I suggest you, my dear novice electronics engineer, read this article, in which I described, perhaps, the most basic of the existing electronic components - the transistor.

A bit of history:

The invention of the transistor in the twentieth century is rightfully one of the significant events, the transistor as an electronic component has replaced vacuum tubes.Vacuum tubes for that period of time served undividedly in all radio-electronic devices, while vacuum tubes had many shortcomings. One of the most significant drawbacks was their high power consumption, as well - the lamps had a very large weight and dimensions, but at the same time they did not differ in mechanical strength. Electronic equipment became more and more complex, a large number of vacuum tubes required more energy consumption, the number of equipment failures increased - for example, computers (computers of that time) assembled on lamps could only work for a few minutes without breakdowns, and the dimensions of these “computers” were as follows, that occupied an entire high-rise building.

The semiconductor transistor is devoid of all those shortcomings that are inherent in vacuum tubes and in many ways surpasses them. Low power consumption, low weight and size, and mechanical strength is such that if you drop a modern transistor from a height of the 10th floor, nothing will happen to it.

The first transistor was developed by scientists - physicists W. Shockley, D. Bardeen and W. Brighten, in 1956 they were awarded the Nobel Prize. Now these names are known all over the world.

And so, let's take a closer look at this wonderful electronic component.

bipolar transistor

Bipolar transistor device.

A transistor is an electronic device whose body is made of metal or plastic. The case contains a silicon crystal, which is processed in a special way. This crystal consists of three parts - a collector, an emitter, a base, electrodes are connected to them, which are removed from the transistor case.Consider the symbol of a transistor, very similar to a diode, (especially the highlighted part). In principle, a transistor, with a stretch, can be called a diode, since the transistor is also a semiconductor, but the transistor has an additional element - the “base”.

The base is located between the collector and emitter and is an obstacle to the passage of voltage. In order for the transistor to perform its duties, it is necessary to “activate” the base, after which the transistor will work as a key element, as a current or voltage amplifier.

The principle of operation of the transistor.

Usually in the specialized literature and Internet sites, the description of the operation of the transistor comes down to chewing the theory of the electron-hole transition, diffusion and other tedious theory. I think if, when I was just starting to get involved in radio electronics, they had explained the principle of operation of the transistor in this way, I would have abandoned this business and went with the boys to make self-propelled guns and scarecrows, or, in the worst case, to an aircraft modeling circle). But fortunately for me, in the radio circles of that time, people worked who knew how to teach theory in such a way that it was understandable and not stressful. I will try and explain everything in a simple and accessible way.

And so, bipolar transistors come in two types PNP transistor and NPN transistor, they are also called - “direct” and “reverse” transistor. P-N-P is a direct transistor (easy to remember, the first letter P is respectively direct), N-P-N is reverse.

The diagram shows:

Consider the operation of a transistor in a key mode.

N-P-N type transistor, (+V) voltage is applied to the transistor collector to power the incandescent bulb, the bulb will not light up because the voltage does not pass through the transistor, in this case the transistor is said to be “closed”. In order for the transistor to “open” it is also necessary to apply voltage to the base of the transistor (+ Vbase). The voltage + Vbase (green arrows) will pass through the switch K1, resistor R1, through the base to the emitter and from the emitter to the minus of the power source. The transistor will open, the +V voltage (red arrows), will pass through the bulb, the collector and base to the emitter of the transistor and from the emitter to the -V power supply, the circuit will “close” and the bulb will glow.

In this example, the transistor acts as a key, opening and closing the passage of electric current.

Now consider the operation in the key mode of a transistor of the P-N-P type.

In this case, our circuit will differ in that the negative supply voltage is supplied through the light bulb to the collector, and the plus of the source is connected to the emitter of the transistor, a negative voltage -Vb must be applied to the base. The unlocking voltage (green arrows) of the plus of the power source through the emitter through the base VT, resistor R1, the switch will go to the minus of the power source and the transistor will open. The plus of the power source (red arrows) through the emitter, the base passes to the collector and through the incandescent paw to the minus power, the light will glow.

Remember the simple truth - the reverse transistor is opened by applying a positive voltage to the base, a direct negative. Even simpler - the reverse transistor opens with a plus, a direct minus. The positive power of the reverse transistor is supplied to the collector and the minus to the emitter, for the direct one, on the contrary, the negative is on the collector, plus on the emitter. Accordingly, the current in the reverse transistor flows from the collector to the emitter in the forward transistor from the emitter to the collector.

Where can you apply the operation of a transistor in a key mode?

