Understand the structure and classification of transistors

Understand the structure and classification of transistors

The transistor is composed of two PN structures, divided into three layers, according to the order of p-type and n-type arrangement, can be divided into NPN-type and PNP-type two categories. According to the different materials used, transistors can be divided into NPN-type germanium diodes and NPN-type silicon diodes, PNP-type germanium diodes and PNP type silicon diodes.

Both types of transistors are divided into base region, emission region, and collector region, and the electrodes drawn from them are called base (B), emitter (E), and collector (C). The knot between the base area and the emission area is called the emission node; The junction between the base area and the collector area is called the collector junction. The difference between npn and pnp symbols is the direction of the arrow of the emitter.

The internal structure of the transistor is characterized by: high concentration of impurities in the emission area, that is, high polytron concentration and large volume; The base region is thin and the concentration of impurities is extremely low; The volume of the collector area is large, and the concentration of impurities is lower than that in the emission area. This is the internal condition under which the transistor has an amplification effect of current.