Triac-output optoisolator for AC load switching
The MOC3021SM from onsemi is a 1-channel optoisolator with a triac output rated for 400 V off-state voltage and 4170 Vrms isolation between input and output. It has no zero-crossing circuit, so the triac can be triggered at any point in the AC cycle — useful for phase-control applications like dimmers, motor speed controllers, and soft-start circuits. The LED forward voltage is 1.15 V typical, and the maximum LED trigger current (Ift) is 15 mA. This means a standard 5 V logic output can drive it through a series resistor; the hold current is 100 µA typical, so the triac stays latched once triggered until the load current drops below that threshold.
Housed in a 6-SMD gull wing package, the MOC3021SM is suited for surface-mount assembly on mixed-signal boards where the optoisolator bridges the low-voltage control side and the high-voltage AC load side. The package is supplied in tube, not tape and reel.
Active lifecycle and sourcing position
The base product number is MOC302; the 'SM' suffix denotes the surface-mount gull wing package. If your board uses the through-hole version (MOC3021), the pin functions are the same, but the footprint differs — the SM variant requires a 6-SMD land pattern.