Principle and characteristics of transistor 1

1、 The current amplification principle of transistor

There are two types of transistors based on their materials: storage transistors and silicon transistors.

And each of them has two structural forms, NPN and PnP, but the most commonly used are silicon NPN and PnP transistors. Except for the power polarity, their working principles are the same. The following only introduces the current amplification principle of NPN silicon transistors.

When manufacturing a transistors, it is consciously necessary to make the majority carrier concentration in the emitter region higher than that in the base region. At the same time, the base region should be made very thin, and the impurity content should be strictly controlled. In this way, once the power is turned on, due to the correct emitter junction, the majority carriers (electrons) in the emitter region and the majority carriers (control holes) in the base region can easily cross the emitter structure and diffuse in opposite directions. However, because the concentration of the former is higher than that of the latter, the current passing through the emitter junction is basically an electron current, which is called the emitter current Ie. Due to the thin base region and the reverse bias of the collector junction, most of the electrons injected into the base region cross the collector junction and enter the collector region, forming a collector current. Ic, leaving only a small (1-10%) number of electrons to recombine with the holes in the base region. transistorsThe recombined holes in the base region are supplied by the base power source Eb By supplementing the memory, the base current Ibo was formed. According to the principle of current continuity, Ie=Ib+Ic means that by adding a small Ib to the base, a larger Ic can be obtained at the collector, which is called current amplification. Ic and Ib maintain a certain proportional relationship, that is, β 1=Ic/Ib. In the formula, β - is called the DC amplification factor, and the ratio of the change in collector current △ Ic to the change in base current △ Ib is: β=△ Ic/△ Ib. In the formula, β - is called the AC current amplification factor. Due to the small difference in values between β 1 and β at low frequencies, sometimes for convenience, the two are not strictly distinguished. The value is about tens to hundreds. A transistor is a current amplification device, but in practical use, it often utilizes the current amplification effect of a transistor, which is converted into voltage amplification effect through resistance.transistors