moc3021 optocoupler

MOC3021 is triac driven a zero-crossing optocoupler. Optocoupler is made of light emitting and light sensing devices with no internal connection except light bean. The optoisolators allow two circuits to exchange signal without making any electrical connection.

This device works on principle that light is proportional to signal and and signal is transferred to photo transistor.

Opto-isolators or Opto-couplers, are made up of a light emitting device, and a light sensitive device, all wrapped up in one package, but with no electrical connection between the two, just a beam of light. The light emitter is nearly always an LED.

The light sensitive device may be a photodiode, phototransistor, or more esoteric devices such as thyristors, TRIACs etc.