Darlington pipe is also called composite pipe. He connected two triodes in series to form an equivalent new triode. The magnification of this equivalent transistor is the accumulation of the original two, so it is characterized by very high magnification. The function of Darlington transistor is usually to amplify very small signals in high-sensitivity amplification circuits, such as high-power switching circuits. In electronic circuit design, Darlington connection method is often used in power amplifier and regulated power supply.