DUTY FACTOR PROBING OF A TRIAC-BASED DIMMER

摘要

A power supply circuit for operating high-efficiency lighting devices from a thyristor- controlled dimmer determines the dimming value, i.e., the duty factor of the output of the dimmer by periodically probing the output of the dimmer. A minimum conductance is applied across the output of the dimmer during probing intervals that begin at the turn-on time of the dimmer and last until enough information has been gathered to correctly predict a next zero crossing of the AC line voltage that supplies the input of the dimmer. The dimming value is determined from the time interval between the predicted zero-crossing and a next turn-on time of the dimmer. The probing can be performed at intervals of an odd number of half-cycles of the AC line frequency so that a DC offset is not introduced within internal timing circuits of the dimmer. The AC line frequency can also be determined from a time interval between the predicted zero crossings.