Transistor Device and applied by simple language. Principles of operation of the transistor. The difference in the principle of transistors with various structures

Regardless of the principle of operation, the semiconductor transistor contains single crystal from the main semiconductor material, most often it is silicon, germanium, arsenide gallium. The main material added, alloying additives for the formation of P-n transition (transitions), metal conclusions.

The crystal is placed in a metal, plastic or ceramic housing, to protect against external influences. However, there are also inapproprous transistors.

The principle of operation of the bipolar transistor.

The bipolar transistor can be either P-N-P, or N-P-N, depending on the alternation of the semiconductor layers in the crystal. In any case, the conclusions are called - base, collector and emitter. The semiconductor layer corresponding to the base is concluded between the layers of the emitter and the collector. It has a fundamentally very small width. The charge carriers move from the emitter through the base - to the collector. The condition of current occurrence between the collector and the emitter is the presence of free media in the base area. These carriers penetrate there when the current emitter base occurs. The cause of which may be the difference of voltage between these electrodes.

Those. - For the normal operation of the bipolar transistor, the presence of a certain minimum level is always necessary for the signal amplifier, to shift the emitter-base transition in the forward direction. Direct displacement of the transition base-emitter Output transistor, sets the so-called - operating point of the mode. To harmonize voltage and current signal, the mode is used - A. In this mode, the voltage between the collector and the load is about equal to the half of the supply voltage - ie, the output resistance of the transistor and the load is approximately equal. If you submit now to the database transition - emitter AC signal, the emitter resistance - the collector will change, graphically repeating the input signal form. Accordingly, the same will occur with the current through the emitter to the collector flowing. And the amplitude of the current will be more than the amplitude of the input signal - it will happen gain Signal.

If you increase the bias voltage of the Base - Emitter further, it will lead to an increase in current in this chain, and as a result - an even greater current increase in the emitter - collector. At the end, the ends of the current ceases to grow - the transistor goes into a fully open state (saturation). If you then remove the offset voltage - the transistor closes, the current of the emitter - the collector will decrease, almost disappears. So the transistor can work as electronic key. This mode is most effective in terms of power management, when current flow through a fully open transistor, the value of the voltage drop is minimal. Accordingly, the current losses and the heating of transistor transitions.

There are three types of connecting bipolar transistor. With a common emitter (OE) - a strengthening of both current and voltage is carried out - the most frequently used scheme.
The amplifying cascades are constructed in a similar way, they are easier consistent with each other, since the values \u200b\u200bof their input and output resistance are relatively close, if compared with two other types of inclusion (although sometimes they differ ten times).

With a common collector (OK), the current is carried out only by current - it is used to match the sources of the signal with high internal resistance (impedance) and low-voltage load resistance. For example, at output cascades of amplifiers and controllers.

With a common base (OB), a strengthening is carried out by voltage. It has a low inlet and high output resistance and a wider frequency range. This allows you to use this inclusion to negotiate the sources of the signal with low internal resistance (impedance) followed by a stroke cascade. For example, in the input circuits of radio receivers.

Principle of operation of the field transistor.

Field transistor, as bipolar has three electrodes. They are called - stock, source and shutter. If there is no voltage on the shutter, and the positive voltage is replaced on the stock, then the maximum current flows through the source and drain through the channel.

That is, the transistor is fully open. In order to change it, a negative voltage is applied to the shutter relative to the source. Under the action of the electric field (hence the name of the transistor), the channel is narrowed, its resistance grows, and the current is reduced through it. With a certain value of the voltage, the channel is narrowed to such an extent that the current practically disappears - the transistor is closed.

The figure shows the device of a field transistor with an insulated shutter (TIR).

If a positive voltage is not submitted to the shutter of this device, the channel between the source and the runa is missing and the current is zero. The transistor is completely closed. The channel occurs at some minimum voltage on the gate (threshold voltage). Then the resistance of the channel decreases, until the transistor is completely opening.

Field transistors, both with the P-N transition (channel) and MOP (TIR), have the following inclusion schemes: with a total source (OI) - an analogue of a bipolar transistor; with a common drain (OS) - analogue OK bipolar transistor; With a common gate (OZ) - analogue about bipolar transistor.

In terms of heat dissipation, power differences:
low-power transistors - up to 100 MW;
Medium power transistors - from 0.1 to 1 W;
Powerful transistors are greater than 1 W.

Important parameters of bipolar transistors.

