Application of a transistor generator physics. Transistor generator

Free vibrations always damp due to energy losses (friction, environmental resistance, resistance of electric current conductors, etc.). Meanwhile, both in technology and in physical experiments, undamped oscillations are urgently needed, the periodicity of which remains the same as long as the system oscillates at all. How are such oscillations obtained? We know that forced oscillations, in which energy losses are replenished by the work of a periodic external force, are undamped. But where take an external periodic force? After all, it, in turn, requires a source of some kind of undamped oscillations.

Undamped oscillations are created by devices that themselves can maintain their oscillations due to some constant source of energy. Such devices are called self-oscillating systems. In Fig. 55 shows an example of an electromechanical device of this kind. The weight hangs on a spring, the lower end of which is immersed in a cup of mercury when this spring pendulum oscillates. One pole of the battery is connected to the spring at the top, and the other to the cup of mercury. When the load is lowered, the electrical circuit is closed and current flows through the spring. Thanks to the magnetic field of the current, the coils of the spring begin to attract each other, the spring is compressed, and the load receives an upward push. Then the contact is broken, the coils stop tightening, the load falls down again, and the whole process is repeated again.

Thus, the oscillation of a spring pendulum, which would die out on its own, is maintained by periodic shocks, caused by the oscillation of the pendulum itself. With each push, the battery releases a portion of energy, part of which is used to lift the load. The system itself controls the force acting on it and regulates the flow of energy from the source - the battery. The oscillations do not die out precisely because during each period just as much energy is taken from the battery as is spent during the same time on friction and other losses. As for the period of these undamped oscillations, it practically coincides with the period of natural oscillations of the load on the spring, i.e., it is determined by the stiffness of the spring and the mass of the load.

In the same way, undamped oscillations of a hammer occur in an electric bell, with the only difference being that in it periodic shocks are created by a separate electromagnet that attracts an armature mounted on the hammer. In a similar way, one can obtain self-oscillations with sound frequencies, for example, by exciting undamped oscillations of a tuning fork (Fig. 56). When the legs of the tuning fork move apart, a contact is made 1; through the electromagnet winding 2 current passes and the electromagnet pulls the legs of the tuning fork. In this case, the contact opens, and then the entire cycle is repeated. The phase difference between the oscillation and the force that it regulates is extremely important for the occurrence of oscillations. Let's transfer the contact 1 from the outside of the tuning fork leg to the inside. The closure now occurs not when the legs diverge, but when the legs come closer, i.e., the moment when the electromagnet is turned on is advanced by half a period compared to the previous experiment. It is easy to see that in this case the tuning fork will be compressed all the time by a continuously switched on electromagnet, i.e., oscillations will not occur at all.

Electromechanical self-oscillating systems are used very widely in technology, but purely mechanical self-oscillating devices are no less common and important. It is enough to point to any clock mechanism. The undamped oscillations of a pendulum or a clock balancer are supported by the potential energy of a raised weight or by the elastic energy of a wound spring.

Self-oscillations are also vibrations of a string under the action of a bow (in contrast to the free vibrations of a string on a piano, harp, guitar and other non-bowed string instruments, excited by a single push or jerk); Self-oscillations include the sound of wind musical instruments, the movement of the piston of a steam engine, and many other periodic processes.

A characteristic feature of self-oscillations is that their amplitude is determined by the properties of the system itself, and not by the initial deflection or push, as in free oscillations. If, for example, the pendulum of a clock is deflected too much, then the friction losses will be greater than the energy input from the winding mechanism, and the amplitude will decrease. On the contrary, if the amplitude is reduced, then the excess energy imparted to the pendulum by the running wheel will cause the amplitude to increase. The amplitude at which energy consumption and supply are balanced will be automatically established.

Devices, collectively called self-oscillating systems, are characterized by the following distinctive properties.

Self-oscillating systems are capable of generating undamped oscillations. These oscillations can be harmonic (sinusoidal) or more complex in shape, but they can continue indefinitely until the elements forming the system fail.

Self-oscillating systems differ from an oscillatory circuit with a resistance equal to zero. Such a circuit represents an extreme case that is unattainable in practice. Self-oscillating systems are real devices whose resistance is not zero.

