Triac output optoisolator for AC load switching
The FOD4118V is a 1-channel optoisolator from onsemi with a triac output, designed to drive AC loads such as solenoids, motors, and lamps from a low-voltage logic signal. Its 5000Vrms isolation rating and 800 V off-state voltage make it suitable for 240 VAC line switching with margin for transients. The built-in zero-crossing circuit triggers the triac only when the AC voltage crosses zero, minimising inrush current and conducted EMI.
Parametric deep-dive: dV/dt immunity and trigger current
Static dV/dt is rated at a minimum of 10kV/µs — this means the output triac will not falsely trigger on fast voltage transients from inductive load switching or mains-borne spikes. In a motor-drive application, that immunity saves the nuisance tripping that a lower-rated optoisolator would cause. Hold current (Ih) is 500 µA — the triac stays latched once triggered as long as the load current exceeds this value.