1. Current transmission coefficient (amplification coefficient) - from 1 to 1000 at a constant current. With increasing frequency, gradually decreases.
2. The maximum voltage between the collector and the emitter (with an open base) in special high-voltage transistors, reaches tens of thousands of volts.
3. The rate to which the current transmission coefficient is higher than 1. up to 100,000 Hz. Low-frequency transistors, over 100,000 Hz. - At high frequency.
4. The saturation of the emitter collector saturation is the value of the voltage drop between these electrodes in a fully open transistor.

Important parameters of field transistors.

The enhanced properties of the field transistor are determined by the ratio of the increment of the flow of the flow of the voltage to cause it to increments the shutter - the source, i.e.

ΔI D / ΔU GS

This relationship is made to call a steep appliance, and in fact it is a transfer conduction and is measured in milliamperes to Volt (Ma / B).

Other major parameters of field transistors are shown below:
1. I Dmax is the maximum flow current.

2.U DSMAX is the maximum stress of stock source.

3.U GSMAX is the maximum strain voltage.

4.R Dmax is the maximum power that can be allocated on the instrument.

5.T ON - a typical time increase of a flow current at the perfectly rectangular form of the input signal.

6.t OFF - Typical Time Dock Dock of the Talk at the perfect rectangular form of the input signal.

7.R DS (ON) MAX - the maximum value of the source resistance is the stock in the (open state).

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How does the transistor work?

Wide a good rice. 93. On the left in this figure you see the simplified boom of the amplifier on the transistor of the P-N-P structure and illustrations explaining the essence of this amplifier. Here, as in the previous figures, the holes of the p-type regions are conditionally depicted with circles, and the electrons of the N-type region are black balls of the same size. Remember the names of P-N transitions: between the collector and the base - the collector, between the emitter and the base - emitter.

Fig. 93. Simplified amplifier circuit on the transistor P-N-P structure and graphics illustrating its operation.

Between the collector and the emitter included the battery B K (collector), creating a negative voltage of the order of several volts at the collector relative to the issuer. In the same circuit, called the collector, is included with the load R n, which can be a telephone or a different device - depending on the assignment of the amplifier.

If the base is not connected with anything, a very weak current will appear in the collector chain (the tenths of the milliosper), since with such a polarity of the battery b to the resistance of the collector P-n of the transition will be very large; For the collector transition it will be a reverse current. The collector circuit current I increases sharply, if it is used between the base and emitter to include the bias element B C, submitting a small one to the base with a small, at least a tenth voltage, negative voltage to the emitter. That's what happens. With such an inclusion of the element B C (meaning that clamps for connecting the source of the enhanced signal marked on the circuit "~" - sinusoid, are connected by knock) in this new chain, called the base chain, will some direct current of i b; As in the diode, holes in the emitter and electrons in the database will move and neutralize, determine the current through the emitter transition.

But the fate of most of the holes entered from the emitter to the base, other than disappear when meeting with electrons. The fact is that in the manufacture of the transistors of the P-N-P structure, the saturation of holes in the emitter (and collector) is always greater than the saturation of electrons in the database. Due to this, only a small part of the holes (less than 10%), having met electrons, disappears. The main mass of holes is fluent in the base, falls under a higher negative voltage at the collector, enters the collector and in the total stream with its holes moves to its negative contact. Here, they are neutralized by the counter electrons introduced into the collector negative pole battery B. As a result, the resistance of the entire collector chain decreases and the current flows in it, many times higher than the reverse current of the collector transition. The more negative voltage based on the base, the more holes are introduced from the emitter to the database, the more significant the collector circuit current. And, on the contrary, the smaller the negative voltage based on the base, the smaller the current collector circuit of the transistor.

And if the base circuit is sequentially with a source of constant voltage that feeds this chain, enter an alternating electrical signal? The transistor will strengthen it.

The gain process in general terms is as follows. In the absence of signal voltage in the circuits of the base and the collector, there are currents of a certain amount (section O and on the charts in Fig. 93), determined by the batteries and the properties of the transistor. As soon as the signal circuit appears, respectively, the currents in the transistor circuits are also beginning to change: during negative half-periods, when the total negative voltage on the basis increases, the circuit currents increase, and during positive half-periods when the voltage of the signal and the element B with the opposite and Therefore, the negative voltage on the base is reduced, currents in both chains are also reduced. There is a strengthening of voltage and current.

If in the input circuit, i.e., a circuit of the base, the electrical signal of the sound frequency is served, and the output load - the collector - chain will be the phone, it converts the reinforced signal into the sound. If the load is the resistor, then the voltage created on it of the component of the enhanced signal can be submitted to the second transistor input circuit for additional amplification. One transistor can enhance a signal of 30 to 50 times.