In self-oscillating systems, undamped oscillations arise under the influence of processes occurring within the system, and no external influences are required to maintain them. In this respect, self-oscillations are radically different from forced oscillations, which can also be undamped, but for their existence they require periodic external influences (in mechanics - external forces, in electricity - externally applied voltages).

Self-oscillating systems include an energy source (in the case of mechanical vibrations - a compressed spring, a raised load, etc., in the case of electrical vibrations - a battery or other current source). This source is periodically turned on by the system itself and introduces a certain energy into it, compensating for losses due to the release of Joule-Lenz heat, which makes the oscillations undamped.

Since oscillations in self-oscillating systems are established under the influence of processes occurring within the system, they arise spontaneously (self-excitation), under the influence of random small influences that bring the system out of equilibrium (fluctuations). The small oscillations that arise spontaneously increase, and eventually steady oscillations are formed in the system, the properties of which (frequency, intensity, shape) are determined by the parameters of the system and do not depend on the initial conditions.

How to create undamped oscillations in a circuit? It is known that if the capacitor of an oscillatory circuit is charged, then damped oscillations will appear in the circuit. At the end of each oscillation period, the charge on the capacitor plates is less than at the beginning of the period. The total charge, of course, is conserved (it is always zero), but the positive charge of one plate and the negative charge of the other decrease by values equal in magnitude. As a result, the oscillation energy decreases, since it is proportional to the square of the charge on one of the capacitor plates. To prevent the oscillations from dying out, it is necessary to compensate for the energy losses for each period.

You can replenish energy in the circuit by recharging the capacitor. To do this, you must periodically connect the circuit to a constant voltage source. The capacitor should be connected to the source only during those time intervals when the plate connected to the positive pole of the source is positively charged, and the plate connected to the negative pole is negatively charged (Fig. 4.21). Only in this case will the source recharge the capacitor, replenishing its energy.

If the switch is closed at the moment when the plate connected to the positive pole of the source has a negative charge, and the plate connected to the negative pole has a positive charge, then the capacitor will be discharged through the source (Fig. 4.22). The energy of the capacitor will decrease.

Consequently, a constant voltage source constantly connected to a circuit capacitor cannot support undamped oscillations in it, just as a constant force cannot support mechanical oscillations. During half the period, energy enters the circuit, and during the next half of the period it returns to the source. Undamped oscillations will be established in the circuit only if the source is connected to the circuit during those time intervals when energy can be transferred to the capacitor. To do this, it is necessary to ensure automatic operation of the key (or valve, as it is often called). At high oscillation frequencies, the key must have reliable performance. A transistor is used as such an almost inertia-free switch.

A transistor is made up of three different semiconductors: an emitter, a base, and a collector. The emitter and collector have the same majority charge carriers, such as holes (it is a p-type semiconductor), and the base has opposite sign majority carriers, such as electrons (an n-type semiconductor). A schematic representation of the transistor is shown in Figure 4.23.

Operation of a generator using a transistor. A simplified transistor oscillator circuit is shown in Figure 4.24. The oscillatory circuit is connected in series with a voltage source and a transistor in such a way that a positive potential is applied to the emitter and a negative potential to the collector. In this case, the emitter-base transition (emitter junction) is direct, and the base-collector transition (collector junction) is reverse, and no current flows in the circuit. This corresponds to the open switch in Figures 4.21, 4.22.

In order for a current to arise in the circuit circuit and recharge the circuit capacitor during oscillations, it is necessary to provide the base with a potential negative relative to the emitter, and during those time intervals when the upper (see Fig. 4.24) capacitor plate is positively charged and the lower one is negatively charged. This corresponds to the closed key in Figure 4.21.

During time intervals when the upper plate of the capacitor is negatively charged and the lower plate is positively charged, there should be no current in the circuit circuit. To do this, the base must have a positive potential relative to the emitter.

Thus, to compensate for the loss of oscillation energy in the circuit, the voltage at the emitter junction must periodically change sign in strict accordance with voltage fluctuations in the circuit. What is needed, as they say, is feedback.

The feedback in the generator under consideration is inductive. A coil of inductance Lsv is connected to the emitter junction, inductively coupled to the coil of inductance L of the circuit. Oscillations in the circuit due to electromagnetic induction excite voltage fluctuations at the ends of the coil, and thereby at the emitter junction. If the phase of the voltage oscillations at the emitter junction is selected correctly, then the “jokes” of current in the circuit circuit act on the circuit at the required time intervals, and the oscillations do not die out. On the contrary, the amplitude of oscillations in the circuit increases until the energy losses in the circuit are exactly compensated by the supply of energy from the source. This amplitude is greater, the higher the source voltage. An increase in voltage leads to increased “jokes” of current that recharges the capacitor.

