US Patent 7861796 Method of operating drill with solid state speed control

A method of operating a hand power tool in one embodiment includes generating a variable speed control signal with a solid state switch that corresponds to a selected speed for a motor, generating a pulse width modulated (PWM) signal corresponding to the variable speed control signal, generating H-bridge driving signals for an H-bridge circuit in correspondence with the PWM signal, and selectively coupling a motor to a power source using the H-bridge circuit in accordance with the H-bridge driving signals.