The transistors of the N-P-N structure are also working, only in them the main current carriers are not holes, but electrons. In this regard, the polarity of the inclusion of elements and batteries that feed the circuit of the base and collectors of N-P-N transistors should not be such as in P-N-P transistors, but inverse.

Remembers of a very important circumstance: to the transistor base (relative to the emitter), together with the voltage of the enhanced signal, a constant voltage must be supplied, called the bias voltage, which opens the transistor.

In the amplifier according to the scheme in Fig. 93 The role of the offset voltage source performs the element b c. For the Germany transistor, the P-N-P structure should be negative and be 0.1-0.2 V, and for the transistor structure N-P-N is positive. For silicon transistors, the offset voltage is 0.5-0.7 V. Without the initial bias voltage, the emitter P-N transition "will cut", like a diode, positive (P-N-P transistor) or a negative (N-P-N transistor) of the signal, which will be accompanied by distortion. The bias voltage to the database is not served only in cases where the emitter transition transistor is used to detect the high-frequency modulated signal.

Does the bias or battery need a special element or battery for feeding to the initial bias database? Of course not. For this purpose, a collector battery voltage is usually used, connecting the database with this power source through the resistor. The resistance of such a resistor is selected by an experimental way, as it depends on the properties of this transistor.

At the beginning of this part of the conversation, I said that the bipolar transistor can be imagined as two ones on the oncoming plane diode combined in one semiconductor plate and having one common cathode, the role of which performs the base of the transistor. It is easy to make sure that you need any exemplary, but not spoiled Germany low-frequency transistor of the P-N-P structure, for example, MP39 or the similar transistors of MP40 - MP42. Between the collector and the base of the transistor, turn on the connected battery 3336l and the light bulb from the pocket lamp, calculated on the voltage of 2.5 V and the current 0.075 or 0.15 A. if the battery will be connected (via a light bulb) with a collector, and minus - with the base ( Fig. 94, a), the light bulb will burn. With a different polarity of the power on the battery (Fig. 94, b), the light bulb should not be lit.

Fig. 94. Experiments with the transistor.

How to explain these phenomena? First on the collector P-n, the transition you submitted directly, i.e. throughput voltage. In this case, the collector transition is open, its resistance is little and through it the direct current of the collector I k. The value of this current in this case is determined mainly by the bulb thread resistance and the internal resistance of the battery. With the second inclusion of the battery, its voltage was fed to the collector transition in the opposite direction. In this case, the transition is closed, its resistance is great and only a small reverse current of the collector flows through it. In a serviceable low-power low-frequency transistor, the reverse current of the collector I CBO does not exceed 30 μA. Such a current, naturally, could not heal the filament of the bulbs, so she did not burn.

Provide similar experience with the emitter transition. The result will be the same: with reverse voltage, the transition will be closed - the light bulb does not burn, and at the direct voltage it will be open - the light is on.

The following experience illustrating one of the operation modes of the transistor, according to the diagram shown in Fig. 95, a. Between the emitter and the collector of the same transistor, turn on the connected battery 3336 l and incandescent bulb. The positive pole of the battery must be connected to the emitter, and the negative - with the collector (through the filament of the light bulb). Light bulb? No, it does not burn. Connect the wire jumper base with the emitter, as shown in the barcode diagram. The light bulb included in the collector chain of the transistor will also not burn. Remove the jumper and instead of it to connect to these electrodes a series connected resistor 200 - 300 ohms and one galvanic element e b, for example, type 332, but so that the minus element is based on, and plus on the emitter. Now the light should burn. Change the polarity of the connection of the element to these electrodes of the transistor. In this case, the light bulb will not burn. Repeat several times this experience and you will make sure that the light bulb in the collector chain will be lit only when the negative voltage is valid on the basis of the transistor relative to the emitter.

Fig. 95. Experts illustrating the operation of the transistor in switching mode (A) and in amplification mode (b).

We'll figure it out in these experiments. In the first of them, when you connecting the jumper base with the emitter, the emitter transition was blocked, the transistor was simply a diode to which the inverse closing transistor was supplied. Through the transistor, only a minor reverse current of the collector transition, which could not rolling the filament of the light bulb. At this time, the transistor was in a closed state. Then, removing the jumper, you restored the emitter transition. The first inclusion of the element between the base and the emitter you submitted to the Emitter transition direct voltage. The emitter transition opened, a direct current went through it, which opened the second transistor transition - collector. The transistor turned out to be open and on the Emitter chain - the base - the collector went the transistor current, which many times the current of the Emitter chain is the base. He glue the filament of the bulbs. When you changed the polarity of the inclusion of the element to the reverse, then its voltage closed the emitter transition, and at the same time the collector transition closed. At the same time, the transistor current almost stopped (only the reverse current of the collector) and the light bulb was not burning.

