What is necessary for the transistor in the electrical circuit. Basics of electronics for dummies: what is a transistor and how it works

The transistor refers to the category of semiconductor devices. In electrical engineering, it is used as a generator and an electric oscillation amplifier. The basis of the device is a crystal located in the housing. For the manufacture of the crystal, a special semiconductor material is used, in its properties located in an intermediate position between the insulator and the conductor. The transistor is used in radio and electronic circuits. These devices can be. Each of them has its own parameters and characteristics.

Features of bipolar transistors

The electric current in bipolar transistors is formed by electrical charges having a positive and negative polarity. The holes transfer positive polarity, and electrons are negative. For this type of devices, germanium or silicon crystals are used, which have individual characteristics that are taken into account when creating electronic circuits.

The basis of the crystal is ultrapure materials. Special impurities are added to them in an accurate dosage. It is they affect the emergence of an electronic or hole conduction in the crystal. They are indicated, respectively, as N- or P-conductivity. There is a base of the base, which is one of the electrodes. Special impurities introduced into the crystalline surface change the conductivity of the base to the opposite value. As a result, the N-P-N or P-N-P zones are formed to which the conclusions are connected. Thus, the creation of the transistor occurs.

The source of charge carriers is called an emitter, and the media collector is a collector. Between them there is a zone that performs the role of the base. The instrument conclusions are called in accordance with the connected electrodes. When an input signal is received in the form of a small electrical voltage, the circuit between it and the collector will flow. The form of this current coincides with the input signal, but its value increases significantly. This is precisely the enhancing properties of the transistor.

Work of field transistor

In field transistors, the directional movement of electrons or holes is formed under the influence of the electric field, which is created on the third electrode applied voltage. The carriers are out of one electrode, so it is called the source. The second electrode to which charges come, is the name of the drain. The third electrode controlling the movement of particles is called a shutter. The conductive area limited to the drain and source is called the channel, so the device data is still known as channels. The resistance of the channel varies under the action of the voltage generated on the gate. This factor has an impact on the electric current flowing through the channel.

The type of charge carriers affects the characteristics. In the N-channel, the directional movement of electrons occurs, and holes move in the R-channel. Thus, the current appears under the action of carriers only with some one sign. This is the main difference between field and bipolar transistors.

The principle of operation of each field transistor consists in unipolar current, requires constant voltage to ensure the initial displacement. The polarity value depends on the type of channel, and the voltage is associated with one or another type of device. In general, they are reliable in operation, can work in a wide frequency range, have a large input resistance.

In all experiments, CT315B transistors are used, D9B diodes, miniature incandescent bulbs by 2.5V x 0.068a. Headphones are high-resistant, type tone-2. A variable condenser - any, with a capacity of 15 ... 180 PF. The battery consists of two consistently connected 4.5V batteries 3R12. Lamps can be replaced by the consecutive connected LED of the al307a type and resistor with a par value of 1 com.

Experiment 1.
Electrical circuit (conductors, semiconductors and insulators)

Electric current is the directional movement of electrons from one pole to another under the action of voltage (9 V battery).

All electrons have the same negative charge. Atoms of various substances have a different number of electrons. Most electrons are firmly associated with atoms, but there are also so-called "free", or valence, electrons. If the ends of the conductor attach the voltage, then the free electrons will start moving to the positive pole of the battery.

In some materials, the movement of electrons is relatively free, they are called conductor; In others, moving is difficult, they are called semiconductors; In third, it is generally impossible, such materials are called insulators, or dielectrics.

Metals are good current conductors. Such substances like mica, porcelain, glass, silk, paper, cotton, belong to insulators.

Semiconductors include germanium, silicon and other conductors these substances become under certain conditions. This property is used in the production of semiconductor devices - diodes, transistors.

Fig. 1. Determination of water conductivity

This experiment demonstrates the operation of a simple electrical circuit and the difference in conductivity of conductors, semiconductors and dielectrics.

Collect the scheme as shown in Fig. 1, and output the curtain ends of the wires on the front of the board. Connect the curtain ends together, the light bulb will burn. This suggests that electric current passes through the chain.

With the help of two wires, you can check the conductivity of various materials. To accurately determine the conductivity of certain materials, special devices are needed. (On the brightness of the combustion of the bulbs, you can only determine whether the material studied is a good or bad conductor.)

Attach the curtain ends of two conductors to a dry wood piece at a short distance from each other. Light bulb will not burn. This means that dry wood is a dielectric. If the curtain ends of two conductors to attach to aluminum, copper or steel, the light bulb will burn. This suggests that metals are good electrical current conductors.

Lower the curtain ends of the conductors into a glass with tap water (Fig. 1, a). Light bulb does not burn. This means that water is a bad current conductor. If adding a little salt and repeat the experience (Fig. 1, b), the light bulb will burn, which indicates the flow of current in the chain.

The 56 ohm resistor in this scheme and in all subsequent experiments serves to limit the current in the chain.

Experiment 2.
Action diode.

The purpose of this experiment is a visual demonstration that the diode is well conducted in one direction and does not conduct - in the opposite.

Collect the scheme as shown in Fig. 2, a. The lamp will burn. Turn the diode 180 ° (Fig. 2, b). Light bulb will not burn.

And now we will try to figure out the physical essence of the experiment.

Fig. 2. The action of the semiconductor diode in the electronic chain.

Semiconductors Germanium and silicon have four free, or valence, electron. The semiconductor atoms are binding to dense crystals (crystalline grille) (Fig. 3, a).

Fig. 3. Crystal grille of semiconductors.

If in a semiconductor having four valence electrons, introduce an impurity, such as arsenic having five valence electrons (Fig. 3, b), then the fifth electron in the crystal will be free. Such impurities provide electronic conductivity, or N-type conductivity.

Impurities having less valence than semiconductor atoms have the ability to attach electrons to itself; Such impurities provide hole conductivity, or p-type conductivity (Fig. 3, B).

Fig. 4. P-N-transitions in semiconductor diode.

