Triac Output Optoisolator for AC Load Switching
The FOD420SV from onsemi is a single-channel optoisolator with a Triac output, designed to switch AC loads from a low-voltage logic input. It provides 5000Vrms isolation between input and output, making it suitable for mains-connected applications like solid-state relays, motor starters, and industrial PLC outputs. With a 600V off-state blocking voltage and a minimum static dV/dt of 10kV/µs, this part resists false triggering in noisy environments such as inverter drives and switching power supplies.
Key Ratings for BOM Fit and Drive Margin
The LED trigger current (Ift) is 2mA maximum, allowing direct drive from a 3.3V or 5V GPIO without an external transistor — a BOM simplification for digital output modules. Forward voltage is 1.28V typical at rated forward current. This part has no zero-crossing circuit, meaning the Triac fires at any phase of the AC waveform. That enables phase-angle control for dimming or soft-start but also generates higher conducted EMI — account for filtering in the layout. Operating temperature spans -55°C to 100°C, covering industrial and outdoor telecom enclosures. The hold current (Ih) is 500µA typical, which sets the minimum load current to keep the Triac latched once triggered.
Package and Compliance Checklist
Packaged in a 6-SMD gull-wing with supplier device package 6-SMD. The gull-wing leads provide visual solder-joint inspection and are compatible with standard reflow profiles. Approvals include cUL, FIMKO, UL, and VDE — covering North American and European safety certifications.