In the basic form, a bias resistor built-in transistor (BRT) is composed of either an NPN or PNP transistor and two resistors (a series base resistor (R1) and a base-emitter resistor (R2)). These three devices are housed in one package. Single (1-in-1) and dual (2-in-1) BRTs are also available. Dual BRTs are available in common-emitter, point-symmetrical, and parallel configurations with different pinouts.
The following figure shows each type of NPN BRT.
Toshiba provides a wide range of BRTs, including PNP BRTs and dual BRTs containing NPN and PNP transistors in a point-symmetrical configuration.