The semiconductor diode consists of falling out the materials of P- and N-types (P-N-transition) (Fig. 4, a). Depending on the polarity of the applied voltage, the P-N-transition can either contribute (Fig. 4, d), or to prevent (Fig. 4, c) the passage of the electric current. At the border of two semiconductors, even before the supply of external voltage, a binary electric layer was created with a local electric field of e 0 (Fig. 4, b).

If you pass alternating current through the diode, then the diode will only pass the positive half-wave (Fig. 4 g), and the negative pass will not pass (see Fig. 4, B). The diode, thus converts, or "straightens", alternating current into constant.

Experiment 3.
How the transistor works

This experiment clearly demonstrates the main function of the transistor, which is an amplifier. A small control current in the base circuit may cause a high current in the Emitter circuit - collector. By changing the resistance of the base resistor, you can change the current collector.

Collect the scheme (Fig. 5). Put in the schema alternately resistors: 1 Mom, 470 com, 100 com, 22 com, 10 com. It can be seen that with resistors of 1 MΩ and 470 kΩ, the bulb does not burn; 100 kΩ - the light bulb is barely lit; 22 kΩ - the light burns brighter; Full brightness is observed when connecting the base resistor 10 com.

Fig. 6. Transistor with N-P-N structure.

Fig. 7. Transistor with the P-N-P structure.

The transistor is essentially two semiconductor diodes having one common area - base. If the total region with p-conductivity is common, then the transistor with the N-P-N structure (Fig. 6) will be obtained; If the common area is with N-conductivity, the transistor will be with the P-N-P structure (Fig. 7).

Transistor region emitting (emigrating) current carriers is called an emitter; The area collecting current carriers is called a collector. The zone concluded between these areas is called the base. The transition between the emitter and the base is called emitter, and between the base and collector - collector.

In fig. 5 shows the inclusion of the transistor of the N-P-N transistor into the electrical circuit.

When the P-N-P transistor circuit is turned on, the polarity of the battery function B changes to the opposite.

For currents flowing through the transistor, there is a dependency

I e \u003d i b + i to

Transistors are characterized by a current gain as the letter β, represents the ratio of the recreation of the collector current to the change in the base current.

The value of β lies in the range of several dozen to several hundred units depending on the type of transistor.

Experiment 4.
Properties of condenser

Having studied the principle of the transistor, you can demonstrate the properties of the condenser. Collect the scheme (Fig. 8), but do not attach an electrolytic capacitor 100 μF. Then plug it for a while in position A (Fig. 8, a). Light bulb will light up and go out. This suggests that the charge of the charge of the capacitor was in the chain. Now place the capacitor to position in (Fig. 8, b), with the hands do not touch the conclusions, otherwise the capacitor can discharge. The light bulb will light up and go out, the discharge of the capacitor occurred. Now, again, place the capacitor in position A. There was his charge. Put the capacitor for a while (10 seconds) to the side of the insulating material, then place the lamp in position. The light lights up and goes out. From this experiment it is clear that the capacitor is able to accumulate and store an electrical charge for a long time. The accumulated charge depends on the capacitance capacitor.

Fig. 8. Scheme explaining the principle of the condenser operation.

Fig. 9. Change voltage and current on the condenser in time.

Condifted the capacitor charge by setting it to the position A, then discharge it by attaching it to the condenser condenser condenser with random ends (the conductor hold for an isolated part!), And place it in position. V. Light bulb will not light up. As can be seen from this experiment, the charged capacitor performs the role of a power source (battery) in the base chain, but after using the electric charge, the bulb goes out. In fig. 9 are dependable on time: capacitor charge voltage; Current charge flowing into the chain.

Experiment 5.
Transistor as a switch

Collect the scheme according to fig. 10, but not yet install the R1 resistor and the T1 transistor in the circuit. The key in must be connected to the diagram at the point A and E so that the point of connection of the resistors R3, R1 can be closed on the shared wire (minus printed circuit board bus).

Fig. 10. The transistor in the diagram works as a switch.

Connect the battery, the light bulb in the T2 collector chain will burn. Now close the circuit with a switch. The light bulb will go out, as the switch connects the point A with a minus tire, thereby reducing the potential of the point A, consequently, the potential of the T2 base. If the switch is returned to its original position, the light bulb will light up. Now disconnect the battery and connect T1, the R1 resistor does not connect. Connect the battery, the light bulb will turn back again. As in the first case, the T1 transistor is open and an electric current passes through it. Now put the R1 resistor (470 com) at points C and D. The light will go out. Remove the resistor, and the light bulb will light up again.

When the voltage on the T1 collector drops to zero (when installing a resistor 470 kΩ), the transistor opens. The base of the T2 transistor connects through T1 to the minus tire, and the T2 is closed. Light bulb goes out. Thus, the T1 transistor performs the role of switch.

In previous experiments, the transistor was used as an amplifier, now it is used as a switch.

The use of the transistor as a key (switch) is given in experiments 6, 7.

Experiment 6.
ALARM

A feature of this scheme is that the T1 transistor used as a key is controlled by the R2 photoresistor.

A photoresistor available in this set changes its resistance from 2 kΩ with strong illumination to several hundred comes in the dark.

Collect the scheme according to fig. 11. Depending on the lighting of the room, where you carry out the experiment, select the R1 resistor so that the light bulb is normal without dimming the photoresistor.

Fig. 11. Chart of alarm based on photoresistor.

The state of the transistor T1 is determined by the voltage divider consisting of a resistor R1 and a photoresistor R2.

If the photoresistor is lit, its resistance is not enough, the T1 transistor is closed, there is no current in its collector chain. The state of the transistor T2 is determined by the supply of the positive potential of the resistors R3 and R4 to the base T2. Consequently, the T2 transistor opens, the collector current flows, the light is on.

When the photoresistor is darkened, its resistance increases greatly and reaches the value when the divider supplies the voltage to the base T1, sufficient to open it. The voltage on the T1 collector drops almost to zero, the T2 transistor is locked through the R4 resistor, the bulb goes out.