Generators using transistors are widely used not only in many radio devices: radio receivers, transmitting radio stations, amplifiers, etc., but also in modern electronic computers.

Basic elements of a self-oscillating system. Using the example of a transistor generator, we can highlight the main elements characteristic of many self-oscillating systems (Fig. 4.25).

1. An energy source that maintains undamped oscillations (in a transistor generator this is a constant voltage source).

2. An oscillatory system is that part of a self-oscillating system in which oscillations occur directly (in a transistor-based generator this is an oscillatory circuit).
3. The device that regulates the supply of energy from the source to the oscillatory system is a valve (in the generator under consideration, the role of the valve is played by a transistor).
4. A device that provides feedback with the help of which the oscillatory system controls the valve (in the transistor generator there is an inductive coupling of the circuit coil with the coil in the emitter-base circuit).

Questions: (MAKE A SUMMARY IN YOUR NOTEBOOK BY ANSWERING THEM!)

1. What is a self-oscillating system?

2. What is the difference between self-oscillations and forced and free oscillations?

3. How does a transistor work?

4. What is the role of the transistor in the generation of self-oscillations?

5. How is feedback carried out in a transistor generator?

6. Indicate the main elements of a self-oscillating system.

7. What oscillations are called undamped?

8. What oscillations are called forced?

9. Describe how self-oscillations of a spring pendulum occur.

10. Where are self-oscillating systems used?

11. Indicate a characteristic feature of self-oscillations.

12. Indicate the properties of self-oscillating systems (according to points 1,2,3 and so on, as many as there are)

13. What role does the energy source play in the composition of a self-oscillating system?

14. Indicate the reasons leading to the damping of oscillations (write it yourself, not in this text).

15. Draw a diagram and describe the process of creating continuous oscillations in the circuit.

16. What is the transistor used for in a generator?

17. Why is feedback needed?

18. Draw a diagram and describe step by step the process of operation of a transistor generator.

Problems on the topic “Electrical Oscillations” (SEPARATE MARK FOR SOLUTION)

1.1259. A flat-plate capacitor consists of two round plates with a diameter of 8 cm. A glass plate 5 mm thick is sandwiched between the plates. The capacitor plates are connected through a coil with an inductance of 0.02 H. Determine the frequency of oscillations occurring in this circuit.

2. 1260. The oscillatory circuit consists of a coil with an inductance of 0.003 H and a flat capacitor. The capacitor plates in the form of disks with a radius of 1.2 cm are located at a distance of 0.3 mm from each other. Determine the period of natural oscillations of the circuit. What will the oscillation period be if the capacitor is filled with a dielectric with a dielectric constant of 4?

3. 1261. A coil with an inductance of 30 μH is connected to a parallel-plate capacitor with an area of plates of 0.01 m and a distance between them of 0.1 mm. Find the dielectric constant of the medium filling the space between the plates if the circuit is tuned to a frequency of 400 kHz.

4. 1262. Within what limits should the electrical capacity of the capacitor in the oscillatory circuit change so that oscillations with a frequency of 400 to 500 Hz can occur in it? The inductance of the loop coil is 16 mH.

5. 1263. Within what limits should the inductance of the oscillating circuit coil change so that oscillations with a frequency of 400 to 500 Hz can occur in it? The capacitance of the capacitor is 10 nF.

Content:

The purpose of the lesson: form an idea of self-oscillations; a variety of frequencies are generated using self-oscillating systems; without them, modern radio communications and television would be impossible.

Progress

Checking homework by filling out the table

— On the cards distributed to students, the correct answers are randomly located on the right side; on the left side are written formulas, laws, expressions of quantities on the topic studied.

Within 7 minutes you need to write down the correct answer codes and hand in the work to the teacher.

