NPN Si Phototransistors Kingbright NPN Si Phototransistors are made with NPN silicon phototransistor chips. These phototransistors are mechanically and spectrally matched to infrared-emitting LED lamps. The NPN Si phototransistors operate at a temperature range from -40°C to +85°C. These phototransistors feature a maximum collector-to-emitter voltage of 30V and an emitter-to-collector voltage of 5V. Typical applications include infrared applied systems, optoelectronic switches, and photodetector control circuits.