Photocoupler

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