Voltage regulator
From Computer History Wiki
A voltage regulator is a piece of analog circuitry which is used to provide an output at a constant voltage.
Some voltage regulators (in physical form) also include the output transistor, and thus produce the constant-voltage output directly. Others are just control circuits, and take as input the output of a power supply, and provide outputs which direct other parts of the power supply to increase or decrease the voltage of its output.