The main advantage of the transistor lies in the fact that by applying a very small voltage of only a few tens of volts to the base, you can switch powerful actuators, for example, you can put a relay instead of a light bulb, and it will turn on a powerful electric motor with its contacts, thereby using a low control voltage we provide human security.

One more example.

The diagram shows an N-P-N transistor in the base of which a variable resistor R1 is included, with the help of this resistor you can smoothly change the voltage value applied to the base of the transistor. By moving the slider of the resistor (output with an arrow) closer to the plus of the power source (to the top of the circuit), we will thereby increase the resistance of the resistor R1, respectively, the voltage at the base of the transistor will decrease, the transistor will close, if the slider is moved in the opposite direction, the voltage at the base will increase . Have you guessed what will happen to the light bulb? I really hope that I guessed, in vain I have already written so many letters). Yes, the light bulb will change the intensity of the glow. The higher the voltage at the base of the transistor, the brighter the bulb will glow. This scheme can be successfully applied to adjust the glow of a flashlight bulb).

Now let's deal with the operation of the transistor in amplifying mode.

The transistor can work not only as a key element, but also as an amplifier for current, voltage, or both at the same time. There are several ways to turn on a transistor - this is with a common collector, a common base, and a common emitter.The circuit with a common emitter has received the greatest use, so we will consider it.

A circuit with a transistor operating in gain mode is more complex than a key circuit, but nevertheless it is not so difficult to understand the principle of its operation.

In the key mode, the transistor is in cutoff mode (closed) or in saturation mode (open) in order for the transistor to work as an amplifier, it must be made to work in the “border” mode between cutoff and saturation. Remember, we adjusted the glow of the light bulb by changing the voltage at the base of the transistor using a variable resistance (potentiometer). When the light bulb burned to the floor, this was the “border” mode, or in other words (in smart words), we set the bias to the base of the transistor.Go ahead. Let's say you decided to hear what your fish are talking about in the aquarium :), found an underwater microphone and placed it with the fish, but the microphone gives out a very weak signal and if you connect headphones to it, you won't hear anything. So you need to amplify the signal so that it is of sufficient strength.

Amplifier circuit. In this circuit, there are much more various electronic components than in the circuit where the transistor works as a key, but if you read my previous articles in the headingelectronics for beginners, you know what it is electrolytic capacitor.

In the amplifier circuit, the resistor R1 is the most important, it sets the bias current at the base of T1 to unlock the transistor, bring it from cutoff to active mode, or in other words set the base current. The value (value of resistance) of the resistor we will use will depend on the strength of the current that flows through the circuit + Upit - R1 - base - emitter and to the minus of the power source. By setting the desired base current with resistor R1, we select the operating mode of our amplifier, in which the signal from the microphone will not exceed saturation and cutoff, but will be approximately in the middle of the active mode of the transistor.The microphone produces a signal which is an alternating current, I hope you already know that the alternating current has both positive and negative polarity, respectively, either (+) or (-) will be supplied to the base of the transistor, depending on this, the transistor will open more or vice versa close. Consequently, the voltage on the collector at the connection point of the capacitor C2 will also change and at the input of the capacitor C2 you will get a copy of the input microphone signal, only amplified many times over.

Indeed, at the input of the amplifier, we apply a very small voltage from the microphone, measured in microvolts, and on the collector of the transistor, the voltage ripple will be several volts, now you can connect headphones and hear the fish :).

Of course, this amplifier circuit should not be assembled, since it has some drawbacks, but, as an example of the operation of a transistor as an amplifier, it is very suitable. Now you know how a transistor works -

The word "transistor" is formed from two words: transfer and resistor. The first word is translated from English as "transmission", the second - "resistance". Thus, this is a special kind of resistance, which is regulated by the voltage between the base and the emitter (base current) y, and the voltage between the gate and source of field-effect transistors.

Initially, several names were proposed for this semiconductor device: a semiconductor triode, a crystalline triode, a lotathron, but as a result they settled on the name “transistor” proposed by John Pierce, an American engineer and science fiction writer, a friend of William Shockley.

To begin with, let's dive a little into history, then consider some types of transistors from the electronic components common on the market today.

William Shockley, Walter Brattain, and John Bardeen, working as a team at Bell Labs, created the first workable bipolar transistor on December 16, 1947, which was officially and publicly demonstrated by scientists on December 23 of that year. It was a point transistor.

