FOD819x Output Optocouplers onsemi FOD819x Output Optocouplers consist of Gallium Arsenide (GaAs) infra-red emitting diode in a 4-pin Dual-In-Line Package (DIP). The photodetectors are integrated with a base-to-emitter resistor. The FOD819x output optocouplers are designed to be an improved replacement to the FOD817 optocouplers when high-speed performance is required in isolated data signal transmission. Typical applications include digital logic inputs, microprocessor inputs, power supply monitors, twisted pair line receivers, and telephone line receivers.