This paper summarizes the two working principles of triode-knowledge chapter
Date：2021-04-22Viewed：2091
Original title: Working principle of triode
Triode, the full name should be semiconductor triode, also known as bipolar transistor and crystal triode, is a semiconductor device for controlling current. Its function is to amplify weak signals into electrical signals with larger amplitude, and it is also used as a contactless switch. Triode is one of the basic components of semiconductor, which has the function of current amplification and is the core component of electronic circuit. Triode is formed on a semiconductor substrate with two PN junctions which are very close to each other. The two PN junctions divide the whole semiconductor into three parts, with the substrate in the middle and the emitter and collector on both sides, with PNP and NPN as the arrangement mode. Then the working principle of triode is divided into theoretical principle and amplification principle, and the working principles of these two triodes are analyzed as follows.
Working principle of triode
Introduction: According to materials, it can be divided into crystal triode (hereinafter referred to as triode) and silicon triode. Each has NPN and PNP structures, but the most commonly used transistors are silicon NPN and germanium PNP, in which N stands for Negative. N-type semiconductor adds phosphorus to high-purity silicon instead of silicon atoms, which produces free electron conduction under voltage stimulation, and P means positive. Adding boron instead of silicon is beneficial to conduction. Their working principles are the same except that the polarity of power supply is different. The current amplification principle of NPN silicon tube is only introduced below.
First, the theoretical principle
For NPN tube, a P-type semiconductor is sandwiched between two N-type semiconductors. The PN junction formed between emitter and base region is called emitter junction, and the PN junction formed between collector and base region is called collector junction. The three leads are called emitter e, base b and collector c. As shown in the following figure
When the potential at point B is a few volts higher than that at point E, the emitter junction is in deviation state, and when the potential at point C is a few volts higher than that at point B, the collector power Ec is higher than the base power Eb.
In the manufacture of triodes, the concentration of most carriers in the emitter region is consciously greater than that in the base region, while the base region is thin and the impurity content is strictly controlled. In this way, once the power supply is turned on, the majority carriers (electrons) in the emitter region and the majority carriers (holes) in the base region easily diffuse to each other 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, which is called emitter electron flow.
Due to the thin base region and the bias of the collector junction, most of the electrons injected into the base region cross the collector junction and enter the collector region to form collector current Icn, leaving only a few (1-10%) electrons to recombine in the holes in the base region, and the recombined holes in the base region are replenished by base power Eb, thus forming base current Ibn. According to the principle of current continuity, Ie=Ib+Ic is obtained
That is to say, if a small Ib is added to the base, a larger Ic can be obtained on 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 1-is called DC magnification, and the ratio of the variation of collector current △Ic to the variation of base current △Ib is β = △ IC/△ IB; In the formula, β-is called AC current magnification. Because there is little difference between β1 and β at low frequency, sometimes, for convenience, there is no strict distinction between them, and the value of β is about tens to more than one hundred. α1=Ic/Ie(Ic and Ie are the magnitude of current in DC path), where α1 is also called DC amplification factor, which is generally used in common-base configuration amplification circuit and describes the relationship between emitter current and collector current. α =△Ic/△Ie； α in the expression is the amplification factor of AC common base current. In the same way, there is little difference between α and α1 when small signal is input.
For the two magnifications describing the current relationship, there is the following relationship, as shown in the following figure
In fact, the current amplification function of triode is to control the large change of collector current by using the small change of base current. Moreover, the triode is a kind of current amplifying device, but in practical use, the current amplifying function of the triode is often converted into voltage amplifying function through resistors.
Second, the principle of amplification
(1) the emission region emits electrons to the base region
Power Ub is added to the emitter junction through resistor Rb, and the emitter junction is forward biased. Most carriers (free electrons) in the emitter region continuously cross the emitter junction and enter the basic region, forming emitter current Ie. At the same time, most carriers in the base region also diffuse to the emitter region, but because the concentration of most carriers is much lower than that in the emitter region, it can be considered that the emitter junction is mainly electron flow;
(2) Diffusion and recombination of electrons in the base region
After entering the basic region, electrons are first concentrated near the emitter junction, and gradually form an electron concentration difference. Under the action of the concentration difference, the electron flow is promoted to diffuse to the collector junction in the basic region, and is pulled into the collector region by the collector junction electric field to form a collector current Ic. There is also a small number of electrons (because the base region is very thin) which recombine with the holes in the base region, and the ratio of diffused electron flow to compound electron flow determines the amplification ability of the triode;
(3) collecting electrons in the collector area
Because the collector junction and the voltage are large, the electric field force generated by the voltage prevents the electrons in the collector region from diffusing to the base region, and pulls the electrons diffused near the collector junction into the collector region to form the collector main current Icn. In addition, minority carriers (holes) in the collector region will drift and flow to the base region to form saturation current. Icbo said that its value is very small, but it is extremely sensitive to temperature.
The above contents mainly introduce two working principles of triode.
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Label: working principle of triode, what is working principle of triode and introduction of working principle of triode