After almost two and a half years, the first germanium junction transistor appeared, then the alloyed, electrochemical, diffusion mesa transistor, and finally, in 1958, Texas Instruments released the first silicon transistor, then, in 1959, the first planar silicon transistor was created by Jean Ernie, as a result, germanium was supplanted by silicon, and planar technology took pride of place as the main technology for the production of transistors.

In fairness, we note that in 1956, William Shockley, John Bardeen and Walter Brattain received the Nobel Prize in Physics "for their research on semiconductors and the discovery of the transistor effect."

As for field-effect transistors, the first patent applications were filed from the mid-20s of the 20th century, for example, in Germany, physicist Julius Edgar Lilienfeld patented the principle of operation of field-effect transistors in 1928. However, the field-effect transistor itself was patented for the first time in 1934 by the German physicist Oskar Heil.

The operation of a field effect transistor basically uses the electrostatic effect of the field, physically it is simpler, therefore the very idea of ​​\u200b\u200bfield effect transistors appeared earlier than the idea of ​​\u200b\u200bbipolar transistors. The first field-effect transistor was made for the first time in 1960. As a result, closer to the 90s of the 20th century, MOS technology (metal-oxide-semiconductor field-effect transistor technology) began to dominate in many industries, including the IT sphere.

In most applications, transistors have replaced vacuum tubes, a real silicon revolution has taken place in the creation of integrated circuits. So, today in analog technology bipolar transistors are more often used, and in digital technology - mainly field ones.

The device and principle of operation of field and are the topics of separate articles, so we will not dwell on these subtleties, but consider the subject from a purely practical point of view using specific examples.

As you already know, according to the manufacturing technology, transistors are divided into two types: field and bipolar. Bipolar, in turn, are divided by conductivity into n-p-n - reverse conduction transistors, and p-n-p - forward conduction transistors. Field-effect transistors are, respectively, with an n-type and p-type channel. The gate of a field effect transistor can be insulated (IGBT transistors) or in the form of a p-n junction. I come with a built-in channel or with an induced channel.

The areas of application of transistors are determined by their characteristics, and transistors can operate in two modes: in key or in amplifying. In the first case, the transistor is either fully open or fully closed during operation, which allows you to control the power supply of significant loads using a small current for control. And in amplifying, or in other words - in dynamic mode, the property of the transistor is used to change the output signal with a small change in the input, control signal. Next, consider examples of various transistors.

2N3055 - bipolar n-p-n-transistor in TO-3 package. Popular as part of the output stages of high quality audio amplifiers, where it operates in dynamic mode. As a rule, it is used in conjunction with the complementary p-n-p counterpart MJ2955. This transistor can also operate in a key mode, for example, in transformer low-frequency inverters 12 to 220 volts 50 Hz, a pair of 2n3055 controls a push-pull converter.

It is noteworthy that the collector-emitter voltage for this transistor during operation can reach 70 volts, and the current is 15 amperes. The TO-3 case allows you to conveniently mount it on the radiator if necessary. The static current transfer coefficient is from 15 to 70, which is enough to effectively control even powerful loads, despite the fact that the base of the transistor can withstand current up to 7 amperes. This transistor can operate at frequencies up to 3 MHz.

KT315 - a legend among domestic low-power bipolar transistors. This n-p-n-type transistor first saw the light in 1967, and to this day is popular in the amateur radio environment. Its complementary pair is KT361. Ideal for dynamic and key applications in low power circuits.

With a maximum allowable collector-emitter voltage of 60 volts, this high-frequency transistor is capable of passing a current of up to 100 mA through itself, and its cut-off frequency is at least 250 MHz. The current transfer ratio reaches 350, while the base current is limited to 50 mA.

Initially, the transistor was produced only in a plastic KT-13 package, 7 mm wide and 6 mm high, but recently it can also be found in the TO-92 package, for example, manufactured by Integral OJSC.

KP501 - field-effect n-channel low-power transistor with an insulated gate. It has an enriched n-channel, the resistance of which is from 10 to 15 ohms, depending on the modification (A, B, C). This transistor is intended, as the manufacturer positions it, for use in communication equipment, telephones and other electronic equipment.

This transistor can be called a signal transistor. A small TO-92 case, the maximum drain-source voltage is up to 240 volts, the maximum drain current is up to 180 mA. Gate capacitance less than 100pf. Particularly noteworthy is that the gate threshold voltage is between 1 and 3 volts, which makes it possible to implement control at very, very low cost. Ideal as a signal level converter.

irf3205 - n-channel field-effect transistor made using HEXFET technology. Popular as a power switch for high frequency boost inverters such as automotive. By connecting several cases in parallel, it is possible to build converters designed for significant currents.

