Patent ID: 8476853

Claim:
A power tool powered by an alternating current (AC) input signal, comprising: a motor switch coupled in series with an electric the motor; a motor control module interfaced with the motor switch and controls switching operation of the motor switch, wherein the motor control module is implemented by computer executable instructions executed by a computer processor; an overspeed detection module that is separate from the computer processor and operates independently from the computer processor to determine rotational speed of the motor and issues a disabling signal to the motor control module when the rotational speed of the motor exceeds a threshold, wherein the motor control module opens the motor switch in response to the disabling signal from the overspeed detection module, thereby discontinuing motor operation; and a protective switch connected across an AC line carrying the AC input signal and a fuse disposed in the AC line, where overspeed detection module closes the protective switch when the rotational speed of the motor exceeds the threshold, thereby shorting the AC line and opening the fuse.