The OPI120 is an optically coupled isolator containing both an infrared emitting diode and an NPN silicon phototransistor. The phototransistor has the base contact brought out to allow the user to externally turn the output phototransistor off or pre-bias it to allow faster data transfer. The part is sealed in a high dielectric plastic housing. The LED and sensor are in hermetically sealed packages. This device is designed for applications that require high voltage isolation (up to 15,000 volts) between the input and output over a wide range of temperatures as in industrial and medical equipment.