Switching circuit for triac with AND=gate - is used for synchronising switching commands with AC load currents passage through zero

摘要

The turn-on circuit, for a triac, has an AND-gate (6) receiving switching commands at one input and connected at the other to a threshold circuit (5) that detects the passage through zero of the ac current being switched by the triac. This threshold circuit in fact generates turn-on synchronising pulses. The AND-gate drives a pulse generator (8) via a timer circuit (7). The pulse generator is coupled by a transformer to the triac's gate. The timing circuit produces a 1 ms pulse that triggers the pulse generator.