	Magnetic field energy		Im=Um/R
	Electric field energy		XC= 1/ωC
	Total energy of the oscillatory circuit
	The basic equation describing free oscillations in a circuit		Im= qmω
	Thomson's formula		u= Umsinωt
	Law of change of electric charge		T= 2π/ω0= QUOTE
	Law of change in current strength		q′′= — q/ LC
	Current amplitude		I= Im/QUOTE
	Law of voltage change		XL = ωL
	Magnetic induction flux		q= qmcosω0t
	Active resistance in an electrical circuit with a resistor		W=QUOTE +QUOTE
	RMS current value		Ф= BScosωt
	RMS voltage		I =Imsin(ωt+φ)
	Capacitance formula		R= Um/Im
	Inductive reactance formula
	Current amplitude at resonance		Wk= Li2/2
	Power in an electrical circuit with a resistor		U=Um/QUOTE

Answer code: 1- 16; 2- 3; 3-11; 4-7; 5-6; 6-10; 7-13; 8- 4; 9-5; 10-12; 11-14; 12-8; 13-17; 14- 2; 15-9; 16- 1; 17-15/

Learning new material

Repetition of mechanical self-oscillations.

1. Self-oscillating systems.

If in a system in which free electromagnetic oscillations can occur,

place an energy source and the system itself would regulate the supply of energy in portions, then undamped oscillations will appear.

The systems are called self-oscillating, if undamped oscillations are created in them due to the supply of energy from a source inside the system.

A transistor generator is a self-oscillating system.

2. How to create undamped oscillations in a circuit?

It is necessary to ensure automatic operation of the valve or key.

The valve must have a large...
speed. This work of the inertia-free valve is performed by a transistor, which consists of 3 semiconductors: a collector,

emitter and base. The emitter and collector have the same majority charge carriers;

the main carriers of the base have the opposite sign.

3. Operation of a generator using a transistor.

In the diagram we see that the oscillating circuit is connected in series with a voltage source, and then there is a transistor.

A negative potential is applied to the collector, and a positive potential is applied to the emitter.

The base-collector transition is reverse (no current flows in the circuit); in this case, the emitter-base transition turns out to be direct. Which corresponds to the open key in the diagrams.

In order for current to appear in the circuit and charge the capacitor, it is necessary to provide the base with a negative potential relative to the emitter. This corresponds to the closed key in the diagram. To compensate for energy losses in the circuit, the voltage at the emitter junction

must constantly change sign to provide feedback.

In this case, feedback occurs due to the inductive coupling of the coils. One of the nicks is located in the circuit, the other is connected to the emitter junction.

To prevent oscillations in the circuit from damping, it is necessary to select the phase of voltage oscillations at the emitter junction so that the current “jokes” act on the circuit at the required time intervals.

The oscillation frequency in the circuit depends on the inductance of the coil and the capacitance of the capacitor.

ω0=1 / QUOTE

The lower the inductance and capacitance, the higher the oscillation frequency

Transistor generators are widely used in radio devices and electronic computers.

4. Basic elements of a self-oscillating system.

Let us highlight the main elements used in many self-oscillating systems.

Reinforcing the topic studied

1. Where do self-oscillations occur?

2. How do self-oscillations differ from free and forced oscillations?

3. Describe the role of the transistor in creating self-oscillations?

4. What is feedback and how is it implemented in a transistor generator?

5. Identify the elements of a self-oscillating system.

Let's summarize the lesson

Homework: § 36, rep. §34, no. 971, 976.

Operation of a generator using a transistor. 1. In order for a current to arise in the circuit and recharge the circuit capacitor during oscillations, it is necessary to provide the base with a “-” potential relative to the emitter, and during those time intervals when the upper plate of the capacitor is charged “+” and the bottom plate is charged “-”. This corresponds to a closed key. 2. To compensate for the loss of oscillation energy in the circuit, the voltage at the emitter junction must periodically change sign in strict accordance with voltage fluctuations in the circuit. 3. Feedback is needed.

Slide 11 from the presentation “Self-oscillations” for physics lessons on the topic “Types of vibrations”

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Types of vibrations

“Damped oscillations” - Consequently, the movement is aperiodic (non-periodic) in nature - the system removed from the equilibrium position returns to the equilibrium position without oscillating. ceases to be periodic. Topic: Damped oscillations. Free damped oscillations in an electric oscillatory circuit; 26.27.

“Self-oscillations” - Generator of high-frequency electromagnetic oscillations. The term self-oscillations was introduced into Russian terminology by A. A clock as a self-oscillating system. Self-oscillations are undamped oscillations in a dissipative dynamic system with nonlinear feedback, supported by the energy of a constant, that is, non-periodic external influence.

