The FOD817A is a phototransistor optocoupler from the FOD817 series, supplied in a 4-pin dual in-line package. It is designed to provide electrical isolation between its input and output circuits. This specific model is binned for a Current Transfer Ratio (CTR) between 80% and 160% when tested with a 5 mA forward current. Key electrical characteristics include a guaranteed minimum collector-emitter breakdown voltage of 70 V and a low collector-emitter saturation voltage, typically 0.1 V. The FOD817A is commonly used in applications such as power supply regulators, digital logic inputs, and microprocessor inputs where signal isolation is critical.