In practice, other actuators (call, relay, etc.) can be installed in such schemes in the collector circuit of the T2 transistor T2.

In this and in subsequent schemes, a SF2-9 type photoresistor or a similar one can be used.

Experiment 7.
Automatic light power device

In contrast to the experiment 6, in the given experiment, during the darkening of the photoresistor R1, the bulb is on (Fig. 12).

Fig. 12. Scheme including light automatically.

When light enters the photoresistor, its resistance is strongly reduced, which leads to the opening of the transistor T1, and therefore, to the closure of T2. Light bulb does not burn.

In the dark, the bulb turns on automatically.

This property can be used to turn on and off lamps depending on the illumination.

Experiment 8.
Signal device

A distinctive feature of this scheme is a big sensitivity. In this and a number of subsequent experiments, the combined connection of transistors (composite transistor) is used (Fig. 13).

Fig. 13. Optoelectronic signaling device.

The principle of this scheme does not differ from the scheme. With a certain value of the resistance of resistors R1 + R2 and the resistance of the photoresistor R3 in the transistor circuit of the T1 transistor flows. In the collector circuit, the T1 also flows the current, but in (3 times a larger current of the base T1. Suppose that (β \u003d 100. The entire current going through the emitter T1 must pass through the transition of the emitter - the base T2. Then the current collector T2 in β times The current of the collector T1, the current collector T1 in β times the current of the base T1, the current collector T2 is approximately 10,000 times the current of the base T1. Thus, the composite transistor can be considered as a single transistor with a very large gain and large sensitivity. The second feature The composite transistor is that the T2 transistor must be quite powerful, while the T1 transistor controller can, be low, since the current passing through it is 100 times less than the current passing through T2.

The performance of the scheme shown in Fig. 13, determined by the illumination of the room where the experiment is carried out, so it is important to select the resistance of the R1 of the upper shoulder divider so that in the illuminated room the light bulb is not burning, and it was burning with a darkening of the photoresistor hand, the darkening of the room with curtains or when the light is turned off in the evening.

Experiment 9.
Humidity sensor

In this scheme (Fig. 14), a composite transistor with a large sensitivity is also used to determine the humidity of the material. The database displacement T1 is provided by the R1 resistor and two conductors with severe ends.

Check the electrical circuit, slightly squeezing with the fingers of both hands of the cereal ends of two conductors, while not connecting them with each other. The resistance of the fingers is enough to trigger the scheme, and the light bulb lights up.

Fig. 14. Moisture sensor scheme. Uninsulated carts of conductors permeate the blotting paper.

Now the curtain ends will pass through the wreaking paper at a distance of about 1.5-2 cm, other ends attach to the diagram according to fig. 14. Then Moisten the wrapping paper between the wires. The light bulb lights up (in this case, the decrease in resistance occurred due to the dissolution of the water in the salts available in paper.).

If sheepbearing paper is soaked with a salt solution, and then dry and repeat the experience, the effectiveness of the experiment increases, the ends of the conductors can be dissected for a greater distance.

Experiment 10.
Signal device

This scheme is similar to the previous one, the only difference is that the lamp is lit when the photoresistor is illuminated and goes out when the darkening (Fig. 15).

Fig. 15. Signal device on photoresistor.

The scheme works as follows: with the usual illumination of the photoresistor R1, the light will burn, since the resistance R1 is not enough, the T1 transistor is open. When the light is turned off the light goes out. The light of a pocket lantern or lit mat will make the light bulb burn again. The sensitivity of the chain is regulated by increasing or decreasing resistance of the resistor R2.

Experiment 11.
Counter of Products

This experiment must be carried out in a half-mounted room. All the time when the light falls on the photoresistor, the L2 indicator light burns. If you put a piece of cardboard between the light source (L1 light bulb and a photoresistor, L2 lights goes out. If you remove the cardboard, the L2 light lights up again (Fig. 16).

Fig. 16. Product Counter.

In order for the experiment to successfully, it is necessary to adjust the scheme, that is, to select the resistance of the resistor R3 (the most suitable in this case is 470 ohms).

This scheme can practically be used to count the product batch on the conveyor. If the light source and the photoresistor are placed in such a way that a batch of products passes between them, the chain is turned on, then it turns off, since the flow of light is interrupted by passing products. Instead of the L2 indicator light bulb, a special counter is used.

Experiment 12.
Signal transmission with light

Fig. 23. Frequency divider on transistors.

T1 and T2 transistors open alternately. The control signal is sent to the trigger. When the T2 transistor is open, the L1 light is not lit. Lamp light lights up when the T3 transistor is open. But the T3 and T4 transistors are open and closed alternately, therefore, the L2 light lights up at each second control signal, sending a multivibrator. Thus, the frequency of burning light bulb L2 is 2 times less than the frequency of the light bulb L1.

This property can be used in the electorgano: the frequencies of all the notes of the upper octave organs are divided in half and the temperature is created below. The process may be repeated.

Experiment 18.
Scheme "And" by units

In this experiment, the transistor is used as a key, and the light bulb is an output indicator (Fig. 24).

This scheme is logical. The light bulb will burn if there will be high potential on the basis of the transistor (point C).

Suppose, points A and B are not connected to a negative tire, they have a high potential, therefore, at a point with also high potential, the transistor is open, the light bulb is on.

Fig. 24. Logical element 2I on the transistor.

We accept conditionally: high potential - logical "1" - the light burns; Low potential is a logical "0" - the light is not lit.

Thus, if there is in points A and in logical "1", at a point with also will be "1".

Now connect a point and with a negative bus. Its potential will be low (falls to "0" c). Point in has a high potential. According to R3 - D1 chains - the battery will flow current. Consequently, at the point C will be low potential or "0". The transistor is closed, the bulb is off.

Connect from the ground the point V. The current is now flowing around the chain R3 - D2 - battery. The potential at a point with a low, transistor is closed, the light is not lit.

If both points are connected to the earth, at a point with also there will be low potential.