“Physics “Harmonic Oscillations”” - Damping coefficient. Movement from some starting point to returning to the same point. Damped oscillations are non-periodic oscillations. Charge on the capacitor plate. Maximum values. Attenuation is usually characterized by a logarithmic decrement. Another type of resonance. Equation of damped oscillations in a circuit.

“Harmonic oscillations and pendulums” - Free oscillations. Pendulum. Processes. Let's divide the equation. Periodic oscillatory motion. The concept of a rotating vector. Energy of harmonic oscillatory motion. Pendulums. Liver. Oscillatory system. Material point. Harmonic oscillation with an initial phase. Acceleration during harmonic oscillations.

“Harmonic oscillations” - The rotating amplitude vector fully characterizes the harmonic oscillation. 3. The phase difference changes over time in an arbitrary manner. The amplitude A of the resulting oscillation depends on the difference in the initial phases. Using the rule of vector addition, we find the total amplitude of the resulting oscillation: Such oscillations are called linearly polarized.

Radio amateurs need to receive various radio signals. This requires the presence of a low-frequency and high-frequency generator. This type of device is often called a transistor generator due to its design feature.

Additional Information. A current generator is a self-oscillating device created and used to generate electrical energy in a network or convert one type of energy into another with a given efficiency.

Self-oscillating transistor devices

The transistor generator is divided into several types:

according to the frequency range of the output signal;
by type of signal generated;
according to the action algorithm.

The frequency range is usually divided into the following groups:

30 Hz-300 kHz – low range, designated low;
300 kHz-3 MHz – medium range, designated midrange;
3-300 MHz – high range, designated HF;
more than 300 MHz – ultra-high range, designated microwave.

This is how radio amateurs divide the ranges. For audio frequencies, they use the range 16 Hz-22 kHz and also divide it into low, medium and high groups. These frequencies are present in any household sound receiver.

The following division is based on the type of signal output:

sinusoidal – a signal is issued in a sinusoidal manner;
functional – the output signals have a specially specified shape, for example, rectangular or triangular;
noise generator – a uniform frequency range is observed at the output; ranges may vary depending on consumer needs.

Transistor amplifiers differ in their operating algorithm:

RC – main area of application – low range and audio frequencies;
LC – main area of application – high frequencies;
Blocking oscillator - used to produce pulse signals with high duty cycle.

Picture on electrical diagrams

First, let's consider obtaining a sinusoidal type of signal. The most famous oscillator based on a transistor of this type is the Colpitts oscillator. This is a master oscillator with one inductance and two series-connected capacitors. It is used to generate the required frequencies. The remaining elements provide the required operating mode of the transistor at direct current.

Additional Information. Edwin Henry Colpitz was the head of innovation at Western Electric at the beginning of the last century. He was a pioneer in the development of signal amplifiers. For the first time he produced a radiotelephone that allowed conversations across the Atlantic.

The Hartley master oscillator is also widely known. It, like the Colpitts circuit, is quite simple to assemble, but requires a tapped inductance. In the Hartley circuit, one capacitor and two inductors connected in series produce generation. The circuit also contains an additional capacitance to obtain positive feedback.

The main area of application of the devices described above is medium and high frequencies. They are used to obtain carrier frequencies, as well as to generate low-power electrical oscillations. Receiving devices of household radio stations also use oscillation generators.

All of the listed applications do not tolerate unstable reception. To do this, another element is introduced into the circuit - a quartz resonator of self-oscillations. In this case, the accuracy of the high-frequency generator becomes almost standard. It reaches millionths of a percent. In receiving devices of radio receivers, quartz is used exclusively to stabilize reception.

As for low-frequency and sound generators, there is a very serious problem here. To increase the tuning accuracy, an increase in inductance is required. But an increase in inductance leads to an increase in the size of the coil, which greatly affects the dimensions of the receiver. Therefore, an alternative Colpitts oscillator circuit was developed - the Pierce low-frequency oscillator. There is no inductance in it, and in its place a quartz self-oscillation resonator is used. In addition, the quartz resonator allows you to cut off the upper limit of oscillations.

In such a circuit, the capacitance prevents the constant component of the base bias of the transistor from reaching the resonator. Signals up to 20-25 MHz, including audio, can be generated here.

