An optocoupler is used as input interface. It is a function of insulation and adaptation. A relay is used as output interface. It is voltage adaptation and it allows more power. A relay operating on the principle of opto-isolation, i.e. there is no direct or hardwire connection between the controller and the relay. And because there is no hardwire, the controller will remain protected against the high voltages that might harm the controller.
The relay output is an electrical switch mechanicaly opening or closing. The opto-isolator uses light to communicate with electrical isolation from input to output, no moving parts and at high speeds. A power relay module is an electrical switch that is operated by an electromagnet. The electromagnet is activated by a separate low-power signal from a micro controller. When activated, the electromagnet pulls to either open or close an electrical circuit.
The optocoupler is the portal between the trigger and the switching circuit. The input trigger is applied to the LED of the opto which illuminates and makes the photo-transistor conduct. The voltage from the photo-transistor passes across the collector to the emitter and finally reaches the triac’s gate to operate it.
