Polar and non-polar capacitors - what is the difference. What kind of device is a capacitor? Capacitor charge

An electric capacitor is one of the most common radio elements; it serves to store electricity (charge). The simplest capacitor can be imagined as two metal plates (plates) and a dielectric that is located between them.

When a voltage source is connected to a capacitor, opposite charges appear on its plates (plates) and an electric field appears, attracting them to each other, and even after the power source is turned off, such a charge remains for some time and the energy is stored in the electric field between the plates.

In electronic circuits, the role of a capacitor can also consist not only in accumulating charge but also in separating the direct and alternating current components, filtering pulsating current and various other tasks.
Depending on the tasks and operating factors, capacitors are used in very different types and designs. Here we will look at the most popular types of capacitors.

Aluminum electrolytic capacitors

Ceramic single layer capacitors

Ceramic multilayer capacitors

For example K10-17A or K10-17B.
Unlike those described above, they already consist of several layers of metal plates and a dielectric in the form of ceramics, which allows them to have a higher capacity than single-layer ones and can be of the order of several microfarads, but the maximum voltage for this type is still limited to 50 volts.
They are mainly used as filter elements and can work properly with both direct and alternating and pulsating current.

Ceramic high voltage capacitors

Tantalum capacitors

A solid tantalum capacitor has four main parts: anode, dielectric, electrolyte (solid or liquid), and cathode.
In terms of operating properties, tantalum capacitors are similar to electrolytic capacitors, but the maximum operating voltage is limited to 100 volts, and the capacitance usually does not exceed 1000 μF.
But unlike electrolytic ones, this type has much lower self-inductance, which makes it possible to use them at high frequencies, up to several hundred kilohertz.

Polyester capacitors

Polypropylene capacitors

The advantage of these capacitors is not only the high voltage, but also the extremely low loss tangent, since tg? may not exceed 0.001, which allows the use of capacitors at high frequencies of several hundred kilohertz and their use in induction heaters and launchers of asynchronous electric motors.

Starting capacitors (CBB-60) can have a capacity of up to 1000 µF, which becomes possible due to the design features of this type of capacitor. A metallized polypropylene film is wound onto a plastic core, and the entire roll is covered with a compound on top.

Capacitors

Capacitor – one of the most common radioelements. The role of a capacitor in an electronic circuit is to store electrical charge, separate DC and AC current components, filter ripple current, and much more.

Structurally, the capacitor consists of two conductive plates insulated with a dielectric. Depending on the design and purpose of the capacitor, the dielectric can be air, paper, ceramics, or mica.

The main parameters of capacitors are:

Nominal capacity. Capacity is measured in Faradah (F). The capacity of 1 Farad is very large. For example, the globe has a capacity of less than 1 F, or more precisely about 710 microfarads. True, here you need to understand that physicists love analogies. When talking about the electrical capacity of the globe, they mean that as an example they take a metal ball the size of planet Earth and which is a solitary conductor. This is just an analogy. In technology, there is an electronic component that has a capacity of more than 1 Farad - this is an ionistor.

Basically, in electronics and radio engineering, capacitors with a capacity equal to a millionth of a farad are used - microfarad ( 1uF = 0.000001 F ). Capacitors with capacities in the tens to hundreds of nanofarads are also used ( 1nF = 0.000000001 F ) and picofarads (1pF = 0.000000000001 F). The nominal capacity is indicated on the capacitor body.

In order not to get confused in the abbreviations (μF, nF, pF), and learn how to convert microfarads to picofarads, and nanofarads to microfarads, you need to know about the abbreviated notation of numerical quantities.

Rated voltage. This is the voltage at which the capacitor performs its functions. If the permissible value is exceeded, the capacitor will be broken, that is, it will turn into an ordinary conductor. The range of permissible operating voltages of capacitors ranges from several volts to several kilovolts ( 1 kilovolt – 1,000 volts ). The rated voltage is marked on the capacitor body.