In these experiments, the transistor was in one of two states: open or closed. Switching the transistor from one state to another occurred under the action of voltage based on the UB. This mode of operation of the transistor illustrated with graphs in Fig. 95, but, is called switching mode or, which is the same, key mode. Such mode of operation of the transistors is used mainly in e-automatic equipment.

What is the role of a resistor R B in these experiments? In principle, this resistor may not be. I recommended to include it solely in order to limit the current in the base chain. Otherwise, through the emitter transition will go too much direct current, as a result of which the heat breakdown can occur and the transistor fails.

If, when conducting these experiments, measuring instruments were included in the basic and collector circuit, then with closed transistor currents in its circuits almost there would be almost no. With the same transistor, the base of the base I would be no more than 2 to 3 mA, and the collector current of the I K was 60 to 75 mA. This means that the transistor can be a current amplifier.

In receiver and sound frequency amplifiers, the transistors operate in amplification mode. This mode differs from the switching mode in that using small currents in the base chain, we can control significantly large currents in the collector chain of the transistor.

Illustrate the operation of the transistor in the amplification mode, you can such experience (Fig. 95, b). In the collector chain of the transistor T included the electromagnetic telephone TF 2 between the base and minus of the power source B - resistor R B resistance 200 - 250 com. The second telephone TF 1 is included between the base and emitter through a condenser with a bond with a circuit 0.1 - 0.5 μF. You will have the simplest amplifier that can perform, for example, the role of a one-sided telephone. If your buddy will quietly talk in front of the phone included on the amplifier input, you will hear his conversation in the phones on the output of the amplifier.

What is the role of a resistor R b in this amplifier? Through it, a small initial displacement voltage, which opens the transistor and thereby ensuring it in the gain mode, is supplied to the transistor base. At the amplifier input instead of the phone TF 1, you can enable the pickup and lose the record staple. Then the sounds of the melody or voice of the singer, recorded on the gramplastine, will be well audible in the TF2 phones.

In this experience, an alternating voltage of sound frequency was served on the amplifier input, the source of which was a telephone transforming, as a microphone, sound oscillations into an electric, or a pickup, converting mechanical oscillations of its needle to electrical oscillations. This tension created in the Emitter circuit - the base is a weak alternating current, controlling a much higher current in the collector chain: with negative semi-limits on the basis of the collector current increased, and with positive - decreased (see graphics in Fig. 95, b). The signal gain occurred, and the signal enhanced by the transistor was converted by the phone included in the collector chain, into sound oscillations. The transistor worked in amplification mode.

Similar experiments can be carried out with the transistor of the N-P-N structure, for example, MP35 type. In this case, it is necessary only to change the polarity of the power supply of the transistor: the emitter must be connected with a minus, and with a collector (via the phone) - plus batteries.

Briefly about the electrical parameters of bipolar transistors. The quality and enhanced properties of bipolar transistors are estimated by several parameters that are measured using special devices. You, from a practical point of view, first of all should be interested in three basic parameters: reverse current collector I CBO Static current transmission coefficient H 21E (read like this: Ash two one e) and the boundary frequency of the current transmission coefficient gr.

Reverse current collector I CBBO is an unmanaged current through a collector P-N transition generated by non-core transistor current carriers. The parameter I CBO characterizes the quality of the transistor: than it is less, the higher the quality of the transistor. In low-power low-frequency transistors, for example, MP39 - MP42 types, I CBO should not exceed 30 μA, and at low-power high-frequency transistors - no more than 5 μA. Transistors with large values \u200b\u200bof I CBO in the work is unstable.

Static transmission coefficient H 21E characterizes the reinforcement properties of the transistor. It is called it because this parameter is measured at unchanged stresses on its electrodes and unchanged currents in its circuits. The big (title) letter "E" indicates that when measuring the transistor is included according to a circuit with a common emitter (I will tell you about the inclusion schemes in the next conversation). The coefficient H 21E is characterized by the ratio of the direct current of the collector to the direct current of the base at a constant reverse voltage of the collector - the emitter and the emitter current. The larger the numerical value of the coefficient H 21E, the greater the signal gain can provide this transistor.