Such schemes can be used in an electronic examiner and other logic circuits, where the output signal will only have simultaneous signals in two or more input channels.

Possible states of the scheme are reflected in the table.

Tatac of truth scheme and

Experiment 19.
Scheme "Or" by units

This scheme is opposite to the previous one. In order to be "0" at the point, it is necessary that at points A and B was also "0", i.e., points A and B must be connected with a negative tire. In this case, the transistor closes, the bulb will go out (Fig. 25).

If now is only one of the points, or in, connect with a negative bus, then at the point with still there will be a high level, i.e. "1", the transistor is open, the light is on.

Fig. 25. Logical element 2Ili on the transistor.

When the point is connected to the negative bus, the current will go through R2, D1 and R3. Through the d2 d2 will not go, as it is included in the direction inverse to the conductivity. At the point C will be about 9 V. The transistor is open, the light is on.

Now the point A connect with a negative bus. Current will go through R1, d2, R3. The voltage at the point C will be about 9 V, the transistor is open, the light is on.

Tatac of truth scheme or

Experiment 20.
Scheme "Not" (inverter)

This experiment demonstrates the operation of the transistor as an inverter - a device capable of changing the polarity of the output signal relative to the input to the opposite. In experiments and the transistor, it was not part of the acting logic schemes, it only served to turn on the light bulb. If the point is to connect with a negative bus, then the potential will fall to, "0", the transistor closes, the light bulb will go out, at point B - high potential. This means a logical "1" (Fig. 26).

Fig. 26. The transistor works as an inverter.

If the point is not connected to the negative tire, i.e. at point A - "1", then the transistor is open, the light is on, the voltage at the point is close to "0" or this is a logical "0".

In this experiment, the transistor is an integral part of a logic circuit and can be used to convert the circuit or or non-diagram and in and non.

The truth table is not a scheme

Experiment 21.
Scheme "and not"

This experiment combines two experiments: 18 - diagram and and 20 - no scheme (Fig. 27).

This scheme functions similarly to the scheme, forming on the basis of the transistor "1" or "0".

Fig. 27. Logical element 2I - not on the transistor.

The transistor is used as an inverter. If "1" appears on the basis of the transistor, then the output point is "0" and vice versa.

If the potentials at the D point are compared with the potentials at the point C, it can be seen that they are inverted.

The truth table of the scheme and is not

Experiment 22.
Scheme "Or-not"

This experiment combines two experiments: - scheme or and - no scheme (Fig. 28).

Fig. 28. Logical element 2Li-not on the transistor.

The scheme functions in the same way as in the experiment 20 (on the basis of the transistor is produced by "0" or "1"). The only difference is that the transistor is used as an inverter: if "1" at the input of the transistor, then "0" at its output and vice versa.

The truth table of the scheme or is not

Experiment 23.
Scheme "And not", assembled on transistors

This scheme consists of two logical circuits not, the collectors of transistors are connected at point C (Fig. 29).

If both points, A and B, connect with a negative tire, their potentials will become equal to "0". Transistors will close, at the point C will be high potential, there will be no light bulb.

Fig. 29. Logical element 2I - not.

If only a point and connect with a negative bus, at a point to a logical "1", the T1 is closed, and the T2 is open, the collector current flows, the light bulb is on, at a point with a logical "0".

If the point is in combining with a negative bus, then the output will also be "0", the light bulb will burn, in this case the T1 is open, the T2 is closed.

And finally, if points A and B have a logical "1" (not connected to the negative tire), both transistors are open. On their collectors "0", the current flows through both transistors, the light burns.

The truth table of the scheme and is not

Experiment 24.
Phone sensor and amplifier

In the experimental scheme, both transistors are used as an amplifier of sound signals (Fig. 30).

Fig. 30. Inductive phone sensor.

The signals are caught and fed to the T1 transistor database using an inductive coil L, then they are enhanced and served in the phone. When you finished collecting the circuit on the board, place the ferrite rod near the phone perpendicular to the incoming wire. It will be heard.

In this scheme, in the future, a ferrite rod with a diameter of 8 mm and a length of 100-160 mm, 600 NNH grade is used as an inductive coil. The winding contains approximately 110 turns of the copper insulated wire with a diameter of 0.15..0.3 mm of the PAL or PEV type.

Experiment 25.
Microphone amplifier

If there is an excess phone (Fig. 31), it can be used instead of the inductance coil in the previous experiment. As a result, we will have a sensitive microphone amplifier.

Fig. 31. Microphone amplifier.

Within the assembled scheme, you can get a semblance of a two-way device. Telephone 1 can be used as a receiving device (connection at point A), and telephone 2 - as an output device (connection at point B). At the same time, the second ends of both phones should be connected to the negative bus.

Experiment 26.
Amplifier for player

Using a gramophone amplifier (Fig. 32), you can listen to the record without breaking the rest of others.

The scheme consists of two cascades of sound amplification. The input signal is a signal that goes from the pickup.

Fig. 32. Amplifier for the player.

In the scheme of the letter A marked with a sensor. This sensor and C2 capacitor are a capacitive voltage divider to reduce the initial volume. The C3 trimmed condenser and C4 condenser are a secondary voltage divider. With C3, the volume is adjusted.

Experiment 27.
"Electronic violin"

Here the multivibrator scheme is designed to create electronic music. The scheme is similar. The main difference is that the transistor database displacement resistor T1 is variable. The resistor 22 com (R2), connected in series with a variable resistor, provides a minimum resistance of the database of the base T1 (Fig. 33).

Fig. 33. Multivibrator to create music.

Experiment 28.
Flashing buzzer Morse

In this scheme, the multivibrator is designed to generate pulses with a tone frequency. The light lights up when the diagram is turned on (Fig. 34).

The phone in this scheme is included in the chain between the T2 transistor collector through the C4 condenser and the negative tire of the board.

Fig. 34. The generator for studying the ABC Morse.

With this scheme, you can practic in the study of the ABC Morse.

If you are not satisfied with the sound of sound, change the C2 and C1 capacitors in places.

