Photocoupler

A signal transmission circuit composed of a light-emitting element on the input side and a light-receiving element on the output side. When an input signal is applied to the light-emitting element, it emits light and sends it to the light-receiving element. The light-receiving element detects the light and outputs an output signal. Since the transmission of on/off signals between the input and output sides is performed via light, the primary and secondary sides can be completely insulated and physically separated. It is often used to protect the secondary side when handling high voltage on the primary side and can also be used as a noise filter.