The MJD31CT4 is a General Purpose Switch NPN Bipolar Transistor (BJT) manufactured by STMicroelectronics. It is designed for use in a wide variety of applications such as small signal switching, linear active components, and output drivers. This device is rated for a maximum collector-emitter voltage (Vce) of 30V, collector-emitter saturation voltage (Vce(sat)) of 0.5V, and a maximum collector current of 1A. It has a low saturation voltage and can switch very high currents at very low voltages making it ideal for high-speed switching applications. Furthermore, it boasts a high breakdown voltage, making it suitable for high voltage applications. It also has a high current gain, making it capable of amplifying even very weak signals.