The boundary frequency of the current transmission coefficient gr, expressed in kiloherts or megahertz, allows you to judge the possibility of using the transistor to enhance the oscillations of certain frequencies. The boundary frequency of transistors MP39, for example, 500 kHz, and transistors P401 - P403 - more than 30 MHz. Practically transistors are used to enhance frequencies significantly less boundary, since with an increase in frequency, the transmission current coefficient H 21E transistor decreases.

In practical work, it is necessary to take into account such parameters as the maximum allowable voltage collector - the emitter, the maximum allowable collector current, as well as the maximum allowable dispersible power collector power - the power that turns inside the transistor to heat.

Basic information about low-power transistors of mass application You will find in the application. four.

The initial name of radio components is triode, by number of contacts. This radio element is able to control the current in the electrical circuit, under the influence of the external signal. Unique properties are used in amplifiers, generators and other similar circuit solutions.

The designation of transistors in the diagram

For a long time, lamp triodics reigned in electronics. Inside the hermetic flask, three main components of the triode were placed in a special gas or vacuum environment:

• Cathode
• Grid

When a small power control signal was served on the grid, between the cathode and the anode it was possible to skip incomparable greater values. The value of the operating current of the trio is multiple times higher than the manager. This property allows the radio element to perform the role of an amplifier.

TRATIES based on radiolmps work quite effectively, especially at high power. However, dimensions do not allow them to apply them in modern compact devices.

Imagine a mobile phone or pocket player, made on such elements.

The second problem is to establish food. For normal functioning, the cathode must be strongly warmed up to the emission of electrons. Heating spiral requires a lot of electricity. Therefore, scientists of the whole world have always sought to create a more compact device with the same properties.

The first samples appeared in 1928, and in the middle of the last century, a working semiconductor triode was presented, made according to bipolar technology. The name "Transistor" was gained behind him.

What is a transistor?

The transistor is a semiconductor electrical appliance in or without or without it, having three contacts for operation and control. The main property is the same as in the trio - change the current parameters between the working electrodes using the control signal.

Due to the absence of the need for heating, transistors spend a meager amount of energy to ensure their own working capacity. And the compact dimensions of the working semiconductor crystal allow you to use radio component in small-sized structures.

Due to independence from the working medium, the semiconductor crystals can be used both in a separate housing and in chiphips. Included with other radio elements, transistors are grown directly on the single crystal.

The outstanding mechanical properties of the semiconductor found use in mobile and portable devices. Transistors are insensitive to vibration, sharp impacts. Have a good temperature resistance (cooling radiators are used with a strong load).

The necessary explanations are given, go to the point.

Transistors. Definition and History

Transistor - Electronic semiconductor device in which the current in the circuit of two electrodes is controlled by a third electrode. (Tranzistors.ru)

Field transistors (1928) were invented, and bipolar appeared in 1947 in the Bell Labs laboratory. And it was, without exaggeration, a revolution in electronics.

Very rapidly transistors replaced vacuum lamps in various electronic devices. In this regard, the reliability of such devices has increased and their dimensions have been much decreased. To this day, as far as the "Fucking" was not a microcircuit, it still contains many transistors (as well as diodes, capacitors, resistors, and so on.). Only very small.

By the way, in initially "transistors" called resistors, the resistance of which could be changed using the value of the supplied voltage. If you distract from the physics of processes, then the modern transistor can also be represented as a resistance depending on the signal submitted to it.

What is the difference between field and bipolar transistors? The answer is laid in their names themselves. In a bipolar transistor in charge transfer participate and electrons and holes ("bis" - twice). And in the field (he is unipolar) - or electrons or holes.

Also, these types of transistors differ by applications. Bipolar are used mainly in analog technology, and field-in-digital.

And, finally: the main area of \u200b\u200bapplication of any transistors - Strengthening the weak signal due to an additional power source.

Bipolar transistor. Principle of operation. Main characteristics

The bipolar transistor consists of three areas: emitter, base and collector, for each of which is supplied voltage. Depending on the type of conductivity of these areas, N-P-N and P-N-P transistors are isolated. Usually the collector area is wider than the emitter. The base is made from a slab-hazed semiconductor (because of which it has a lot of resistance) and make it very thin. Since the contact area of \u200b\u200bthe emitter base is much less than the contact area of \u200b\u200bthe base-collector, it is impossible to change the emitter and collector with the help of the connection polarity change. Thus, the transistor refers to asymmetric devices.

Before considering the physics of the transistor, outlines the overall task.


