Two or more electrode systems are installed in the shell of an electron tube. Each electrode system realizes its own function independently through the electron flow. This kind of electron tube is called composite tube. Compound tube refers to the use of two or more audion according to a certain law of combination, equivalent to a triode, compound tube is also known as Darlington tube. The specific connection method is as follows, taking two triode of the same polarity as an example, the front of the triode collector is connected with the back of the triode collector, the front of the triode emitter is connected with the back of the triode base, the front of the triode power is generally smaller than the back of the triode, the front of the triode base is the Darlington tube base, the back of the triode emitter is very Darlington tube emitter, the same usage as the triode, The amplification is the product of the amplification of two triodes.

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

2, drive small relay

A CMOS circuit is used to drive a high sensitivity relay through a Darlington tube, as shown in Figure 1. Inside the dotted box is the low-power NPN Darlington tube FN020.

3, drive LED intelligent display

LED intelligent display is controlled by a microcomputer, with LED matrix board as the display system,

Can be used to display various characters and patterns. The row driver and column driver in this system can adopt high β, high speed and low pressure drop composite pipe. It should be noted that the composite pipe is composed of multiple tubes and resistors, and the positive and negative resistance value of BE junction is different from that of ordinary triode when tested with a multimeter.