Experiment 29.
METRONOME

The metronome is a device for setting the rhythm (tempo), for example, in music. For these purposes, the pendulum was previously used, which gave both visual and auditories of the tempo.

In this diagram, the specified functions perform a multivibrator. The rate of tempo is approximately 0.5 s (Fig. 35).

Fig. 35. Metronome.

Thanks to the telephone and indicator light, there is an opportunity to hear and visually sense the specified rhythm.

Experiment 30.
Sound signaling device with automatic return to its original position

This scheme (Fig. 36) demonstrates the use of a single-man, the operation of which is described in the experiment 14. In the initial state, the T1 transistor is open, and the T2 is closed. The phone here is used as a microphone. Whistle to the microphone (you can just pour) or the lung tapping excites alternating current in the microphone chain. Negative signals, entering the T1 transistor base, close it, and therefore, open the T2 transistor, in the T2 collector circuit, the current appears, and the light bulb lights up. At this time, the C1 condenser is charged through the R1 resistor. The voltage of the charged C2 capacitor is sufficient for opening the transistor T1, i.e. the scheme returns to its original state spontaneously, the light bulb goes out. The breaking time of the bulb is about 4 s. If C2 and C1 capacitors change places, the breaking time of the bulb will increase to 30 s. If the R4 resistor (1 com) is replaced by 470 kΩ, then the time will increase from 4 to 12 s.

Fig. 36. Acoustic signaling device.

This experiment can be represented as a focus that can be shown in the circle of friends. To do this, remove one of the microphones of the phone and put it under the fee near the bulb so that the hole in the board coincides with the microphone center. Now, if you look at the hole in the board, it will seem that you blow on the light bulb and therefore it lights up.

Experiment 31.
Sound signaling device with manual return to its original position

This scheme (Fig. 37) on the principle of action is similar to the previous one, with the only difference, which when switching the scheme does not return automatically into the initial state, and it is done using the Switch B.

Fig. 37. Acoustic signaling device with manual discharge.

The status of the readiness of the circuit or the initial state will be when the T1 transistor is open, the T2 is closed, the lamp does not burn.

A light whistle into the microphone gives a signal that locks the transistor T1, while opening the T2 transistor. The light bulb lights up. It will burn until the T2 transistor closes. To do this, it is necessary to move the database of the T2 transistor to the negative tire ("Earth") using the key V. To such schemes, other actuators can be connected, such as a relay.

Experiment 32.
The simplest detector receiver

A novice radio amateur design of radio receptions should be started with the simplest structures, for example, from a detector receiver, the diagram of which is represented in Fig. 38.

The detector receiver works as follows: electromagnetic waves sent to air radio stations crossing the receiver antenna, supply voltage to it with a frequency corresponding to the frequency of the radio station signal. The induced voltage enters the input circuit L, C1. In other words, this circuit is called resonant, as it is configured in advance to the frequency of the desired radio station. In the resonant circuit, the input signal is intensified in tens of times and then enters the detector.

Fig. 38. Detection receiver.

The detector is assembled on semiconductor diode, which serves to straighten the modulated signal. Low-frequency (sound) component will pass through the headphones, and you will hear speech or music depending on the transfer of this radio station. The high-frequency component of the extended signal, bypassing the headphones, will pass through the C2 condenser to the ground. Capacity C2 capacitor determines the degree of filtering of the high-frequency component of the extended signal. Usually the C2 capacitor capacity is chosen in such a way that it represents a lot of resistance for the sound frequencies, and there was little for the high-frequency component.

As a capacitor C1, any small capacitor variable capacitance can be used with a measurement limits of 10 ... 200 PF. In this constructor, a ceramic trimmed capacitor of the PDA-2 type capacitance from 25 to 150 PF is used to configure the contour.

The inductor L coil has the following parameters: the number of turns is 110 ± 10, the wire diameter is 0.15 mm, the type - PEV-2, the diameter of the frame from the insulating material is 8.5 mm.

ANTENNA

The correctly assembled receiver begins to work immediately when the outer antenna is connected to it, which is a piece of copper wire with a diameter of 0.35 mm, 15-20 m long, suspended on the insulators at some height above the ground. The higher the antenna will be above the earth, the better the reception of radio stations.

Ground

The volume of the reception increases if a grounding is connected to the receiver. Grounding wire should be short and have a small resistance. Its end is connected to the copper pipe going deep into the soil.

Experiment 33.
Low Frequency Detector Receiver

This scheme (Fig. 39) is similar to the previous diagram of the detector receiver with the only difference, which is added here the simplest low frequency amplifier, assembled on the transistor, the low frequency amplifier serves to increase the power of signals prohibited by a diode. The circuit of the oscillating circuit setting is connected to the diode through the C2 capacitor (0.1 μF), and the resistor R1 (100 com) provides a diode constant displacement.

Fig. 39. Detector receiver with a single-stage UNG.

For normal operation of the transistor, the power supply is used by a voltage of 9 V. The R2 resistor is needed in order to ensure the supply of voltage to the transistor base to create the necessary mode of its operation.

For this scheme, as in the previous experiment, an outer antenna and grounding are needed.

Experiment 34.

Simple transistor receiving

The receiver (Fig. 40) differs from the previous one that instead of the diode d, a transistor is installed, which simultaneously works and as a detector of high-frequency oscillations, and as a low frequency amplifier.

Fig. 40. Monolayer receiver.

The detection of a high-frequency signal in this receiver is carried out on the base area - emitter, so this receiver does not require a special detector (diode). The transistor with the oscillatory circuit is associated, as in the previous scheme, through a capacitor with a capacity of 0.1 μF and is unleashed. The C3 condenser serves to filter the high-frequency component of the signal, which is also enhanced by the transistor.

