Electrically Isolated Zero- Crossing Detector

All power control circuits that use phase control require an adjustable delay element synchronised to the mains voltage. The adjustable delay determines the phase angle at which the thyristor, triac or transistor connects the mains voltage to the load. Simple passive dimmer circuits use RC phase shifters having a fixed relationship to the mains frequency. Nowadays, microprocessors are often used for precision controllers and complex control tasks.