The performance of all the devices considered depends on the resonant properties of the system consisting of capacitances and inductances. It follows that the frequency will be determined by the factory characteristics of the capacitors and coils.

Important! A transistor is an element made from a semiconductor. It has three outputs and is capable of controlling a large current at the output from a small input signal. The power of the elements varies. Used to amplify and switch electrical signals.

Additional Information. The presentation of the first transistor was held in 1947. Its derivative, the field-effect transistor, appeared in 1953. In 1956 The Nobel Prize in Physics was awarded for the invention of the bipolar transistor. By the 80s of the last century, vacuum tubes were completely forced out of radio electronics.

Function transistor generator

Functional generators based on self-oscillation transistors are invented to produce methodically repeating pulse signals of a given shape. Their form is determined by the function (the name of the entire group of similar generators appeared as a result of this).

There are three main types of impulses:

rectangular;
triangular;
sawtooth.

A multivibrator is often cited as an example of the simplest LF producer of rectangular signals. It has the simplest circuit for DIY assembly. Radio electronics engineers often begin with its implementation. The main feature is the absence of strict requirements for the ratings and shape of transistors. This occurs due to the fact that the duty cycle in a multivibrator is determined by the capacitances and resistances in the electrical circuit of transistors. The frequency on the multivibrator ranges from 1 Hz to several tens of kHz. It is impossible to organize high-frequency oscillations here.

Obtaining sawtooth and triangular signals occurs by adding an additional circuit to a standard circuit with rectangular pulses at the output. Depending on the characteristics of this additional chain, rectangular pulses are converted into triangular or sawtooth pulses.

Blocking generator

At its core, it is an amplifier assembled on the basis of transistors arranged in one cascade. The scope of application is narrow - a source of impressive, but transient in time (duration from thousandths to several tens of microseconds) pulse signals with large inductive positive feedback. The duty cycle is more than 10 and can reach several tens of thousands in relative values. There is a serious sharpness of the fronts, practically no different in shape from geometrically regular rectangles. They are used in the screens of cathode-ray devices (kinescope, oscilloscope).

Pulse generators based on field-effect transistors

The main difference between field-effect transistors is that the input resistance is comparable to the resistance of electronic tubes. Colpitts and Hartley circuits can also be assembled using field-effect transistors, only the coils and capacitors must be selected with the appropriate technical characteristics. Otherwise, field-effect transistor generators will not work.

The circuits that set the frequency are subject to the same laws. For the production of high-frequency pulses, a conventional device assembled using field-effect transistors is better suited. The field effect transistor does not bypass the inductance in the circuits, so the RF signal generators operate more stably.

Regenerators

The LC circuit of the generator can be replaced by adding an active and negative resistor. This is a regenerative way to obtain an amplifier. This circuit has positive feedback. Thanks to this, losses in the oscillatory circuit are compensated. The described circuit is called regenerated.

Noise generator

The main difference is the uniform characteristics of low and high frequencies in the required range. This means that the amplitude response of all frequencies in this range will not be different. They are used primarily in measurement equipment and in the military industry (especially aircraft and rocketry). In addition, the so-called “gray” noise is used to perceive sound by the human ear.

Simple DIY sound generator

Let's consider the simplest example - the howler monkey. You only need four elements: a film capacitor, 2 bipolar transistors and a resistor for adjustment. The load will be an electromagnetic emitter. A simple 9V battery is enough to power the device. The operation of the circuit is simple: the resistor sets the bias to the base of the transistor. Feedback occurs through the capacitor. The tuning resistor changes the frequency. The load must have high resistance.

With all the variety of types, sizes and designs of the considered elements, powerful transistors for ultra-high frequencies have not yet been invented. Therefore, generators based on self-oscillation transistors are used mainly for the low and high frequency ranges.

Video

« Physics - 11th grade"

Forced oscillations occur under the influence of alternating voltage generated by generators at power plants.
Such generators cannot create high-frequency oscillations necessary for radio communications? because this would require a very high rotor speed.
High frequency oscillations are obtained, for example, using a transistor generator.

Self-oscillating systems

Typically, undamped forced oscillations are maintained in the circuit by the action of an external periodic voltage.
But other ways to obtain continuous oscillations are also possible.