Experiment 35.
Regenerative receiver

This receiver (Fig. 41) regeneration is used to improve the sensitivity and selectivity of the contour. This role is performed by the L2 coil. The transistor in this scheme is incorporated somewhat differently than in the previous one. The voltage of the signal from the input circuit enters the transistor database. The transistor detects and enhances the signal. The high-frequency component of the signal does not immediately go to the filter capacitor C3, and it takes first through the feedback L2 winding, which is on the same core with the contour coil L1. Due to the fact that the coils are located on one core, there is an inductive connection between them, and part of the reinforced voltage of the high-frequency signal from the collector circuit of the transistor comes into the input circuit of the receiver. With the proper onnd of the ends of the Communication coil L2, the feedback voltage coming into the circuit L1 due to the inductive communication coincides with the phase with the signal coming from the antenna, and there is an increase in the signal. The sensitivity of the receiver is increasing. However, with a large inductive connection, such a receiver can turn into a non-teaching oscillation generator, and a sharp whistle listens in phones. To eliminate excessive excitement, it is necessary to reduce the degree of communication between the coils L1 and L2. It is achieved by either the removal of coils from each other, or a decrease in the number of turns of the coil L2.

Fig. 41. Regenerative receiver.

It may happen that feedback does not give the desired effect and reception of stations that are well audible before, when the feedback is introduced at all. This suggests that instead of a positive feedback, a negative and need to be swapped the ends of the L2 coil.

At short distances from the radio station, the described receiver works well without an external antenna, one magnetic antenna.

If the audibility of the radio station is low, the receiver still needs to be connected to the outer antenna.

A receiver with one ferrite antenna must be installed so that the electromagnetic waves coming from the radio station created the largest signal in the oscillating coil. Thus, when you are configured using a radio station with a variable "condenser if the hearing is bad, turn the circuit to receive signals in the phones you need for you.

Experiment 36.
Two-striped regenerative receiver

This scheme (Fig. 42) differs from the previous one that the low frequency amplifier collected on the T2 transistors is used here.

With the help of a two-strip regenerative receiver, we can conduct a large number of radio stations.

Fig. 42. Regenerative receiver with low frequency amplifier.

Although in this designer (set number 2) there is only a coil for long waves, the scheme can work both on medium and short waves, when using the corresponding rapid coils. They can be made by themselves.

Experiment 37.
"Perelelector"

The scheme of this experiment is similar to the Scheme of Experiment 36 without antenna and "Earth".

Tune in to a powerful radio station. Take a fee in your hands (it must be horizontally) and rotate until the sound (signal) or at least decreases to a minimum will disappear. In this position, the ferrite axis accurately indicates the transmitter. If you now turn 90 ° fee, the signals will be well audible. But more precisely, the location of the radio station can be determined by the columatalog method, using the compass to determine the angle in azimuth.

To do this, it is necessary to know the direction of the transmitter from different positions - A and B (Fig. 43, a).

Suppose we are at point A, determined the direction of the transmitter location, it is 60 °. Now we will move to the point in, with the distance of the av. We define the second direction of the transmitter location, it is 30 °. The intersection of two directions and is the location of the transmitting station.

Fig. 43. Scheme of radio station deplementation.

If you have a map with the location of broadcasting stations on it, that is, the ability to accurately determine your location.

Tune in to the station A, let it be located at an angle of 45 °, and then configure to the station B; Its azimuth, for example, is 90 °. Given these corners, spend on the map through points A and in the line, their intersection and will give your location (Fig. 43, b).

In the same way, ships and aircraft are oriented in the process of movement.

Chain control

In order to work reliably during experiments, it is necessary to make sure that the battery is charged, all compounds are clean, and all nuts are reliable. Battery conclusions must be properly connected; When connected, it is necessary to strictly observe the polarity of electrolytic capacitors and diodes.

Check components

Diodes can be tested in; transistors - in; Electrolytic capacitors (10 and 100 μF) - in. You can also check the headphone, connecting it to the battery, - in the headphone will be heard "crackling".

In the last article, we considered a scheme without a bipolar transistor. In order to understand how the transistor works, we will collect a simple regulator of the power of the incandescent light bulb with a two and transistor.

How the transistor works

Let's remember how the transistor behaves. In theory, the bipolar transistor is a controlled resistance between the collector and the emitter, which is controlled by the power of the base current. About all this I wrote more in.

If you submit a transistor like this crane, you can make a small analogy. With the help of one little girl, I can turn on the mad stream of water, which will immediately run through the pipe.

Also do not forget that adjusting the corner of the handle, I can also smoothly adjust the flow of water in the pipe.

I open the crane, the flow of water runs to the full coil:

I closes the crane, water does not run:

What did you remember?

Power control using a transistor

So, I will make a circuit of the power luminosity of the incandescent bulb with the help of the Soviet transistor KT815B. It will look like this:

In the diagram we see the incandescent lamp, the transistor and two resistors. One of them variable. So, the main rule of the transistor: changing current strength in the base chain, we thus change the current strength in the collector's chain, consequently, the power of the lamp itself.

How will all this look like in our scheme? Here I showed two branches. One blue, other red.

As you can see, in the blue chain branch, each other is followed by + 12V - R1 - R2 - the base - emitter - minus power supply. And how do you remember, if the resistors or various consumers (loads) of the chains go on each other consistently, then through all these loads, consumers and resistors proceed same and the same current. Rule of voltage divider. That is, at the moment, for convenience of explanation, I called this strength of current as the current of the base I B.. All the same can be said about the red branch. The current will go on this path: + 12V - the light bulb - the collector - the emitter - minus power supply. It will flow a current collector I K..

So why did we disassemble these branches of the chain now? The fact is that the base current flows through the database and emitter I B. which also flows through a variable resistor R1 and resistor R2. A collector current flows through the emitter collector IK which also flows through the incandescent light bulb.

Well, now the most interesting thing: the collector current depends on which current current current flows through the Base-Emitter. That is, adding the base current, we are therefore adding the collector current. And since the collector current we have become more, it means that the current force has become more through the light bulb, and the light bulb caught up even brighter. Driving a weak current of the base, we can control the current collector current.This is the principle of operation of the bipolar transistor.

