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Triode principle-the most popular statement I have ever seen

Triode principle

To understand the amplification function of triode, remember one thing: it will not produce energy for no reason, so triode will definitely not produce energy.

But the power of transistor is that it can control large current through small current.

The principle of amplification is to control large static DC through small AC input.

Suppose the triode is a dam. The strange thing about this dam is that there are two valves, a big valve and a small valve. Small valves can be opened by manpower, while large valves are relatively heavy and cannot be opened by manpower, so they can only be opened by hydraulic power of small valves.

So the usual workflow is that whenever water is released, people will open a small valve and a stream will trickle out. This trickle will touch the switch of the big valve, and the big valve will open accordingly, and the turbulent river will flow down.

If the opening of a small valve changes constantly, so will the large valve. If it can be changed strictly in proportion, then perfect control is completed.

Here Ube is a small water flow, Uce is a large water flow, and people are input signals. Of course, if the proportion of water flow is current, it will be more accurate, because transistors are current control elements after all.

If one day, the weather is very dry and the river is gone, it is that the big water is empty there. At this time, the administrator opened the small valve. Although the small valve still hit the big valve as usual and left it open, there was no water flow, so there was no water flow. This is the cutoff region of the triode.

The saturated area is the same, because the river has reached a great level at this time, and the size of the valve opened by the administrator is useless. If the valve is not opened, the river will burst by itself, which is the breakdown of the diode.

In the analog circuit, the general valve is half-open, and the output water flow is determined by controlling its opening. When there is no signal, water will flow, so there will be power consumption when it is not working.

In the digital circuit, the valve is in the open or closed state. When not working, the valve is completely closed and does not consume electricity.

The metaphors about saturation zone and cutoff zone behind you are problematic, but you must know these principles, hehe.

Cut-off area: it should be that the opening of the small valve is not enough (yes

Saturation zone: the small valve should be opened too wide (be > Uce & gtUon) to release it in the large valve.

The current has reached its limit. At this time, if you increase the opening of the small valve (Ib), the water flow from the large valve will not increase (Ic will not change); But you turned down the small valve (lowering Ube until UBE)

Linear region: that is, the water flow is in an adjustable state.

Breakthrough area: For example, if there is water in a reservoir, the water level is too high (corresponding to high Vce), resulting in a gap and water flowing out. And with the opening of the small valve, the breakdown voltage becomes lower, which means it is easier to break down. ///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

Terminology description

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I. Triode

Triode is two PN junctions living on a piece of semiconductor material. Because each semiconductor transistor has two PN junctions, it is also called bipolar junction transistor.

A triode actually connects two diodes with the same electrode. It is a current control element. Using the special structure of narrow base region and the diffusion and recombination of carriers, the control of base current to collector current is realized, which makes the transistor have stronger control ability. According to the internal structure, triode can be divided into PNP tube and NPN tube, and the two tubes can be connected in a certain way to form a pair of tubes, which has stronger working ability. According to the power consumption of triode, it can be divided into low power triode, medium power triode and high power triode.

Second, the role and application

Triode has the function of amplifying current signal and switching control. Therefore, triode can be used to amplify signals and control the on-off of current. Transistors can be seen in power supply, signal processing and other places, and integrated circuits are also made up of many transistors connected in a certain circuit form, which has certain uses. Triode is the most important current amplifier.

Three. Important parameters of triode

1, β value

β value is the most important parameter of triode, because β value describes the amplification ability of triode to current signal. The higher the β value, the stronger the amplification ability of small signals, and vice versa; However, the β value cannot be made very large, because it is too large, and the performance of the transistor is unstable. Generally, the β value should be selected between 30 and 80. Generally speaking, the β value of triode is not a specific reference value, and generally changes slightly with the working state of the element.

2. Interelectrode reverse current

The smaller the reverse current between the electrodes, the higher the stability of the triode.

3, triode reverse breakdown characteristics:

The triode consists of two PN junctions. If the reverse voltage exceeds the rated value, it will be broken down like a diode, thus reducing performance or permanently damaging it.

4. Operating frequency

The β value of triode only remains unchanged within a certain working frequency range. If they exceed the frequency range, they will drop sharply with the increase of frequency.

Fourth, classification

According to different amplification principles, triodes can be divided into bipolar junction transistors (BJT) and unipolar transistors (MOS/MES type: metal oxide semiconductor or metal semiconductor). BJT has two kinds of carriers, but only one MOS carrier conducts electricity. BJT is generally a current control device, while MOS type is generally a voltage control device.

Verb (abbreviation of verb) is used.

