The 6N139 is a high-speed split Darlington photocoupler consisting of an infrared emitting diode optically coupled to a high-gain split Darlington photodetector in an 8-pin DIP package. It provides 5000 Vrms isolation voltage between input and output, with a guaranteed operating temperature range of 0°C to 70°C and support for supply voltages up to 18 V. The device features a minimum current transfer ratio of 400% at IF = 0.5 mA and VO = 0.4 V, with propagation delay times as low as 1 µs to logic low and 7 µs to logic high under high-speed switching conditions. Common applications include digital logic ground isolation, RS-232C line receivers, high common-mode noise line receivers, microprocessor bus isolation, and current loop receivers in industrial and communication systems.