The capacitor is depicted on the circuit diagrams as shown in the figure.

In addition to conventional ones, there are also electrolytic capacitors. Their capacity is much larger than that of conventional ones, therefore, the dimensions are also significantly larger. A distinctive feature of electrolytic capacitors is polarity. If ordinary capacitors can be soldered into a circuit without worrying about the polarity of the voltage applied to the capacitor, then an electrolytic capacitor must be included in the circuit strictly in accordance with the polarity of the voltage. Electrolytic capacitors have one terminal positive and the other negative.

Designation of an electrolytic capacitor on the diagrams.

Also widely used tuning capacitors. Trimmer capacitors are necessary in cases where precise adjustment of the capacitance in an electronic circuit is required. In such capacitors, the capacitance is adjusted once or very rarely.

It is designated as follows.

Along with tuning capacitors, there are also capacitors variable capacity . Unlike tuning capacitors, variable capacitors are used for frequent adjustment of the capacitance. In a simple (non-digital) receiver, tuning to a radio station is done using a variable capacitor.

Capacitor Properties

• Capacitor does not pass direct current and is an insulator for him.

  For alternating current, a capacitor is not an obstacle. The capacitor's resistance (capacitance) to alternating current decreases with increasing its capacitance and current frequency, and vice versa, increases with decreasing its capacitance and current frequency.

The property of a capacitor to provide different resistance to alternating current has found wide application. Capacitors are used for filtering, separating some frequencies from others, separating the variable component from the constant...

This is what constant capacitors look like.



Electrolytic capacitor. The long output is positive, the short one is negative.



Planar electrolytic capacitor. Indicated on the body rated capacity – 22 µF (22), rated voltage – 16 Volt (16V). It can be seen that the capacity is indicated only by numbers. The capacity of electrolytic capacitors is indicated in microfarads.



On the side of the negative terminal of the capacitor, there is a black semicircle on the top of the case.

A capacitor is a device that can store electrical charges. The simplest capacitor is two metal plates (electrodes) separated by some kind of dielectric. Capacitor 2 can be charged by connecting its electrodes to source 1 of direct current electrical energy (Fig. 181, a).

When a capacitor is charged, free electrons present on one of its electrodes rush to the positive pole of the source, as a result of which this electrode becomes positively charged. Electrons from the negative pole of the source flow to the second electrode and create an excess of electrons on it, so it becomes negatively charged. As a result of the flow of charging current i3, equal but opposite charges are formed on both electrodes of the capacitor and an electric field arises between them, creating a certain potential difference between the electrodes of the capacitor. When this potential difference becomes equal to the voltage of the current source, the movement of electrons in the capacitor circuit, i.e., the passage of current i3 through it stops. This moment corresponds to the end of the capacitor charging process.

When disconnected from the source (Fig. 181, b), the capacitor is capable of storing accumulated electrical charges for a long time. A charged capacitor is a source of electrical energy that has a certain e.g. d.s. es. If you connect the electrodes of a charged capacitor with some kind of conductor (Fig. 181, c), the capacitor will begin to discharge. In this case, the capacitor discharge current iр will flow through the circuit. The potential difference between the electrodes will also begin to decrease, i.e. the capacitor will transfer the accumulated electrical energy to the external circuit. At the moment when the number of free electrons on each electrode of the capacitor becomes the same, the electric field between the electrodes will disappear and the current will become zero. This means that the capacitor has completely discharged, i.e. it has released the electrical energy it had accumulated.

Capacitor capacity. The ability of a capacitor to accumulate and hold electrical charges is characterized by its capacitance. The greater the capacitance of the capacitor, the greater the charge accumulated by it, just as with an increase in the capacity of a vessel or gas cylinder, the volume of liquid or gas in it increases.

