Electronic technology is an emerging technology that began to develop in the late 19th and early 20th centuries. It has developed most rapidly in the 20th century and has become the most widely used, becoming an important symbol of modern science and technology development. Into the 21st century, people) electronic computers and the Internet as a symbol of the information society. High-tech is faced with the unprecedented development of social productivity and economy through the application of microelectronics (semiconductor and integrated circuits as the representatives. Modern electronic technologies in defense, science, industry, medicine, communications (information processing, transmission, and communication) ) and cultural life have played an enormous role in various fields. In the current world, electronic technology is everywhere: radios, color TVs, audio, DVDs, mobile phones, electronic watches, digital cameras, microcomputers, industrial production lines for mass production, The Internet, robots, space shuttles, cosmic detectors, it can be said that people now live in the electronic world and they cannot live without it one day.
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Here we only introduce bipolar transistors.
1. Structure of Bipolar Transistor (BJT)
BJT is a device that combines two PN junctions through a certain process. Due to the mutual influence of PN junctions, BJT exhibits a characteristic different from that of a single PN junction and has a current amplification effect. BJT is often called a transistor.
2.BJT classification
There are many types of transistors. According to the frequency, there are high-frequency and low-frequency tubes. According to the power, there are low-power tubes, medium-power tubes and high-power tubes. According to the semiconductor materials, there are silicon tubes and helium tubes. There are NPN triodes and PNP triodes; in the form of seals, there are in-line triodes, patch triodes and so on.
3. Triode rules
For example: 3DG18
Model Code Model Code
KC846A 1A KC847C 1G
KC846B 1BW KC848A 1J
KC847A 1E KC848B 1K
KC847B W1F KC848C 1L
4. The symbol of the transistor
5. Several common transistors: low power transistors, low power transistors, SMD transistors, in-line transistors
6. Three pins of the transistor: C: Collector, B: Base, E: Emitter.
7. Triode's three working states: off state, zoomed state, and saturation state. 