Transistors in digital circuits are mostly used as switches, as long as the transistors work in the saturation region and the cutoff region!

Formula for measuring and judging triode

Distinguishing the tube type and pin of triode is a basic skill for beginners of electronic technology. In order to help readers master the method of measuring and judging quickly, the author summarizes four formulas: "three inverses, finding the bottom;" PN junction, fixed tube type; In the direction of arrow, large deflection; Not sure, move your mouth. " Let's explain sentence by sentence.

One, three, turn it upside down and find the base.

As we all know, triode is a semiconductor device with two PN junctions. According to the different connection modes of the two PN junctions, they can be divided into two transistors with different conductivity types: NPN type and PNP type. Figure 1 shows their circuit symbols and equivalent circuits.

To test the triode, use the ohm range of the multimeter, and select the R× 100 or R× 1k range. Fig. 2 describes the equivalent circuit of ohm range of multimeter. As can be seen from the figure, the red stylus is connected to the negative electrode of the battery in the instrument, and the black stylus is connected to the positive electrode of the battery in the instrument.

Suppose we don't know whether the transistor under test is NPN or PNP, and we can't tell which electrode each pin is. The first step in testing is to determine which pin is the base. At this time, we take any two electrodes (for example, these two electrodes are 1, 2), measure the positive and negative resistance with two probes of a universal ammeter upside down, and observe the deflection angle of the pointer; Then, take two electrodes of 1 and 3 and two electrodes of 2 and 3, measure their forward and reverse resistances respectively, and observe the deflection angle of the pointer. In these three back tests, there must be two similar results: that is, in the back test, the first deflection of the watch hand is large and the first deflection is small; The remaining time must be that the deflection angle of the pointer before and after reverse measurement is very small, and this time the unmeasured needle is the base we are looking for (see figure 1 and figure 2).

Second, PN junction, fixed tube type

After finding the base of the transistor, we can determine the conductivity type of the transistor according to the PN junction direction between the base and the other two electrodes (Figure 1). Touch the base with the black pen of the multimeter, and touch either of the other two electrodes with the red pen. If the deflection angle of the multimeter pointer is large, it means that the triode under test is an NPN tube. If the deflection angle of the instrument pointer is small, the tube under test is PNP type.

Third, in the direction of the arrow, large deflection.

Find out the base B. Which of the other two electrodes is the collector C and which is the emitter E? At this point, we can determine the collector c and emitter e by measuring the penetration current ICEO.

(1) For the NPN transistor, the circuit for measuring the penetration current is shown in Figure 3. According to this principle, the positive and negative resistances Rce and Rec between the two poles are measured with the black and red probes of the multimeter inverted. Although the deflection angle of the multimeter pointer measured twice is very small, there will always be a slightly larger deflection angle after careful observation. At this time, the current flow direction must be: black probe →c pole →b pole →e pole → red probe, and the current flow direction is completely consistent with the arrow direction (forward arrow) in the triode symbol.

(2) For PNP triode, the reason is similar to NPN triode, and its current flow direction must be: black contact →e electrode →b electrode →c electrode → red contact, and its current flow direction is also consistent with the direction of the arrow in the triode symbol, so the black contact must be connected to the emitter E and the red contact must be connected to the collector C (see Figure 1 and Figure 3).

Fourth, move your mouth if you can't measure it.

If the deflection of the measuring pointer before and after inversion is too small to distinguish during the measurement process of "following the arrow, it will be" moving ". The specific method is: in the two measurements of "large deflection in the direction of arrow", hold the connection between the two pens and the pin with both hands, and hold the base B with the mouth (or tongue), and still use the discrimination method of "large deflection in the direction of arrow" to distinguish the collector C from the emitter E, in which the human body is used as a DC bias resistor, which makes the effect more obvious.

Classification of semiconductor triodes

There are many kinds of semiconductor triodes, also known as bipolar transistors. According to the structure and technology, there are PNP and NPN types; According to the classification of manufacturing materials, there are germanium tubes and silicon tubes; According to the working frequency, there are low frequency tubes and high frequency tubes; Generally, low-frequency tubes are used to process circuits with frequencies below 3MHz, and the working frequency of high-frequency tubes can reach several hundred MHz. According to the allowable power consumption, there are low power tubes and high power tubes; Generally, the rated power consumption of small power tubes is below 1W, while the rated power consumption of large power tubes can reach tens of watts or even more. See Figure 2.5. 1 for the appearance of common semiconductor triodes.

Main parameters of semiconductor triode

* * * Emission current amplification factor β. β value is generally 20 ~ 200, which is the most important parameter to characterize the current amplification of triode.