Patent ID: 6765317
Filing Date: 2004-07-20
Classification: H02J

Abstract:
A power supply module for use between an AC/DC power supply unit and an electrical power tool driven by an electric motor and powered by a rechargeable battery pack having a normal operating voltage and a relatively higher fully-charged terminal voltage, the power supply module comprising:an input connectable to a power supply unit and an output connectable, in parallel, to a battery pack; and an operating circuit connected between the input and the output for delivering DC power from the power supply unit to the power tool in parallel with the battery pack supplying DC power to the power tool, said operating circuit providing a DC operating voltage at the output between a normal operating voltage and a fully-charged terminal voltage of the battery pack, and providing an output current limited to a predetermined magnitude, said operating circuit comprising: a current comparator for determining whether the output current is less than or is increasing toward exceeding the predetermined magnitude and providing a corresponding first control signal, and a switching device connected at the output for controlling, in response to the first control signal, the power delivered to the power tool as a direct DC current when the output current is below the predetermined magnitude and as a pulsating DC current when the output current is increasing toward exceeding the predetermined magnitude.