An electronic tube is equipped with two or more electrode systems inside the shell, each of which independently performs its own function through electron flow. This type of electronic tube is called a composite tube. Composite transistor refers to the combination of two or more transistors according to a certain pattern, equivalent to one transistor. Composite transistor is also known as Darlington transistor. The specific connection method is as follows. Taking two transistors with the same polarity as an example, the front is connected to the collector of the transistor and the back is connected to the collector of the transistor. The front is connected to the emitter of the transistor and the base of the back is connected to the emitter of the transistor. The power of the front transistor is generally lower than that of the back transistor. The base of the front transistor is the Darlington transistor, and the emitter of the back transistor is the Darlington transistor. The usage is the same as that of a transistor, The amplification factor is the product of the amplification factors of two transistors.

1. Used for high-power switching circuits, motor speed regulation, and inverter circuits.

2. Drive small relays

The circuit using CMOS circuit to drive a high sensitivity relay through Darlington transistor is shown in Figure 1. The dashed box shows the low-power NPN Darlington transistor FN020.

3. Drive LED intelligent display screen

LED smart display screen is a system controlled by a microcomputer and displayed on an LED matrix board,

Can be used to display various texts and patterns. Both row and column drivers in this system can use high β、 Composite pipes with high speed and low pressure drop. It should be noted that composite transistors are composed of multiple tubes and resistors inside. When tested with a multimeter, the forward and reverse resistance values of the be junction are different from those of ordinary transistors.