The PT91-21B/TR7 is an infrared phototransistor manufactured by Everlight. It is a semiconductor photo-detector which uses a reverse biased junction when exposed to light to convert light pulses into electrical signals. The detector works based on a light-activated circuit, meaning that it will trigger when it is exposed to infrared light of specific frequencies, for example, the infrared light emitted by a remote control. The PT91-21B/TR7 is encapsulated in a black plastic package and is hermetically sealed for use in severe environments. It offers excellent and consistent operation over the entire operating temperature range of -40°C to + 85°C and offers 3500V ESD and 15kV ESD as an additional protection. The detector is suitable for use in a variety of applications such as remote control, computer systems, toys, and automotive vehicles.