Triac and SCR output optocouplers are opto-isolated devices that are used to transfer electrical signals from one circuit to another. They employ a semiconductor optical isolator, also known as an optoisolator, to electrically isolate the output from the input. A Triac and SCR output opto-coupler is a type of semiconductor switch that uses the principle of light modulation to control the on/off state of the load. The opto-coupler’s electrical input is modulated by an optical signal from the internal LED. When the LED is switched on, it activates the control signal and switches on the output. The SCR (silicon controlled rectifier) or Triac (triode for alternating current) then act as a switch and either blocks or allows the flow of current. The opto-coupler provides a very high level of electrical isolation between two circuits, allowing sensitive circuits to be protected against damage due to high voltage or current transients.