The capacitance C of a capacitor is defined as the ratio of the charge q accumulated in the capacitor to the potential difference between its electrodes (applied voltage) U:

C=q/U (69)

The capacitance of a capacitor is measured in farads (F). A capacitor has a capacity of 1 F, which, when charged,

in 1 C, the potential difference increases by 1 V. In practice, smaller units are predominantly used: microfarad (1 μF = 10 -6 F), picofarad (1 pF = 10 -12 μF).

The capacitance of a capacitor depends on the shape and size of its electrodes, their relative position and the properties of the dielectric separating the electrodes. There are flat capacitors, the electrodes of which are flat parallel plates (Fig. 182, a), and cylindrical ones (Fig. 182, b).

Not only devices specially manufactured at the factory have the properties of a capacitor, but also any two conductors separated by a dielectric. Their capacity has a significant impact on the operation of electrical installations with alternating current. For example, capacitors with a certain capacitance are two electrical wires, a wire and ground (Fig. 183, a), conductors of an electric cable, conductors and the metal sheath of the cable (Fig. 183,6).

The design of capacitors and their use in technology. Depending on the dielectric used, capacitors can be paper, mica, or air (Fig. 184). Using mica, paper, ceramics and other materials with high dielectric constant as a dielectric instead of air, it is possible to increase its capacity several times with the same dimensions of the capacitor. In order to increase the area of ​​the capacitor electrodes, it is usually made multilayer.

In AC electrical installations, power capacitors are usually used. In them, the electrodes are long strips of aluminum, lead or copper foil, separated by several layers of special (capacitor) paper impregnated with petroleum oils or synthetic impregnating liquids. Tapes of foil 2 and paper 1 are wound into rolls (Fig. 185), dried, impregnated with paraffin and placed in the form of one or several sections in a metal or cardboard case. The required operating voltage of the capacitor is provided by serial, parallel or series-parallel connections of individual sections.

Any capacitor is characterized not only by the value of its capacitance, but also by the value of the voltage that its dielectric can withstand. When the voltage is too high, the electrons of the dielectric are separated from the atoms, the dielectric begins to conduct current and the metal electrodes of the capacitor are short-circuited (the capacitor breaks down). The voltage at which this occurs is called breakdown voltage. The voltage at which the capacitor can operate reliably indefinitely is called operating voltage. It is several times less than the penetrating one.

Capacitors are widely used in power supply systems of industrial enterprises and electrified railways to improve the use of electrical energy with alternating current. On e. p.s. and diesel locomotives, capacitors are used to smooth out the pulsating current received from rectifiers and pulse interrupters, to combat sparking of contacts of electrical devices and radio interference, in control systems for semiconductor converters, as well as to create

reducing the symmetrical three-phase voltage required to power the electric motors of auxiliary machines. In radio engineering, capacitors are used to create high-frequency electromagnetic oscillations, separate electrical circuits of direct and alternating current, etc.

Electrolytic capacitors are often installed in DC circuits. They are made from two thin aluminum tapes 3 and 5 rolled into a roll (Fig. 185, b), between which paper 4 is placed, impregnated with a special electrolyte (a solution of boric acid with ammonia in glycerin). Aluminum tape 3 is coated with a thin film of aluminum oxide; this film forms a dielectric with a high dielectric constant. The electrodes of the capacitor are tape 3, coated with an oxide film, and an electrolyte; the second tape 5 is intended only to create electrical contact with the electrolyte. The capacitor is placed in a cylindrical aluminum housing.

When connecting an electrolytic capacitor to a DC circuit, the polarity of its poles must be strictly observed; the electrode coated with an oxide film must be connected to the positive pole of the current source. If switched on incorrectly, the dielectric breaks through. For this reason, electrolytic capacitors should not be connected to AC circuits. They also cannot be used in devices operating at high voltages, since the oxide film has a relatively low electrical strength.

Variable capacitors are also used in radio devices (Fig. 186). Such a capacitor consists of two groups of plates: fixed 2 and movable 3, separated by air gaps. Movable plates can move relative to fixed ones; When axis 1 of the capacitor is rotated, the area of ​​mutual overlap of the plates changes, and therefore the capacitance of the capacitor.

