Patent ID: 7446493
Filing Date: 2008-11-04
Classification: H02K,H02M,H02P

Abstract:
1. A motor control module configurable to control a given tool motor of a corded AC power tool powered by an AC supply voltage signal input thereto, the module comprising: a triac for controlling current to the given tool motor, and a controller for controlling a firing angle of the triac to control the amount of current applied to the tool motor, the controller having at least one digital input and including a digital blanking circuit for detecting voltage zero-cross signals in a given AC half-cycle of the AC supply voltage signal, wherein the digital input digitizes the input AC supply voltage signal into a digital signal, and wherein the digital blanking circuit detects valid zero-crosses in the digital signal by accepting a first zero cross transition of the AC supply, as represented in the digital signal, as a first valid zero cross signal in the given AC half cycle, rejecting additional zero crossings in the digital signal for a given blanking period, and then accepting a zero cross occurring at a next opposite polarity transition after the blanking period has elapsed as a next valid zero cross signal in the given AC half cycle.