Triac output optoisolator for line-voltage switching
The FOD4208SD is an onsemi optoisolator with a Triac output, rated for 5000 Vrms isolation and 800 V off-state blocking, making it suitable for switching 240 VAC or 480 VAC loads with transient margin. With a 60 µs turn-on time and no zero-crossing circuit, it fires at any point in the AC cycle, enabling phase-angle dimming, soft-start, or random-fire control in industrial and appliance applications. The single-channel device comes in a 6-SMD gull-wing package for surface-mount reflow assembly, with approvals from cUL, FIMKO, and UL.
Parametric deep-dive: drive current, dV/dt, and temperature
Static dV/dt is a minimum of 10 kV/µs, providing immunity against fast voltage transients common in motor-drive, relay-coil, and solenoid circuits that could otherwise false-trigger a standard triac driver. Hold current is 500 µA typical, and forward voltage is 1.28 V typical at 30 mA maximum DC forward current, defining the LED drive budget.