||The basic function of a Photo Coupler is that it ensures total electronic isolation, including potential isolation (as in the case of transformer) in an electrical circuit. Devices of the Photo Coupler family include Photo Transistor, Photo Darlington Transistor High speed Photo coupler and OPIC. These devices have the characteristics of excellent isolation, high CTR, compact package, high-speed operation, low decay and unit control function not being influenced by field effects. They are most suitable to be used for microelectronics, data processing and telecommunication system. Due to their high safety features, they are particularly suitable for use in switching mode power supply units.