Methods for connecting capacitors. Capacitors can be connected in series or in parallel. With sequential

connection of several (for example, three) capacitors (Fig. 187, a) equivalent capacity

1 /C eq = 1 /C 1 + 1 /C 2 + 1 /C 3

equivalent capacitance

X C eq = X C 1 + X C 2 + X C 3

resulting capacitance

C eq = C 1 + C 2 + C 3

When capacitors are connected in parallel (Fig. 187b), their resulting capacitance

1 /X C eq = 1 /X C 1 + 1 /X C 2 + 1 /X C 3

Switching DC circuits on and off with a capacitor. When the R-C circuit is connected to a direct current source and when a capacitor is discharged to a resistor, a transient process also occurs with an aperiodic change in current i and voltage u c When the R-C circuit is connected to a direct current source with switch B1 (Fig. 188, a), the capacitor is charged. At the initial moment, charging current I start = U / R. But as charges accumulate on the electrodes of the capacitor, its voltage and c will increase, and the current will decrease (Fig. 188,b). If the resistance R is small, then at the initial moment of connecting the capacitor, a large current surge occurs, significantly exceeding the rated current of this circuit. When the capacitor is discharged onto resistor R (switch B1 opens in Fig. 189, a), the voltage across the capacitor u c and current i gradually decrease to zero (Fig. 189, b).

The rate of change of current i and voltage i during the transient process is separated by a time constant

The higher R and C, the slower the capacitor charges.

The processes of charging and discharging a capacitor are widely used in electronics and automation. With their help, periodic non-sinusoidal oscillations are obtained, called relaxation, and, in particular, the sawtooth voltage required for the operation of thyristor control systems, oscilloscopes and other devices. To obtain a sawtooth voltage (Fig. 190), periodically connect the capacitor to the power source, and then to the discharge resistor. The periods T 1 and T 2, corresponding to the charge and discharge of the capacitor, are determined by the time constants of the charge circuits T 3 and discharge T p, i.e., the resistances of the resistors included in these circuits.

A capacitor is a common two-pole device used in various electrical circuits. It has a constant or variable capacity and is characterized by low conductivity; it is capable of accumulating a charge of electric current and transmitting it to other elements in the electrical circuit.
The simplest examples consist of two plate electrodes separated by a dielectric and accumulating opposite charges. In practical conditions, we use capacitors with a large number of plates separated by a dielectric.

The capacitor starts charging when the electronic device is connected to the network. When the device is connected, there is a lot of free space on the electrodes of the capacitor, so the electric current entering the circuit is of the greatest magnitude. As it is filled, the electric current will decrease and disappear completely when the device’s capacity is completely filled.

In the process of receiving an electric current charge, electrons (particles with a negative charge) are collected on one plate, and ions (particles with a positive charge) are collected on the other. The separator between positively and negatively charged particles is a dielectric, which can be used in various materials.

When an electrical device is connected to a power source, the voltage in the electrical circuit is zero. As the containers are filled, the voltage in the circuit increases and reaches a value equal to the level at the current source.

When the electrical circuit is disconnected from the power source and a load is connected, the capacitor stops receiving charge and transfers the accumulated current to other elements. The load forms a circuit between its plates, so when the power is turned off, positively charged particles will begin to move towards the ions.

The initial current in the circuit when a load is connected will be equal to the voltage across the negatively charged particles divided by the value of the load resistance. In the absence of power, the capacitor will begin to lose charge and as the charge in the capacitors decreases, the voltage level and current in the circuit will decrease. This process will only complete when there is no charge left in the device.

The figure above shows the design of a paper capacitor:
a) winding the section;
b) the device itself.
In this picture:

1. Paper;
2. Foil;
3. Glass insulator;
4. Lid;
5. Frame;
6. Cardboard gasket;
7. Wrapping paper;
8. Sections.

Capacitor capacity is considered its most important characteristic; the time it takes to fully charge the device when connecting the device to a source of electric current directly depends on it. The discharge time of the device also depends on the capacity, as well as on the size of the load. The higher the resistance R, the faster the capacitor will empty.