For example, there is a system in which free electromagnetic oscillations can exist, with an energy source.
If the system itself regulates the flow of energy into the oscillatory circuit to compensate for energy losses on the resistor, then it may experience undamped oscillations.

Systems in which undamped oscillations are generated due to the supply of energy from a source within the system itself are called self-oscillating. Undamped oscillations that exist in a system without the influence of external periodic forces on it are called self-oscillations.

A transistor generator is an example of a self-oscillating system.
It consists of an oscillating circuit with a capacitor of capacitance C and an inductance coil L, an energy source and a transistor.

How to create undamped oscillations in a circuit?

To prevent electromagnetic oscillations in the circuit from fading, it is necessary to compensate for energy losses for each period.

You can replenish energy in the circuit by recharging the capacitor.
To do this, you must periodically connect the circuit to a constant voltage source.

The capacitor should be connected to the source only during those time intervals when the plate connected to the positive pole of the source is positively charged, and the plate connected to the negative pole is negatively charged.
Only in this case will the source recharge the capacitor, replenishing its energy.

If the switch is closed at a time when the plate connected to the positive pole of the source has a negative charge, and the plate connected to the negative pole has a positive charge, then the capacitor will be discharged through the source. The energy of the capacitor will decrease.

A constant voltage source constantly connected to a circuit capacitor cannot support continuous oscillations in it, just as a constant force cannot support mechanical oscillations.
During half the period, energy enters the circuit, and during the next half of the period it returns to the source.

Undamped oscillations will be established in the circuit only if the source is connected to the circuit during those time intervals when energy can be transferred to the capacitor.
To do this, it is necessary to ensure automatic operation of the key.
At high oscillation frequencies, the key must have reliable performance. A transistor is used as such an almost inertia-free switch.

A transistor consists of an emitter, base and collector.
The emitter and collector have the same major charge carriers, such as holes (p-type semiconductor).
The base has majority carriers of opposite sign, such as electrons (n-type semiconductor).

Operation of a transistor generator

The oscillatory circuit is connected in series with a voltage source and a transistor so that a positive potential is applied to the emitter and a negative potential to the collector.
In this case, the emitter-base transition (emitter junction) is direct, and the base-collector transition (collector junction) is reverse, and no current flows in the circuit.
This corresponds to an open key.

In order for a current to arise in the circuit circuit and recharge the circuit capacitor during oscillations, it is necessary to provide the base with a potential negative relative to the emitter, and during those time intervals when the upper plate of the capacitor is charged positively and the lower plate is negatively charged.
This corresponds to a closed key.

Here the feedback is inductive
A coil of inductance L CB is connected to the emitter junction, inductively coupled to the coil of inductance L of the circuit.
Oscillations in the circuit due to electromagnetic induction excite voltage fluctuations at the ends of the coil, and thereby at the emitter junction.
If the phase of the voltage oscillations at the emitter junction is selected correctly, then the “jokes” of current in the circuit circuit act on the circuit at the required time intervals, and the oscillations do not die out.
On the contrary, the amplitude of oscillations in the circuit increases until the energy losses in the circuit are exactly compensated by the supply of energy from the source.
This amplitude is greater, the higher the source voltage.
An increase in voltage leads to increased “jokes” of current that recharges the capacitor.

Transistor generators are widely used not only in many radio devices: radio receivers, transmitting radio stations, amplifiers, computers.

Basic elements of a self-oscillating system

Using the example of a transistor generator, we can highlight the main elements characteristic of many self-oscillating systems.

1. An energy source that maintains undamped oscillations (in a transistor generator this is a constant voltage source).

2. An oscillatory system is that part of a self-oscillating system in which oscillations occur directly (in a transistor-based generator this is an oscillatory circuit).

3. A device that regulates the supply of energy from the source to the oscillatory system - a valve (in the considered generator - a transistor).

4. A device that provides feedback with the help of which the oscillatory system controls the valve (in a transistor generator - inductive coupling of a circuit coil with a coil in the emitter-base circuit).

Examples of self-oscillating systems

Self-oscillations in mechanical systems: a clock with a pendulum or a balancer (a wheel with a spring that performs torsional vibrations). The source of energy in a watch is the potential energy of a raised weight or a compressed spring.

Self-oscillating systems include an electric bell with a breaker, a whistle, organ pipes and much more. Our heart and lungs can also be considered as self-oscillating systems.