The maximum current for one such transistor reaches 75A (the limitation is introduced by the design of the TO-220 case), and the maximum drain-source voltage is 55 volts. The channel resistance is only 8 mΩ. A gate capacitance of 3250 pf requires a powerful driver to drive high frequencies, but this is not a problem today.

FGA25N120ANTD Powerful Insulated Gate Bipolar Transistor (IGBT) in TO-3P Package. Able to withstand a drain-source voltage of 1200 volts, the maximum drain current is 50 amperes. The peculiarity of manufacturing modern IGBT transistors of this level allows them to be classified as high-voltage.

Scope - inverter-type power converters, such as induction heaters, welding machines and other high-frequency converters designed for high voltage power supply. Ideal for high-power bridge and half-bridge resonant converters, as well as for hard switching conditions, there is a built-in high-speed diode.

We have considered here only a few types of transistors, and this is only a tiny part of the abundance of models of electronic components on the market today.

One way or another, you can easily choose the right transistor for your purposes, fortunately, the documentation for them is available today on the net in the form of datasheets, which exhaustively present all the characteristics. The package types of modern transistors are different, and for the same model, both SMD and output versions are often available.

Andrey Povny

Electronics surrounds us everywhere. But almost no one thinks about how this whole thing works. In fact, everything is quite simple. That is what we will try to show today. And let's start with such an important element as a transistor. We will tell you what it is, what it does, and how a transistor works.

What is a transistor?

Transistor- a semiconductor device designed to control electric current.

Where are transistors used? Yes, everywhere! Almost no modern electrical circuit can do without transistors. They are widely used in the production of computer technology, audio and video equipment.

Times when Soviet microcircuits were the largest in the world, have passed, and the size of modern transistors is very small. So, the smallest of the devices have a size of the order of a nanometer!

Console nano denotes a magnitude of the order of ten to the minus ninth power.

However, there are giant specimens that are used mainly in the fields of energy and industry.

There are different types of transistors: bipolar and polar, direct and reverse conduction. However, the operation of these devices is based on the same principle. A transistor is a semiconductor device. As is known, charge carriers in a semiconductor are electrons or holes.

The region with an excess of electrons is denoted by the letter n(negative), and the region with hole conductivity p(positive).

How does a transistor work?

To make everything very clear, consider the work bipolar transistor (the most popular type).

(hereinafter referred to as simply a transistor) is a semiconductor crystal (most often used silicon or germanium), divided into three zones with different electrical conductivity. Zones are named accordingly collector, base And emitter. The transistor device and its schematic representation are shown in the figure below.

Separate transistors of direct and reverse conductivity. P-n-p transistors are called forward-conducting transistors, and n-p-n transistors are called reverse ones.

Now about what are the two modes of operation of transistors. The very operation of the transistor is similar to the operation of a water tap or valve. Only instead of water - electric current. Two states of the transistor are possible - working (transistor open) and resting state (transistor closed).

What does it mean? When the transistor is closed, no current flows through it. In the open state, when a small control current is applied to the base, the transistor opens, and a large current begins to flow through the emitter-collector.

Physical processes in a transistor

And now more about why everything happens this way, that is, why the transistor opens and closes. Let's take a bipolar transistor. Let it be n-p-n transistor.

If you connect a power supply between the collector and emitter, the collector electrons will begin to be attracted to positive, but there will be no current between the collector and emitter. This is prevented by the base layer and the emitter layer itself.

If, however, an additional source is connected between the base and the emitter, electrons from the n region of the emitter will begin to penetrate into the region of the bases. As a result, the base region will be enriched with free electrons, some of which will recombine with holes, some will flow to the plus of the base, and some (most) will go to the collector.

Thus, the transistor turns open, and the emitter-collector current flows in it. If the base voltage is increased, the collector-emitter current will also increase. Moreover, with a small change in the control voltage, a significant increase in the current through the collector-emitter is observed. It is on this effect that the operation of transistors in amplifiers is based.

That's the whole point of how transistors work in a nutshell. Do you need to design a bipolar transistor power amplifier overnight, or do some lab work to study the operation of a transistor? This is not a problem even for a beginner, if you use the help of our student service specialists.

Feel free to seek professional help with important matters like studying! And now that you already have an idea about transistors, we invite you to relax and watch the video of the Korn band “Twisted transistor”! For example, you decide, contact the Correspondence.