As an example of the operation of a capacitor, consider the operation of an analog transmitter or radio receiver. When the device is connected to the network, the capacitors connected to the inductor will begin to accumulate charge, electrodes will collect on some plates, and ions on others. After the capacity is fully charged, the device will begin to discharge. A complete loss of charge will lead to the start of charging, but in the opposite direction, that is, the plates that had a positive charge this time will receive a negative charge and vice versa.

Purpose and use of capacitors

Currently, they are used in almost all radio engineering and various electronic circuits.
In an alternating current circuit they can act as capacitance. For example, when you connect a capacitor and a light bulb to a battery (direct current), the light bulb will not light. If you connect such a circuit to an alternating current source, the light bulb will glow, and the intensity of the light will directly depend on the value of the capacitance of the capacitor used. Thanks to these features, they are now widely used in circuits as filters that suppress high-frequency and low-frequency interference.

Capacitors are also used in various electromagnetic accelerators, photo flashes and lasers due to their ability to store a large electrical charge and quickly transfer it to other low-resistance network elements, thereby creating a powerful pulse.

In secondary power supplies they are used to smooth out ripples during voltage rectification.

The ability to retain a charge for a long time makes it possible to use them for storing information.

Using a resistor or current generator in a circuit with a capacitor allows you to increase the charging and discharging time of the device’s capacitance, so these circuits can be used to create timing circuits that do not have high requirements for temporal stability.

In various electrical equipment and in higher harmonic filters, this element is used to compensate reactive power.

TO category:

Production of radio equipment

Fixed capacitors

Fixed capacitors are used in various circuits to separate the alternating and direct current components and smooth out the ripple of rectifier voltages. In combination with other circuit elements, capacitors form resonant circuits widely used in radio equipment.

Fixed capacitors are classified according to their rated capacitance, accuracy class, rated operating voltage, purpose, dielectric material and design features.

The nominal values ​​of capacitor capacities are established by GOST 2519 - 60.

When manufacturing capacitors, the actual capacitance value differs from the nominal value indicated in the marking. The permissible deviation of the capacitance from the nominal value is called tolerance. According to this principle, all capacitors are divided into five classes: 0, 1, II, III, IV, their tolerances are respectively ±2%; ±5%; ±10%; ±20% and from - 20 to + 50%.

Depending on the purpose, there are loop, separating, blocking and filter capacitors.

Based on the dielectric material, capacitors are divided into mica, ceramic, paper, metal-paper, paper-oil, film, glass-enamel, glass-ceramic, electrolytic, air, vacuum, gas-filled.

Based on their design, capacitors are divided into tubular, disk, barrel, pot, crimped and sealed, flat and cylindrical, etc.

Regardless of the type, the capacitor is characterized by its operating voltage. The operating voltage is the voltage under which the capacitor plates can remain for a long time without breakdown of the dielectric separating them. Operating voltage is expressed in volts.

Of great importance for the normal operation of the capacitor is the resistance of its insulation. When the insulation resistance is low, leaks occur that disrupt the normal operation of the circuit. Losses in a capacitor are characterized by the dielectric loss tangent, which expresses the ratio of the power of active losses to the reactive power of the capacitor.

In low-power capacitors, energy losses are mainly caused by dielectric conductivity and dielectric hysteresis, i.e., losses due to rotation of polar molecules in the direction of the field when voltage is applied to the plates. Losses in the plates and leads are small, so they are usually neglected.

One of the most important characteristics of a capacitor is stability - the constant value of the capacitor's capacitance during operation. The change in capacity can be either temporary or irreversible. The main factor influencing the stability of the capacitor capacity is the effect of ambient temperature and heating of the capacitor due to the power dissipated on it. As the temperature rises, the geometric dimensions of the material increase, which entails a temporary (until the temperature returns to its original value) change in capacity.