How do we now regulate the strength of the current through the Base-Emitter? Remember the Ohm law: I \u003d u / r. Consequently, adding or having reduced the resistance value in the base chain, we thus can change the strength of the base current! Well, it will already adjust the strength of the current in the collector's chain. It turns out by changing the value of the variable resistor, we thus change the glow of the light bulb ;-)

And one more small nuance.

As you noticed in the diagram there is a R2 resistor. What is it needed for? The thing is that it may be a breakdown of the transition base-emitter. Or, in simple language, he will burn. If it were not, then when resisting resistance on a variable resistor R1 to zero, we would smell the base-emitter. Therefore, so that this is not, we must select a resistor, which would be with resistance to R1 to zero OM, would limit the strength of the current to the database so that it is not smelted.

It turns out, we must pick up the current strength on the base so that the light is shone to full brightness, but at the same time the transition base-emitter would be whole. If you say the electronics language - we must choose such a resistor that would drive the transistor to the border of saturation, but nothing more.

Work of the real scheme

Well, now the matter is for practice. We collect the scheme in real life:

I wig a variable resistor and seek the light bulb for all the heat:

Clear more sensitive and light bulb shines on the floor of the heat:

I unscrew the variable resistor to the stop and the light bulb goes out:

Instead of a light bulb, you can take any other load, such as a fan from the computer. In this case, by changing the value of the variable resistor, I can control the frequency of rotation of the fan, thereby reducing or adding the stream of air flow.

Here the fan does not spin, since I put great resistance on a variable resistor:

Well, here, twisting the variable resistor, I can already adjust the fan speed:

It can be said that the finished scheme turned out to blow himself a hot summer day ;-). It became cold - he lost turnover, it became too hot - added ;-)

Wailed teapots-electronics can say: "Why was it all so much to complicate? Was it easier to simply take a variable resistor and connect sequentially with the load?

Yes, you can.

But there must be some conditions. We assume our incandescent lamp of high power, which means the current of the current in the chain will also be decent. In this case, the variable resistor must be high power, since when unscrewed until it stops towards small resistance, a high current will run through it. We remember the formula of the outdated power on the load: P \u003d i 2 R. Variable resistor scorit (checked more than once on its own experience).

In the diagram with the transistor, the entire burden of responsibility, then you mean all the power of the dispersion, the transistor takes over. In the diagram with the transistor, the variable resistor will not be spilled, since the current is in the base chain in tens, and even hundreds of times less (depending on the beta of the transistor) than the current of the current through the load, in our case through the light bulb.

Break the maximum transistor only when we adjust the load power by half. In this case, half of the cut-off power in the load will scatter on the transistor. Therefore, if you regulate a powerful load, then for a start, ask the transistor dispersion power as the power dissipation and, if necessary, do not forget to put transistors for radiators.

Summary

The main purpose of the transistor is to control the high current with a small current, that is, with the help of a small base current, we can adjust a decent collector current.

There is a critical value of the base current that cannot be exceeded, otherwise the transition of the base-emitter will burn. Such a current strength through the database occurs if the potential on the base is more than 5 volts in direct displacement. But it is better not even close to such a value. Also do not forget to open the transistor, there must be a potential at the base than 0.6-0.7 volts for a silicon transistor.

The database resistor is used to limit the flowing current through the emitter base. Its value is chosen depending on the mode of operation of the scheme. Basically, it is the border of the saturation of the transistor, in which the collector current begins to take its maximum values.

When designing a scheme, do not forget that excessive power dissipates on the transistor. The most gentle mode is the cut-off and saturation mode, that is, the lamp is either not lit at all, or on the entire power. The greatest power will be highlighted on the transistor if the lamp is lit into the heat.

In this article we will try to describe principle of operation The most common type of transistor is bipolar. Bipolar transistor It is one of the main active elements of radio-electronic devices. The purpose of it is to work to enhance the power of the electrical signal of the incoming to its input. Power gain is carried out by an external energy source. The transistor is a radio electron component with three conclusions.

Constructive feature of the bipolar transistor

For the production of a bipolar transistor, a semiconductor of a hole or electronic type of conductivity is needed, which is obtained by diffusion by either acceptor impurities. As a result, on both sides of the base, areas are formed with polar conduction species.

Bipolar conductivity transistors are two species: N-P-N and P-N-P. The rules of work, which is subordinate to the bipolar transistor, having N-P-N conductivity (for P-N-P, it is necessary to change the polarity of the applied voltage):

1. Positive potential at the collector is of greater value compared to the emitter.
2. Any transistor has its maximum permissible parameters of IB, IK and UCE, the excess of which is in principle unacceptable, as this can lead to the destruction of the semiconductor.
3. Conclusions Base - Emitter and Base - Collector Function like diodes. As a rule, a diode in the direction of the base - the Emitter is open, and in the direction of the base - the collector is shifted in the opposite direction, that is, the incoming voltage interferes with the flow of electrical current through it.
4. If paragraphs with 1 to 3 are made, then the current of the IK is directly proportional to the current of the IB and has the form: IK \u003d HE21 * IB, where HE21 is a coefficient of strengthening current. This rule characterizes the main quality of the transistor, namely, the fact that the small current of the base has a powerful current collector.

For different bipolar transistors of the same series, the HE21 indicator may differ fundamentally from 50 to 250. Its value also depends on the flowing current of the collector, the voltage between the emitter and the collector, and on the ambient temperature.

We study rule number 3. It follows from it that the voltage applied between the emitter and the base should not be significantly increased, since if the base voltage is larger than the emitter by 0.6 ... 0.8 V (direct diode voltage), it will appear extremely high current. Thus, in the operating voltage transistor on the emitter and the base are interrelated by the formula: UB \u003d UE + 0.6V (UB \u003d UE + UBE)

Recall once again that all these moments refer to transistors having N-P-N conductivity. For the type P-N-P, everything should be changed to the opposite.

