Triode is one of the basic components of semiconductor, which has the function of current amplification and is the core component of electronic circuit. The triode is composed of two PN junctions, which are very close to each other on the semiconductor substrate. Two PN junctions divide the whole semiconductor into three parts, the middle part is the base region, and the two sides are the emitter region and the collector region. The arrangement is PNP and NPN.
Chinese name
Triode
Foreign name
Bipolar junction transistor
Another name
crystal triode
Time of invention
1947
material
semiconductor
quick
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Development history working principle product classification product parameter judgment type structure type product function working state product judgment amplifier circuit product symbol product naming selection replacement judgment formula
Basic explanation
Triode [1] (also known as transistor) is just a general term for three-pin amplification devices in Chinese. We often say that triodes may be several devices as shown in the figure.
It can be seen that although they are all called triodes, the expressions in English are quite different. The word triode is actually a pictographic word unique to China people.
"Triode" is the only English translation of "Triode" in English-Chinese dictionaries, which is related to the first appearance of electronic triode, and it is the original object referred to by the word triode in the real sense. Other devices called triodes in Chinese cannot be translated into triodes in practical translation.
Triode (commonly known as a kind of electron tube)
Bipolar transistor BJT (bipolar junction transistor)
J-type field effect transistor junction gate field effect transistor (FET)
MOS FET (metal oxide semiconductor field effect transistor) is the English full name.
V-groove field effect transistor VMOS (vertical metal oxide semiconductor)
Note: All three seem to be field effect transistors. In fact, metal oxide semiconductor field effect transistor and V-channel field effect transistor are both unipolar structures, corresponding to bipolar, so they can also be collectively referred to as unipolar junction transistors.
Among them, J-FET is non-insulated FET, MOS FET and VMOS are insulated FET.
VMOS is a new power transistor with high current and high amplification (cross-channel) based on MOS. The difference is that the V-groove is adopted, which greatly improves the amplification factor and working current of MOS transistor, but also greatly increases the input capacitance of MOS transistor. It is a high-power improved product of MOS transistor, but its structure has been very different from the traditional MOS transistor. VMOS is just an enhancement, and there is no depletion MOS tube unique to MOS.
Development history
1947 12.23, Bell Laboratory, Murray Hill, New Jersey, USA. Three scientists-Dr. Bardeen, Dr. Brighton and Dr. shockley-are doing experiments nervously and methodically. They are conducting experiments to amplify sound signals with semiconductor crystals in conductor circuits. Three scientists were surprised to find that one part of the tiny current through the device they invented can actually control the much larger current through the other part, thus producing amplification effect. This device is an epoch-making achievement in the history of science and technology-transistor. Because it was invented on Christmas Eve, it has such a great influence on people's future life, so it is called "Christmas gift to the world". These three scientists won the 1956 Nobel Prize in Physics.
[2] The new research found that the P-N structure of semiconductor refrigeration can be formed by depositing a layer of corresponding material outside the substrate at the electron outflow end of the transistor, because the electron energy level of N material is low and that of P material is high, and electrons need to absorb heat from the substrate when flowing, which provides a good way for the transistor core to dissipate heat. Because the heat taken away will be directly proportional to the current, the industry also calls this "electronic blood" cooling technology. According to the polarity position of new materials, new refrigeration triodes are called N-PNP or NPN-P respectively.
Transistors promoted and brought about the "solid-state revolution", which in turn promoted the semiconductor electronics industry on a global scale. As the main component, it was first applied to communication tools in time and widely, and produced great economic benefits. Because transistors have completely changed the structure of electronic circuits, integrated circuits and large-scale integrated circuits have appeared, making high-precision devices such as high-speed electronic computers a reality.
principle of operation
theoretical basis
Transistors (hereinafter referred to as triodes) are divided into germanium tubes and silicon tubes according to materials. They have two structural forms, NPN and PNP respectively, but the most commonly used are silicon NPN and germanium PNP triodes (where n stands for negative in English, N-type semiconductors add phosphorus to high-purity silicon to replace some silicon atoms, which generates free electron conduction under voltage stimulation, and P stands for positive, that is, boron is added to replace silicon, resulting in a large number of hole conduction). They work on the same principle except the polarity of the power supply. The following only introduces the current amplification principle of NPN silicon tube.
