Patent ID: 8217610

Claim:
A power tool comprising: a motor; a power source cord connected to the motor and having a plug constructed to be electrically connected to an electrical outlet; a phase control device constructed to perform a phase control of an AC power that is supplied to the motor via the power source cord, so that a rotational speed of the motor can be controlled; a power supply device constructed to supply a power to the phase control device for the operation of the phase control device; and a power source determining device constructed to determine if a power source supplied from the electrical outlet is an AC power source or a DC power source; wherein: when the power source determining device determines the power source to be a DC power source, the power source determining device outputs an OFF signal to the power supply device, so that no power is supplied from the power supply device to the phase control device; and when the power source determining device determines the power source to be an AC power source, the power source determining device outputs an ON signal to the power supply device, so that the power is supplied from the power supply device to the phase control device; the power source determining device is further configured to determine if the plug is connected to the electrical outlet; and the determination as to whether the power source supplied from the electrical outlet is an AC power source or a DC power source is made when the connection of the plug to the electrical outlet is determined.