Bipolar transistors are controlled using the base current. However, because of the voltage across the base, the emitter path is highly temperature dependent. In most applications, a series of resistor is required to keep the base current at the desired level, thereby ensuring the stable and safe operation of the transistor. Resistor-equipped transistors (RETs) combine single and dual bipolar transistors with the bias resistors which are integrated on the same die. Because these internal resistors have higher tolerances than commonly used external resistors, RETs are suitable for switching applications where the transistor operates in either the on or off-state. That is why these parts are also called digital transistors.