TLP521-4 Optocoupler consist of gallium arsenideinfrared emitting diodes optically coupled to a monolithic silicon detectorperforming the function of a Zero Voltage Crossing bilateral triac driver.They are designed for use with a triac in the interface of logic systems toequipment powered from 115 Vac lines, such as solid–state relays, industrialcontrols, motors, solenoids and consumer appliances, etc.