A transistor (transistor, English) is a triode, made of semiconductor materials, with three outputs, the main property of which is to control a significant current at the output of the circuit with a relatively low input signal. In radio components, from which modern complex electrical appliances are assembled, field-effect transistors are used. Their properties allow solving problems of turning off or turning on the current in the electrical circuit of the printed circuit board, or amplifying it.

What is a field effect transistor

A field effect transistor is a device with three or four contacts in which current on two contacts is adjustable voltage of the electric field on the third. Therefore, they are called field.

Contacts:

A field-effect transistor with an n - p junction is a special type of transistors that serve for current control.

It differs from a simple ordinary one in that the current passes through it without crossing the p-n junction zone, the zone formed on the borders of these two zones. The size of the p-n zone is adjustable.

Field effect transistors, their types

Field-effect transistors with n - p junction are divided into classes:

1. By type of conductor channel: n or p. The sign, polarity, control signal depends on the channel. It must be opposite in sign to the n-zone.
2. According to the structure of the device: diffuse, alloyed by p - n - transition, with a gate, thin-film.
3. According to the number of contacts: 3 and 4-pin. In the case of a 4-pin device, the substrate also acts as a gate.
4. According to the materials used: germanium, silicon, gallium arsenide.

Classes are divided according to the principle of work:

• device running p - n transition;
• insulated gate or Schottky barrier device.

Field effect transistor, principle of operation

In a simple way, how a field-effect transistor with a control pn junction works can be said like this: the radio component consists of two zones: p - junction and n - junction. An electric current flows through zone n. The p zone is an overlapping zone, a kind of valve. If you press hard on it, it blocks the area for the passage of current and it passes less. Or, if the pressure to reduce will pass more. Such pressure is carried out by increasing the voltage at the gate contact located in the p zone.

A device with a control p - n channel junction is a semiconductor wafer with one of these types of electrical conductivity. Contacts are connected to the ends of the plate: drain and source, in the middle - a gate contact. The operation of the device is based on the variability of the thickness of the p-n transition space. Since there are almost no mobile charge carriers in the blocking region, its conductivity is zero. In the semiconductor wafer, in the area not affected by the blocking layer, a current-conducting channel is created. When a negative voltage is applied with respect to the source, a flow is created at the gate, through which charge carriers flow.

In the case of an insulated gate, a thin dielectric layer is placed on it. This kind of device works on the principle of electric field. A small amount of electricity is enough to destroy it. Therefore, to protect against static voltage, which can reach thousands of volts, special instrument cases are created - they allow minimizing the impact of viral electricity.

Why do you need a field effect transistor

Considering the operation of complex electronic equipment, as the operation of a field-effect transistor (as one of the components of an integrated circuit), it is difficult to imagine that main directions of his work five:

1. High frequency amplifiers.
2. Low frequency amplifiers.
3. Modulation.
4. DC amplifiers.
5. Key devices (switches).

In a simple example, the operation of a transistor as a switch can be thought of as arranging a microphone with a light bulb. The microphone picks up the sound, from which an electric current appears. It goes to a locked field effect transistor. With its presence, the current turns on the device, turns on the electrical circuit to which the light bulb is connected. The lamp lights up when sound is picked up by the microphone, but it lights up due to a power source that is not connected to the microphone and is more powerful.

Modulation applied to control the information signal. The signal controls the oscillation frequency. Modulation is used for a high-quality sound signal in radio, for the transmission of a sound range in television programs, for broadcasting color and a high-quality television signal. It is applied everywhere where work with material of high quality is required.

Like an amplifier the field-effect transistor works in a simplified way: graphically, any signal, in particular, the sound series, can be represented as a broken line, where its length is time, and the height of the breaks is the frequency of sound. To amplify the sound, a powerful voltage is applied to the radio component, which acquires the necessary frequencies, but with higher values, by applying a weak signal to the control contact. In other words, the device redraws the original line proportionally, but with higher peak values.

Application of field effect transistors

The first device that went on sale, which used a field-effect transistor with a control p-n junction, was hearing aid. Its appearance was recorded in the fifties of the last century. On an industrial scale, they were used in telephone exchanges.

In today's world, devices are used in all electrical engineering. Due to the small size and variety of characteristics of the field-effect transistor, it can be found in kitchen appliances, audio and television equipment, computers and electronic children's toys. They are used in alarm systems of both security mechanisms and fire alarms.

In factories, transistor equipment is used for power controllers of machine tools. In transport, from the operation of equipment on trains and locomotives, to the fuel injection system of private cars. In housing and communal services from dispatching systems to street lighting control systems.

