A common and inexpensive integrated 555 timing circuit is used to vary the timing of triac firing pulses in response to a control voltage. A trigger pulse generator generates a pulse at each zero cross-over of an AC line. This pulse initiates a variable, one shot pulse generator which generates a rectangular...http://www.google.fr/patents/US5592073?utm_source=gb-gplus-shareBrevet US5592073 - Triac control circuit
