Simple SSR has zero-cross on/off switching

This Design Idea is a solid state relay (SSR) which uses a triac to switch AC loads at high current. There are plenty of simple SSR circuits available, but this may be the simplest circuit that achieves turn-on and turn-off only when the AC line voltage is near zero. Figure 1   AC SSR schematic with zero-cross switching (use browser zoom or open in another tab to enlarge) Transistor Q2 acts as a clamp to di ...

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