One of the most important applications of transistors is processor manufacturing. In fact, the entire processor consists of many miniature radio components. But when switching to an operating frequency above 1.5 GHz, they begin to consume energy like an avalanche. Therefore, processor manufacturers have chosen the path of multi-core, and not by increasing clock frequencies.

Pros and cons of field effect transistors

Field effect transistors with their characteristics left far behind other species devices. They are widely used in integrated circuits as switches.

• the cascade of parts consumes little energy;
• amplification is higher than in other species;
• high noise immunity is achieved by the absence of current flow in the gate;
• higher turn-on and turn-off speed - they can operate at frequencies inaccessible to other transistors.

• lower breakdown temperature than other species;
• at a frequency of 1.5 GHz, the energy consumed begins to increase sharply;
• sensitivity to static electricity.

The characteristics of semiconductor materials taken as the basis of field-effect transistors made it possible use devices in everyday life and production. On the basis of trifling transistors, household appliances were created in the form familiar to a modern person. Processing of high-quality signals, production of processors and other high-precision components is impossible without the achievements of modern science.

This is such a tricky thing that passes current only in one direction. It can be compared to a nipple. It is used, for example, in rectifiers, when alternating current is made direct. Or when it is necessary to separate the reverse voltage from the direct one. Look at the programmer circuit (where there was an example with a divider). You see there are diodes, what do you think, why? And everything is simple. For the microcontroller, the logic levels are 0 and 5 volts, and for the COM port, one is minus 12 volts, and zero is plus 12 volts. Here the diode cuts off this minus 12, forming 0 volts. And since the conductivity of the diode in the forward direction is not ideal (it generally depends on the applied forward voltage, the larger it is, the better the diode conducts current), then about 0.5-0.7 volts will drop on its resistance, the remainder, being divided by resistors in two, will be approximately 5.5 volts, which is within the limits of the controller.
The terminals of a diode are called an anode and a cathode. Current flows from the anode to the cathode. It is very simple to remember where which conclusion is: on the symbol, the arrow and the stick from the side To as if drawing a letter TO here look - TO|—. K = Cathode! And on the part, the cathode is indicated by a strip or a dot.

There is another interesting type of diode - zener diode. I used it in one of the previous articles. Its peculiarity is that in the forward direction it works like a conventional diode, but in the reverse direction it breaks off at some voltage, for example, at 3.3 volts. Similar to a steam boiler pressure relief valve that opens when pressure is exceeded and bleeds off excess steam. Zener diodes are used when they want to get a voltage of a given value, regardless of the input voltages. This can be, for example, a reference value against which the input signal is compared. They can cut the incoming signal to the desired value or use it as protection. In my circuits, I often put a 5.5 volt zener diode to power the controller, so that if something happens, if the voltage jumps sharply, this zener diode bleeds the excess through itself. There is also such a beast as a suppressor. The same zener diode, only much more powerful and often bidirectional. Used for nutrition protection.

Transistor.

A terrible thing, as a child I could not understand how it works, but everything turned out to be simple.
In general, a transistor can be compared to a controlled valve, where we control the most powerful flow with a tiny effort. He turned the handle a little and tons of shit rushed through the pipes, opened it harder and now everything around was choked in sewage. Those. The output is proportional to the input multiplied by some value. This value is the gain.
These devices are divided into field and bipolar.
The bipolar transistor has emitter, collector And base(see drawing of symbol). The emitter is with an arrow, the base is designated as a straight platform between the emitter and the collector. There is a large payload current between emitter and collector, the direction of the current is determined by the arrow on the emitter. But between the base and the emitter there is a small control current. Roughly speaking, the magnitude of the control current affects the resistance between the collector and emitter. Bipolar transistors are of two types: p-n-p And n-p-n the fundamental difference is only in the direction of the current through them.

A field-effect transistor differs from a bipolar one in that in it the channel resistance between the source and drain is no longer determined by the current, but by the gate voltage. Recently, field-effect transistors have gained immense popularity (all microprocessors are built on them), because. microscopic currents flow in them, voltage plays a decisive role, which means that losses and heat generation are minimal.

In short, the transistor will allow you a weak signal, for example from the foot of the microcontroller,. If the amplification of one transistor is not enough, then they can be connected in cascades - one after the other, more and more powerful. And sometimes one mighty field MOSFET transistor. Look, for example, how a vibrating alert is controlled in cell phone circuits. There, the output from the processor goes to the gate of the power MOSFET key.