Transistor is a control component, is mainly used to control the current size, in order to take as an example common-emitter (signal from the base input, the output from the collector, emitter grounded), when the base voltage UB has a slight change in when the base current IB will follow a small change in base current IB under the control of the collector current IC will be a big change, the greater the base current IB, the greater the collector current IC, On the contrary, the smaller the base current, collector current is also smaller, that is, the base current controls the collector current changes. However, the changes in collector current than the changes in base current is much greater, which is the amplification transistor. Changes in IC volume and the change in the ratio of IB is called the transistor magnification β (β = ΔIC / ΔIB, Δ, said variation.), Transistor magnification β is usually in the tens to hundreds of times.

Transistor in the signal amplification, the first to enter the on-state, that is first to establish a suitable quiescent point, also known as the establishment of bias, otherwise it will enlarge distortion.

In the transistor's collector and power of the indirect one resistor, current amplification can be converted into voltage amplification: When the base voltage UB rises, IB bigger, IC is also bigger, IC voltage drop in the collector resistance RC and the more Large
B: Transistor Basics

Semiconductor Transistor, also known as transistor, you can say that it is the most important electronic circuit device. Its primary function is the role of current amplification and switching. As the name suggests transistor has three electrodes. Diode is a PN structure into, while the transistor into by the two PN structure, shared an electrode into the base transistor (indicated with the letter b). The other two electrodes as the collector (with the letter c indicated) and emitter (with the letter e indicated). Because different combinations, forming a kind of a NPN type transistor, the other is a PNP-type transistor.

Many different types of transistors, and different models have different purposes. Transistors are mostly plastic packaging or metal packaging, the appearance of common transistor shown in Figure, large lot, small small. Transistor circuit symbols, there are two: There is an arrow of the electrode is the emitter, the arrow is the NPN-type transistor outward, while the arrows move in the PNP-type. In fact the direction of arrows is the current direction.

Transistor commonly used in electronics manufacturing has 9 0 × × series, including the low-frequency low-power silicon tube 9013 (NPN), 9012 (PNP), low-noise tube 9014 (NPN), high-frequency low-power tube 9018 (NPN) and so on. Their models are generally marked on the molded case, rather like the same, are TO-92 standard packages. In the old electronic products can also see 3DG6 (low-frequency low-power silicon tube), 3AX31 (low-frequency low-power germanium tubes), etc., and their models are also printed on the metal shell. Transistors produced in our country have a naming convention, the electronic enthusiasts is best to find out:
Part 3 is expressed as transistors. The second part of said device materials and structures, A: PNP-type germanium material B: NPN-type germanium materials C: PNP-type silicon material D: NPN-type silicon material, said third part of the function, U: phototube K: switch X: low-frequency low-power tube G: high-frequency low-power tube D: low-frequency high-power tube A: high-frequency high-power tube. In addition, 3DJ type of FET, BT Heading the expression of specific semiconductor devices.

Transistor basic function is the enlarged role, it can be a weak electrical signals into a signal of a certain intensity, of course, continue to follow such a conversion of energy conservation, it is only the power to convert the energy of the signal energy Bale. There is an important parameter is the transistor current amplification factor β. When the transistor's base add a tiny current, the collector can get an injection current is β times the current, that is, the collector current. The collector current with changes in base current change, and small changes in base current can cause great changes in the collector current, which is the amplification transistor.

Transistor also can be used as electronic switches, with the other components can also constitute the oscillator.