It is as follows: a strong current flows between the emitter and collector ( current current), and between the emitter and the base - a weak control current ( talk base). The collector current will change depending on the change in the base current. Why?
Consider the P-N transition transitions. There are two of them: emitter base (EB) and base collector (BC). In the active mode of the transistor, the first of them is connected to direct, and the second - with reverse displacements. What happens on the P-N transitions? For greater definiteness, we will consider the N-P-N transistor. For P-N-P, everything is similar, only the word "electrons" must be replaced by "holes".

Since the transition of the EB is open, the electrons are easily "moved" to the database. There they partially recombine with holes, but b abouttheir part of them because of the low thickness of the base and its weak doping, it time to reach the base collector. Which, as we remember, is included with the opposite. And since in the database, electrons are non-core charge carriers, the electrical field of the transition helps them overcome it. Thus, the colletur current is obtained only slightly less than the current of the emitter. And now watch your hands. If you increase the database current, the eB transition will open more, and there can be more electrons between the emitter and the collector. And since the collector current initially larger the base current, then this change will be quite and very noticeable. In this way, there will be an amplification of a weak signal arriving at the base. Once again: a strong change in the collector current is a proportional reflection of a weak database current change.

I remember my odnogroup, the principle of operation of the bipolar transistor was explained by the example of a water tap. The water in it is a collector current, and the control current of the base is how we turn the handle. A sufficiently small effort (control exposure) so that the flow of water from the crane has increased.

In addition to the processes considered, a number of phenomena may occur on the P-N transition transistor. For example, with a strong increase in the voltage at the transition, the base collector can begin avalanche reproduction of the charge due to shock ionization. And together with the tunnel effect, it will first give an electric, and then (with an increase in current) and a thermal sample. However, the thermal breakdown in the transistor may occur without electrical (i.e., without increasing the collector voltage to the punching). To do this, one excessive current will be enough through the collector.

One more phenomena is due to the fact that when changing stresses on the collector and emitter transitions, their thickness changes. And if the base is thin, then the effect of a closure may occur (the so-called "puncture" of the base) is the connection of the collector transition to the emitter. At the same time, the base area disappears, and the transistor ceases to work normally.

The collector current of the transistor in the normal active mode of operation of the transistor is larger than the current of the base as a certain number of times. This number is called current gain coefficient And is one of the main parameters of the transistor. It is denoted h21. If the transistor turns on without a load on the collector, then with a constant voltage, the emitter collector collector ratio to the current of the base will give static current gain coefficient. It can be equal to dozens or hundreds of units, but it is worth considering the fact that in real schemes this coefficient is less due to the fact that the reservoir current is turned on naturally decreases.

The second important parameter is input resistance of the transistor. According to the Ohm law, it is the voltage ratio between the base and the emitter to the base current of the base. What it is more, the smaller the current of the base and the higher the gain coefficient.

The third parameter of the bipolar transistor - voltage gain coefficient. It is equal to the ratio of amplitude or valid output values \u200b\u200b(emitter collector) and the input (base-emitter) voltage variable. Since the first value is usually very large (units and dozens of volts), and the second is very small (the tenths of the volt), then this coefficient can reach tens of thousands of units. It is worth noting that each base control signal has its own voltage gain.

Also transistors have frequency characteristicwhich characterizes the transistor's ability to enhance the signal whose frequency is approaching the grade boundary frequency. The fact is that with increasing the frequency of the input signal, the gain is reduced. This is due to the fact that the time of the core physical processes (the movement time of media from the emitter to the collector, the charge and discharge of barrier capacitive transitions) becomes commensurate with the period of change in the input signal. Those. The transistor simply does not have time to respond to changes in the input signal and at some point simply stops it to strengthen it. The frequency on which it happens and is called boundary.

Also, the parameters of the bipolar transistor are:

• reverse current collector emitter
• time inclusion
• reverse Talk of Collector
• maximum allowable current

The conventions of N-P-N and P-N-P of transistors differ only on the direction of the arrow indicating the emitter. It shows how the current flows in this transistor.

Bipolar transistor operation modes

The option discussed above is the normal active mode of operation of the transistor. However, there are several more combinations of openness / closedness of P-N transitions, each of which represents a separate operation of the transistor.

