There are mainly two types of three terminal voltage regulators: one with a fixed output voltage, called a fixed output three terminal voltage regulator, and the other with an adjustable output voltage, called an adjustable output three terminal voltage regulator. The basic principle is the same, and both use a series type voltage regulator circuit. In linear integrated voltage regulators, due to the fact that three terminal regulators only have three output terminals, they have the advantages of fewer external components, convenient use, stable performance, and low cost, and are therefore widely used.