The semiconductor transistor is also called a crystal transistor. It can be said that it is the most important device in electronic circuits. Its main function is current amplification and switching. A triode, as its name implies, has three electrodes. The diode is made of a PN structure, while the triode is made of two PN structures. The first electrode becomes the base of the triode (indicated by the letter b). The other two electrodes become the collector (indicated by the letter c) and the emitter (indicated by the letter e). Due to different combination methods, one type is an NPN type transistor, and the other is a PNP type transistor.
There are many types of triodes, and different models have different uses. Most transistors are packaged in plastic or metal. The appearance of common transistors is as shown in the figure. The big one is very big and the small one is very small. There are two types of transistor circuit symbols: the electrode with an arrow is the emitter, the arrow pointing outward is an NPN transistor, and the arrow pointing inward is a PNP type. In fact, the direction pointed by the arrow is the direction of the current.
The triodes commonly used in electronic production include the 90×× series, including low-frequency and low-power silicon tubes 9013 (NPN) and 9012 (PNP), low-noise tubes 9014 (NPN), and high-frequency and low-power tubes 9018 ( NPN) etc. Their models are usually marked on the plastic case, and they all look the same, and they are all packaged in TO-92 standard. You can also see 3DG6 (low-frequency, low-power silicon tube), 3AX31 (low-frequency, low-power germanium tube), etc. in old-fashioned electronic products. Their models are also printed on the metal casing. There is a set of naming rules for transistors produced in our country, and it is better for electronic enthusiasts to understand them:
The 3 in the first part means a triode. The second part represents the material and structure of the device, A:
PNP type germanium material
B:
NPN type germanium material
C:
PNP type silicon material
D:
NPN type silicon material
The third part indicates the function, U: photoelectric tube
K: switching tube
X: low-frequency low-power tube
G: high-frequency low-power tube
D: low-frequency high-power Tube
A: High frequency and high power tube. In addition, the 3DJ type is a field effect tube, and the words starting with BT represent special semiconductor components.
The most basic function of a transistor is amplification. It can turn a weak electrical signal into a signal of a certain intensity. Of course, this conversion still follows the conservation of energy. It only converts the energy of the power supply into the energy of the signal. That’s all. An important parameter of the triode is the current amplification coefficient β. When a small current is applied to the base of the transistor, a current β times the injected current can be obtained on the collector, that is, the collector current. The collector current changes with the change of the base current, and a small change in the base current can cause a large change in the collector current. This is the amplification effect of the triode.
Transistors can also be used as electronic switches, and can also form oscillators when combined with other components
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