DUTY FACTOR PROBING OF A TRIAC-BASED DIMMER

摘要

A method of powering one or more lighting devices (LEDA, LEDB) from an output of a thyristor-switched dimmer circuit (8) comprises: converting power from the output of the thyristor-switched dimmer circuit (8) to supply the one or more lighting devices (LEDA, LEDB); predicting a next zero-cross time of a voltage of an AC power source (6) that supplies power to the thyristor-switched dimmer circuit (8); probing the output of the thyristor-switched dimmer by periodically or intermittently applying a minimum conductance across the output of the thyristor-switched dimmer during durations of probing cycles, wherein a rate of initiating the probing cycles is less than a half-cycle rate of an AC power source (6) that supplies the thyristor-switched dimmer circuit (8), whereby some half-cycles of the AC power source are not probed, wherein the durations of the probing cycles extend from a turn-on time of the thyristor-switched dimmer circuit (8)) at least until the zero-crossing predicting circuit has gathered sufficient information to predict the next zero-cross time of the voltage of the AC power source (6).