The MOC3021SR2M is a Triac driver optocoupler in SMD package that allows low-voltage control of AC power devices. It uses infrared light inside the package to trigger a triac output, electrically isolating the low-voltage (control) side from the high-voltage (AC) side. Common uses include:

• AC load switching

• Lamp dimming

• Motor control

• Zero-crossing control (when combined with external logic)

Both are functionally identical, but:

• MOC3021SR2M is the Surface-Mount Device (SMD) version

• Standard MOC3021 is in a DIP through-hole package
  Choose based on your PCB design – SMD for compact automated assembly, DIP for prototyping.

It can trigger power triacs that control:

• AC lamps, heaters, solenoids, fans, and small motors
  Note: The MOC3021 does not include zero-cross detection, so it’s suitable for phase-angle control applications, not for precise timing across AC cycles.

• The input LED (infrared) is controlled by a microcontroller or logic circuit

• The photo-sensitive triac output responds to the light from the LED

• This turns on a power triac connected to the load, completing the AC circuit