Patent ID: 7196911

Claim:
A DC power source unit selectively used for a power source of a tool and for charging a battery pack to be attached to the tool for an alternative power source thereof, the DC power source unit comprising: a switching power source circuit that generates a DC output voltage, the output voltage being capable of being set to any level selected from a plurality of levels; a first detecting circuit that detects the output voltage of the switching power source circuit; a switch connected between the switching power source circuit and the battery pack for selectively applying the output voltage of the switching power source circuit to the battery pack or the tool by way of an adapter; a second detecting circuit that detects a battery voltage; and a control unit that controls the level of the output voltage of the switching power source circuit in response to detected signals from the first detecting circuit and the second detecting circuit; wherein the control unit comprises: first judging means for judging whether the adapter is connected to the DC power source unit or not; first selecting means for setting an output voltage of the switching power source circuit at a first level when the adapter is connected to the DC power source unit; second judging means for judging whether the battery pack is connected or not; and second selecting means for setting the output voltage of the switching power source circuit to a second level which is lower than the first level and for charging the battery pack by applying the output voltage set to the second level.