For NPN tube, it consists of two N-type semiconductors with a P-type semiconductor in the middle. The PN junction formed between emitter and base is called emitter junction, and the PN junction formed between collector and base is called collector junction. These three leads are called emitter e (emitter), base b (base) and collector c (collector). As shown on the right
When the potential at point B is several volts higher than that at point E, the emitter junction is in a forward bias state, while when the potential at point C is several volts higher than that at point B, the collector power supply Ec is higher than the base power supply Eb.
When manufacturing triodes, consciously make the concentration of majority carriers in the emitter region greater than that in the base region, and at the same time make the base region very thin, and strictly control the impurity content, so that once the power supply is turned on, the majority carriers (electrons) in the emitter region and the majority carriers (holes) in the base region can easily diffuse across the emitter junction, but because the concentration base of the former is greater than that of the latter, the current passing through the emitter junction is basically an electron flow.
Because the base region is thin and the collector junction is reversely biased, most of the electrons injected into the base region pass through the collector junction and enter the collector region to form a collector current Ic, and only a few electrons (1- 10%) recombine in the base region holes, which are supplemented by the base region power supply Eb to form the base region current Ibo. According to the principle of current continuity:
Ie=Ib+Ic
That is to say, if a small Ib is added to the base, a large Ic can be obtained on the collector, which is called current amplification, and Ic and Ib maintain a certain proportional relationship, namely:
β 1=Ic/Ib
Where: β 1- is called DC magnification.
The ratio of collector current change △Ic to base current change △Ib is:
β= △Ic/△Ib
In the formula, β-is called AC current amplification factor. Because there is little difference between β 1 and β at low frequencies, sometimes for convenience, there is no strict distinction between them, and the β value is about tens to more than 100.
α 1=Ic/Ie(Ic and Ie are currents in the DC path).
Among them, α 1, also known as DC amplification factor, is generally used in * * * base configuration amplifier circuits to describe the relationship between emitter current and collector current.
α =△Ic/△Ie
α in the expression is the base current magnification of AC * * * * Similarly, when small signal is input, there is little difference between α and α 1.
For the two magnifications that describe the current relationship, the following relationship exists.
The current amplification function of triode is actually to control the huge change of collector current by using the small change of base current. [3]
Triode is a kind of current amplification device, but in practical use, the current amplification of triode is often converted into voltage amplification through resistance.
Amplification principle
1. The emitter emits electrons to the base region.
The power supply Ub is applied to the emitter junction through the resistor Rb, and the emitter junction is positively biased, and the majority carriers (free electrons) in the emitter region continuously pass through the emitter junction and enter the base region, forming the emitter current Ie. At the same time, the majority carriers in the base region also diffuse to the emitter region, but because the concentration of majority carriers is much lower than that in the emitter region, this current can be ignored, so it can be considered that the emitter junction is mainly an electron current.
2. Diffusion and recombination of electrons in the base region
After the electrons enter the base region, they first concentrate near the emitter junction, and gradually form the electron concentration difference. Under the effect of concentration difference, the electron current diffuses to the collector junction of the base region and is pulled into the collector region by the electric field of the collector junction, forming a collector current ic. A small number of electrons (because the base region is very thin) recombine with the hole in the base region, and the ratio of diffused electron current to compound electron current determines the amplification ability of the transistor.
3. The collector region collects electrons.
Because the reverse voltage applied to the collector junction is very large, the electric field force generated by this reverse voltage will prevent the electrons in the collector region from diffusing to the base region, and at the same time pull the electrons diffused near the collector junction into the collector region to form the collector main current Icn. In addition, the minority carriers (holes) in the collector region will also drift and flow to the base region to form reverse saturation current, which is expressed by Icbo, and its value is very small, but it is extremely sensitive to temperature.
product classification
A. According to materials: silicon tube and germanium tube.
B. according to the structure: NPN, PNP. As shown in the figure:
C. According to functions: switch tube, power tube, Darlington tube, photosensitive tube, etc.
D. According to power: low power tube, medium power tube and high power tube.
E. According to working frequency: low frequency tube, high frequency tube and overclocking tube.
F. According to structural technology, it is divided into alloy pipe and flat pipe.
G. According to the installation method: plug-in triode and patch triode.
Product parameter
characteristic frequency
When f= fT, the transistor completely loses its current amplification function. If the operating frequency is greater than fT, the circuit will not work normally.
