Triac-output optoisolator with zero-crossing detection
The onsemi MOC3043SR2M is a single-channel optoisolator with a triac output, designed to drive power triacs or directly switch low-power AC loads up to 400 V off-state. The integrated zero-crossing circuit triggers the output when the AC line voltage crosses near zero, which minimises inrush current and conducted EMI when switching resistive or lightly inductive loads.
Zero-crossing switching and dV/dt immunity
The zero-crossing circuit ensures the triac turns on only when the AC mains voltage is within approximately ±1.3 V of the zero crossing. This soft-start behaviour reduces the harmonic content of the load current and extends the life of downstream components such as relays and lamp filaments. A minimum static dV/dt rating of 1 kV/µs means the optoisolator will not falsely trigger on fast voltage transients from nearby inductive switching — a common failure mode in motor-drive and solenoid circuits without a snubber. The typical hold current of 400 µA keeps the triac latched once triggered, preventing premature dropout at low load currents. The maximum LED trigger current of 5 mA allows direct drive from standard logic or microcontroller GPIO pins through a series resistor.
Surface-mount package and reel options
Housed in a 6-SMD gull-wing package (6-SMD, Gull Wing), the MOC3043SR2M is suited for automated pick-and-place assembly.