It should also be paid to the fact that the collector current does not have connection with the conduction of the diode, since, as a rule, the reverse voltage comes to the diode. In addition, the current flowing through the collector is very little depends on the potential at the collector (this diode is similar to a small current source)

When the transistor is turned on in the amplification mode, the emitter transition is open, and the collector transition is closed. This is obtained by connecting power sources.

Since the emitter transition is open, then an emitter current will be held through it, arising from the transition of holes from the base to the emitter, as well as electrons from the emitter to the database. So, the emitter current contains two components - hole and electronic. The injection coefficient determines the effectiveness of the emitter. Injection charges refer to the transfer of charge carriers from the zone, where they were main in the zone where they are made non-mining.

In the database, electrons are recombined, and their concentration in the database is replenished from the plus of the EE source. As a result, there will be a rather weak current in the electrical circuit. The remaining electrons that did not have time to recombine in the database, under the accelerating effect of the location of the locked collector transition, as non-core media, will move to the collector, creating a collector current. The transfer of charge carriers from the zone where they were miner, to the zone where they become the main, referred to as the extraction of electrical charges.

Transistor (Transistor, English) - triode, from semiconductor materials, with three outputs, the main property of which is a relatively low input signal to control the significant current at the output of the chain. In radio components from which modern complex electrical appliances are collected, field transistors are used. Their properties allow you to solve problems on the shutdown or turning on the current in the circuit circuit of the printed circuit board, or enhancing it.

What is a field transistor

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

Contacts:

Field transistor with P - p transition - a special type of transistors that serve to control the current.

It differs from the simple usual the fact that the current in it passes, without crossing the zone P - n of the transition, the zones formed on the boundaries of these two zones. The size of P - N zone is adjustable.

Field transistors, their types

Field transistors with P - p transition shall be divided into classes:

1. By type of channel of the conductor: n or p. A sign, polarity, control signal depends on the channel. It must be opposite by the sign N -one.
2. According to the structure of the device: diffuse, alloy in P - N - transition, with a shutter, thin-film.
3. By contact numbers: 3 and 4-pin. In the case of a 4-pin instrument, the substrate also executes the role of the shutter.
4. According to the materials used: Germany, silicon, Gluff Arsenide.

Classes are divided according to the principle of operation:

• device under the control of P - N of the transition;
• a device with an isolated shutter or with a barrier of Schottky.

Field transistor, principle of operation

It is easily like a field transistor with a controlling Red transition, one can say so: radio component consists of two zones: P - transition and P - transition. By zone p flowing electric current. Zone P - overlapping the zone of a kind of valve. If it is strongly pressed, it overlaps the zone to pass the current And it passes less. Or, if the pressure is reduced more. Such pressure is carried out by increasing the voltage on the shutter contact located in the r.

The device with the control r - n channel transition is a semiconductor plate with electrical conductivity of one of these types. Contacts are connected to the ends of the plates: stock and source, in the middle - the contact of the shutter. The device action is based on the variability of the thickness of the space of the rift of the transition. Since there are almost no mobile chargers in the locking area, its conductivity is zero. In the semiconductor plate, in the area not under the influence of the locking layer, the conductive channel is created. When the negative voltage is submitted relative to the source, the stream is created on the shutter, according to which the charge carriers expire.

In the case of an isolated shutter, it is a thin layer of dielectric. This type of device works on the principle of electric field. To destroy its enough small electricity. Therefore, to protect against static voltage, which can reach thousands of volts, create special instrument housings - they allow you to minimize the effects of viral electricity.

Why do you need a field transistor

Considering the work of complex electronic equipment as the work of the field transistor (as one of the components of the integrated circuit) is difficult to imagine that the main directions of his work five:

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

On a simple example, the operation of the transistor, as a switch, can be represented as a microphone layout with a light bulb. The microphone catches the sound, an electric current appears from this. It enters the locked field transistor. The current includes the device, includes an electrical circuit to which the light is connected. The light lights up when the sound is captured by the microphone, but burns due to a power source that is not associated with a microphone and more powerful.

Modulation is applied To control the information signal. The signal controls the frequency of oscillation. Modulation is used for a high-quality sound signal in the radio, to transmit sound rows in television transmissions, broadcast color and high quality television signal. It is used everywhere where work is required with high quality material.

As amplifier The field transistor simplifically works like this: graphically any signal, in particular, sound row, can be represented as a broken line, where its length is time, and the height of the beam is the sound frequency. To enhance the sound to radio metal, a powerful voltage is supplied, which acquires the necessary frequencies, but with more large values, due to the supply of a weak signal to the control contact. In other words, the device proportionally redraws the initial line, but with higher peak values.

The use of field transistors

The first instrument in the sale of a field transistor with a P-N control transition was used, was hearing aid. His appearance was recorded in the fifties of the last century. In an industrial scale, they were used in telephone stations.

In the modern world, devices are used in all electrical engineering. Thanks to the small size and variety of characteristics of the field transistor, it is possible to meet it in the kitchen appliance, audio and television technique, computers and electronic children's toys. They are used in signaling systems as security mechanisms and fire alarms.

At the factories, transistor equipment is applied for power regulators machines. In transport from the work of equipment on trains and locomotives, to the fuel injection system for private cars. In housing and communal services from dispatching systems, to outdoor lighting systems.

One of the most important areas of transistors - processing production. In fact, the entire processor consists of a variety of miniature radio components. But when moving to the frequency of operation above is 1.5 GHz, they are avalanchely begin to consume energy. Therefore, processor manufacturers went along the path of multi-core, and not by increasing the clock frequencies.

Pros and cons of field transistors

Field transistors with their characteristics left far behind other types Devices. Wide use they found in integrated circuits as switches.

• cascade of parts consumes little energy;
• strengthening higher than in other species;
• high noise immunity is achieved by the lack of current flow in the gate;
• higher turning on and off speed - they can work on the frequencies inaccessible to other transistors.

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

The characteristics of semiconductor materials taken as the basis of field transistors allowed apply devices in everyday life and production. Based on the college transistors created household appliances in the usual form for a modern man. The processing of high-quality signals, the production of processors and other high-precision components is impossible without the achievements of modern science.