Patent ID: 7365515

Claim:
A universal battery charger for charging batteries with different number of cells connected in series, comprising: a power supply circuit that produces a DC output voltage, the power supply circuit including a first switch circuit to control a level of the DC output voltage; a second switch that is connected between the power supply circuit and the battery and is turned ON to allow charging of the battery and OFF to interrupt the power supply circuit from the battery; an output voltage detecting circuit that detects a voltage level of the DC output voltage of the power supply circuit; a battery voltage detecting circuit that detects a voltage level across the battery; an output voltage setting circuit that produces a predetermined number of voltages different in level; a control unit that receives a detected signal from the battery voltage detecting circuit and sends a control signal to the output voltage setting circuit to select one of the predetermined number of voltages as a reference voltage; and an output voltage control circuit that compares the reference voltage with the voltage level detected by the output voltage detecting circuit to produce an output signal corresponding to a difference between the reference voltage and the detected voltage level, the output signal of the output voltage control circuit being applied to the first switch to control the level of the DC output voltage of the power supply circuit; wherein the control unit includes means for controlling the second switch to turn ON and OFF, and means for producing the control signal applied to the output voltage setting circuit to select a voltage level which is close to the detected voltage level across the battery when the second switch is turned OFF and the control unit detects that the battery is connected to the battery charger.