Patent ID: 7061209

Claim:
A battery charger adapted to supply current to a removable battery pack comprising battery cells and a charging terminal, comprising: a first terminal for coupling to an external power source; a second terminal for coupling to the charging terminal of the battery pack; a power source circuit coupled to the first terminal and the second terminal, the power source circuit transforming voltage input from the external power source, and supplying charging current to the battery cells; a voltage detector detecting the voltage input from the external power source to the power source circuit; a processor coupled to the voltage detector and the power source circuit, the processor determining the amount of charging current supplied to the second terminal based at least upon the external power source voltage detected by the voltage detectors; a first temperature sensor coupled to the power source circuit, wherein the processor determines the charging current supplied to the second terminal based further upon power source circuit temperature sensed by the first temperature sensor; a second temperature sensor coupled to the battery cells, wherein the processor is coupled to the second temperature sensor, the processor determining the charging current supplied to the second terminal based further upon battery temperature sensed by the second temperature sensor; the processor (1) determines a first charging current value based upon the external power source voltage and the power source circuit temperature, (2) determines a second charging current value based upon the battery temperature sensed by the second temperature sensor, and (3) selects the smaller of the first and second charging current values as the charging current that will be supplied by the power source circuit to the battery cells; wherein the power source circuit includes a transformer which comprises a primary winding coupled to the first terminal, a first secondary winding coupled to the second terminal and a second secondary winding coupled to the voltage detector, and wherein the processor determines the external power source voltage based upon the voltage of the second secondary winding detected by the voltage detector.