting circuit for detecting an input current supplied from the AC adapter and for generating a detection signal having a magnitude which varies depending upon the input current, and a charging current control circuit for controlling the amount of the charging current in response to the detection signal.
In an embodiment, the charging current control circuit controls the charging current so as to be constant when the amplitude of the detection signal is less than a predetermined threshold level, and so as to decrease the amount of the charging current depending upon the amplitude of the detection signal when the amplitude of the detection signal is not less than the predetermined threshold level.