FT is called the gain bandwidth product, that is, fT=βfo. If the operating frequency fo and the high frequency current amplification of the current triode are known, the characteristic frequency fT can be obtained. With the increase of working frequency, the magnification will decrease. FT can also be defined as the frequency when β= 1
Voltage/current
This parameter can be used to specify the voltage and current range of the electron tube.
hFE
Current magnification.
VCEO
The reverse breakdown voltage of collector and emitter represents the saturation voltage at critical saturation.
pcm
Maximum allowable dissipation power.
parcel
Specifies the external shape of the pipe. If all other parameters are correct, different packages will make it impossible to assemble on the circuit board.
Judging type
Judging the pin position of the triode, there are two packaging arrangements for the pin position of the triode, such as the right figure: the triode is a junction resistance device, and its three pins have obvious resistance data. During the test (taking the digital multimeter as an example, red pen+,black pen-), we switch the test gear to the diode gear (buzzer gear), as shown in the right figure: the base (b) of the normal NPN structure triode is opposite to the collector (b). The reverse resistance of the base (B) of normal PNP structure to the collector (C) and emitter (E) is 430 Ω-680 Ω, and the forward resistance is infinite. When there is no bias current, the resistance from collector C to emitter E is infinite. The test resistance from base to collector is approximately equal to the resistance from base to emitter. Generally, the test resistance of base to collector is about 5-100Ω smaller than that of base to emitter (high-power transistor is obvious). If this value is exceeded, the performance of the component has deteriorated. Please don't use it again. If misused in the circuit, the working point of the whole or part of the circuit may deteriorate, and this component may be damaged soon. High-power circuits and high-frequency circuits have obvious reactions to this inferior component.
Although the packaging structure is different, it has the same function and performance as other types of lamps with the same parameters, and different packaging structures are only needed for specific use occasions in circuit design.
It should be noted that some manufacturers produce some non-standard components, for example, the normal pin position of C945 is BCE, but the pin position arrangement of this component produced by some manufacturers is EBC, which will lead those careless workers to put new components into the circuit without testing, which will lead to the circuit not working, and even burn out related components, such as the switching power supply used in TV sets.
In our common multimeter, test the pin arrangement diagram of triode:
Suppose one electrode of the triode is the "base", connect the black stylus to the assumed base, and then connect the red stylus to the other two electrodes in turn. If the resistance measured twice is very large (about several k to several tens k) or very small (several hundred k to several k), repeat the above measurement for the contact pin. If the measured two resistances are opposite (both small or large), it can be determined that the assumed cardinality is correct. Otherwise, assuming that the other pole is the "base", repeat the above test to determine the base.
After the base is determined, connect the black stylus to the base and the red stylus to the other two electrodes. If the measured resistance is small, the transistor is NPN, otherwise it is PNP.
Judge the collector c and emitter e, taking NPN as an example:
Connect the black contact pin to the hypothetical collector C and the red contact pin to the hypothetical emitter E, hold the B and C poles by hand, read the resistance values of C and E shown in the table, then connect the red and black contact pins backwards and retest. If the resistance of the first time is less than the resistance of the second time, the original hypothesis holds.
structure type
A transistor consists of two very close PN junctions on a semiconductor substrate. Two PN junctions divide the whole semiconductor into three parts, the middle part is the base region, and the two sides are the emitter region and the collector region. The arrangement is PNP and NPN.
The corresponding electrodes are led out from three areas, namely, the base B, the emitter E and the collector C.
The PN junction between emitter and base is called emitter junction, and the PN junction between collector and base is called collector junction. The base region is thin, while the emitter region is thick and the impurity concentration is high. The emitter region of PNP triode "emits" holes, and its moving direction is consistent with the current direction, so the emitter arrow is inward; The emitter of NPN transistor "emits" free electrons, which move in the opposite direction to the current direction, so the emitter arrow is outward. The emitter arrow points to the conduction direction of PN junction under DC voltage. There are two kinds of silicon transistors and germanium transistors: PNP and NPN.
Packaging form and pin identification of triode