Zero crossing detection of line voltage/current of variable amplitude

摘要

A method and apparatus for detecting a zero crossing or desired phase angle of a power line signal having a variable amplitude uses a ratio between a peak amplitude of the power line signal and the amplitude of the power line signal at a desired phase angle for a known amplitude version of the power line signal to detect when a variable amplitude version of the power line signal is at the desired phase angle or zero crossing. The detection of the phase angle is used to determine if a notch is present in the power line signal. A substantially constant width pulse is generated if a notch is detected regardless of the amplitude of the power line voltage or current. The invention is particularly useful in a lighting system for generating and detecting pulses used to communicate information from a power line communication controller to a series of electronic ballasts over a power line used to power the ballasts. The information can be used to control a dimming function of the ballasts.