1. Inverse active mode. The transition of the BC is open here, and the eb is closed on the contrary. Enhanced properties in this mode, of course, there is no place worse, so transistors in this mode are used very rarely.
2. Saturation mode. Both transitions are open. Accordingly, the main chargers of the charge collector and the emitter "run" into the base where they are actively recombined with its main carriers. Due to the redundancy of charge carriers, the resistance of the base and P-N transitions decreases. Therefore, the circuit containing the transistor in saturation mode can be considered short-circuit, and this radio element itself is to represent as an equipotential point.
3. Cutoff mode. Both transistor transitions are closed, i.e. The current of the main charge carriers between the emitter and the collector stops. The streams of non-core charge carriers create only small and uncontrollable thermal currents of transitions. Because of the poverty of the base and transitions by carriers of charges, their resistance increases greatly. Therefore, it is often believed that the transistor operating in the cut-off mode is a rupture of the chain.
4. Barrier mode In this mode, the base is directly or through low resistance closed with a collector. Also in the collector or emitter chain include a resistor that sets current through the transistor. Thus, the equivalent of the diagram of the diode with the resistance is connected. This mode is very useful, as it allows the scheme to work almost at any frequency, in a large temperature range and is undemanding to transistor parameters.

Inclusion schemes of bipolar transistors

Since the contacts of the transistor are three, then in general, the power to it needs to be supplied from two sources, which together have four outputs. Therefore, one of the contacts of the transistor has to supply the voltage of the same sign from both sources. And, depending on what kind of contact is, there are three schemes for the inclusion of bipolar transistors: with a common emitter (OE), a common collector (OK) and a common base (OB). Each of them has both advantages and disadvantages. The choice between them is done depending on which parameters are important for us, and what you can come.

Inclusion scheme with shared emitter

This scheme gives the greatest increase in voltage and current (and from here and in power - up to tens of thousands of units), and therefore is the most common. Here the transition of the emitter base is turned on directly, and the base collector transition is back. And since the base, and the collector is given a voltage of one sign, the scheme can be powered by one source. In this scheme, the phase of the output voltage variables changes relative to the phase of the input alternating voltage by 180 degrees.

But to all buns, the scheme with OE has a significant drawback. It lies in the fact that the growth of frequency and temperature leads to a significant deterioration in the reinforcing properties of the transistor. Thus, if the transistor should work at high frequencies, it is better to use another inclusion scheme. For example, with a common database.

Inclusion scheme with a common database

This scheme does not significantly enhance the signal, but is good at high frequencies, since it allows you to more fully use the frequency response of the transistor. If the same transistor is included first according to a circuit with a common emitter, and then with a common base, then in the second case there will be a significant increase in its bone gain frequency. Since with such a connection, the input resistance is low, and the output is not very large, then the transistors collected according to the Cascade are used in the antenna amplifiers, where the wave resistance of the cables usually does not exceed 100 ohms.

In a circuit with a common database, the signal phase does not occur, and the noise level at high frequencies is reduced. But, as already mentioned, the current gain coefficient is always slightly smaller than one. True, the voltage gain coefficient here is the same as in the scheme with a common emitter. The disadvantages of the circuit with a common database can also be related to the use of two power sources.

Inclusion scheme with shared collector

The feature of this scheme is that the input voltage is completely transmitted back to the input, i.e., negative feedback is very strong.

Let me remind you that negative is called such a feedback, in which the output signal is supplied back to the input, which reduces the input level. Thus, an automatic adjustment occurs when accidental changes in the input parameters

The current gain is almost the same as in the circuit with a common emitter. But the gain coefficient is small (the main disadvantage of this scheme). It approaches one, but always less. Thus, the gain in power is obtained equal to just a few dozen units.

In the circuit with a common collector, the phase shift between the input and output voltage is missing. Since the voltage gain coefficient is close to one, the output voltage in phase and amplitude coincides with the input, i.e. repeats it. That is why such a scheme is called an emitter repeater. Emittern - because the output voltage is removed from the emitter relative to the common wire.

Such an inclusion is used to match transistor cascades or when the input source has a high input resistance (for example, a piezoelectric pickup or condenser microphone).

Two words about cascades

It happens that it is necessary to increase the output power (i.e., increase the collector current). In this case, the parallel inclusion of the required number of transistors is used.

Naturally, they must be approximately the same in characteristics. But it must be remembered that the maximum total collector current should not exceed 1.6-1.7 from the collector's limit current of any of the cascade transistors.
However (thanks to Wrewolf for the remark), in the case of bipolar transistors, it is not recommended to do so. Because the two transistors even one called at least a bit, but differ from each other. Accordingly, with parallel inclusion, the currents of different values \u200b\u200bwill flow through them. To align these currents in the emitter chains of transistors put balance resistors. The amount of their resistance is calculated so that the voltage drop on them in the operating current range was not less than 0.7 V. It is clear that this leads to a significant deterioration in the CPD of the scheme.

It may also be necessary in a transistor with good sensitivity and at the same time with a good gain coefficient. In such cases, a cascade of a sensitive, but low-power transistor (in Figure is VT1), which manages the power of a more powerful fellow (in Figure - VT2).

Other applications of bipolar transistors

Transistors can be applied not only signal amplification schemes. For example, due to the fact that they can work in saturation and cut-off modes, they are used as electronic keys. It is also possible to use transistors in signal generator circuits. If they work in key mode, the rectangular signal will be generated, and if in the amplification mode, the signal of an arbitrary shape depending on the control exposure.

Marking

Since the article has already broken up to an indecently large volume, then at this point I will simply give two good links for which the main marking systems of semiconductor devices are painted in detail (including transistors): http://kazus.ru/guide/transistors/mark_all .html and file.xls (35 KB).

Useful comments:
http://habrahabr.ru/blogs/easyelectronics/133136/#comment_4419173.

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So working diode

This is such a tricky figovin, transmitting a current only one way. It can be compared with the nipple. It is used, for example, in rectifiers, when the alternating current is constant. Or when it is necessary to separate the reverse voltage from the direct. Look at the programmer scheme (where there was an example with a divider). You see diodes stand, as you think, why? And everything is simple. In a microcontroller, logical levels are 0 and 5 volts, and Som port is a minus 12 volts, and zero plus 12 volts. Here is a diode and cuts this minus 12, forming 0 volts. And since the diode in the direct direction the conductivity is not perfect (it generally depends on the applied direct voltage than it is more, the better the diode conducts the current), then approximately 0.5-0.7 volts will fall at its resistance, the residue, being divorious resistors, will be approximately 5.5 volts, which does not go beyond the limits of the controller.
The conclusions of the diode are called the anode and cathode. Current flows from the anode to the cathode. Remember where what conclusion is very simple: on the conditional designation the arrogant and a stick from the side toatoda as if painting the letter TO look - TO| -. K \u003d cathode! And the cathode details are indicated by a strip or point.

There is another interesting type of diode - stabilirton. His I use in one of the past articles. Its feature is that in the forward direction it works as an ordinary diode, but in the opposite it breaks on any voltage, for example, by 3.3 volts. Like the restrictive valve of the steam boiler, which opens when the pressure is exceeded and the steam streaming. Stabilians use when they want to obtain the voltage of a given value, regardless of the input voltages. This may be, for example, a reference value relative to which there is a comparison of the input signal. They can trim the incoming signal to the desired value or use it as protection. In my schemes, I often put a stabilion on the nutrition of the controller to 5.5 volts, so that in the case of which if the voltage will sharply jump, this stabilion was stated through himself excess. There is also such a beast as a suppressor. The same stabilion, only much more powerful and often bidirectional. Used to protect power.

Transistor.

A terrible thing, in childhood everything could not understand how he works, but it turned out to be simple.
In general, the transistor can be compared with a controlled valve, where we control the most gluable stream. Slightly turned the handle and the tons of shit were smelled along the pipes, opened the rather and now everything around choking in unclean. Those. The output is proportional to the input multiplied to some value. This magnitude is amplification coefficient.
These devices are divided into field and bipolar.
In bipolar transistor there emitter, collector and base (see the conditional design). Emitter he with the arrow, the base is indicated as a direct area between the emitter and the collector. Between the emitter and the collector, there is a high current of payload, the current direction is determined by the arrow on the emitter. But between the base and emitter there is a small control current. Roughly speaking, the magnitude of the control current affects the resistance between the collector and the emitter. Bipolar transistors are two types: p-N-P and n-P-N The principal difference is only in the direction of the current through them.

The field transistor differs from bipolar because it resistance to the channel between the source and the drain is no longer determined by the current, but the voltage on the gate. Recently, field transistors have received huge popularity (all microprocessors are built on them), because The currents in them proceed microscopic, the crucial role plays the tension, which means that the loss and heat dissipation are minimal.

In short, the transistor will allow you a weak signal, for example, from the foot of the microcontroller ,. If there is not enough strengthening of one transistor, they can be connected by cascades - one by one, all powerful and powerful. And sometimes enough and one mighty field MOSFET. transistor. Look, for example, as in the diagrams of cell phones, the vibrating alert is controlled. There, the exit from the processor goes to the valve of power MOSFET. key