However, an increase in temperature can also lead to irreversible changes in capacity. For example, in a capacitor, a rearrangement of the air gaps between the plates and the dielectric may occur. An irreversible change in capacitance also occurs due to the aging of the dielectric, which consists of a change in its dielectric constant.

Measures to combat changes in the capacitance of capacitors are impregnation of them with special compounds (castor oil, ceresin, petroleum jelly, etc.) and silvering of mica plates instead of using metal foil. In especially critical cases, capacitors are sealed.

When marking capacitors, indicate the type, rated operating voltage, rated capacitance (in picofarads or microfarads), accuracy class (permissible deviation from the rated capacitance in percent).

Mica and glass-enamel capacitors have additional indications of belonging to the TKE group (temperature coefficient of capacitance) in the form of the letters A, B, C, D for mica and P, O, M, P for glass-enamel. The temperature coefficient of capacitance of ceramic capacitors is indicated by a color code: capacitor bodies are painted in the colors of the TKE group.

Rice. 1. Mica capacitors: a -KSO; b – KSG

KSO capacitors can operate in the temperature range from 60 to 4 70 ° C, at a relative air humidity of up to 80% (short-term - up to 98%) and at an atmospheric pressure of at least 5 mm Hg. cm (for capacitors for operating voltages up to 500 V). When installing KSO capacitors in the circuits of various types of equipment, it should be remembered that they have different TKE.

In addition, temperature-resistant molded mica capacitors KSOT are produced, as well as high-reliability capacitors K31U-ZE.

In addition to molded capacitors, sealed mica capacitors in metal and ceramic cases are produced.

KSG capacitors (sealed mica capacitors) in metal cases (Fig. 39, b) come in two types: KSG-1 and KSG-2. Capacitors KSG -1 are used for nominal capacities of 470 - 20,000 pF, and KSG -2 - from 0.02 to 0.1 μF at an operating voltage of 500 and 1000 V. These capacitors are available in 0, I, II and III accuracy classes.

SGM capacitors (sealed mica small-sized) in moisture-proof ceramic cases, soldered at the ends, have silver linings deposited on mica. They are produced in four types of overall dimensions: SGM -1, SGM -2, SGM -3 and SGM -4. The weight of SGM capacitors is from 3 to 10 g, nominal capacitance values ​​are from 100 to 10 000 pf with tolerances for 0 I, II and III accuracy classes. They are designed for operating voltages from 250 to 1500 V. In a humid atmosphere, these capacitors operate more stably than KSO capacitors.

For the manufacture of mica capacitors, the highest grade mica is used - muscovite. The capacitor plates are made of thin metal foil (aluminum, lead-tin or copper) with a thickness of 7 - 100 microns.

Silver is used as the plates of highly stable capacitors, which is burned in or sprayed.

Ceramic capacitors. Ceramic capacitors are divided according to their design into tubular and disk. More common are tubular capacitors KTK and KT (tubular ceramic capacitors). The KTK capacitor (Fig. 40, a) is a thin-walled ceramic tube, the outer and inner surfaces of which are coated with thin layers of silver. The terminals from the plates are made of silver-plated copper wire.

KTM capacitors (small tubular capacitors) have a design similar to KTK capacitors, but their dimensions are smaller.

The so-called support ceramic capacitors KO are very convenient for installation. In them, the outer lining is connected to a bolt, which serves both to strengthen the capacitor on a metal chassis (panel) and to reliably ground this lining. The inner lining has a petal-shaped outlet.

In radio equipment intended to operate in high humidity, it is recommended to use KGK tubular capacitors (sealed ceramic capacitors) having a moisture-proof ceramic shell.

The basis of the KDK and KD capacitors (ceramic disk capacitors) is narrowed by a ceramic plate made in the form of a disk. Its linings are thin layers of silver deposited on each of the surfaces of this plate. KDK capacitors (Fig. 2, c), depending on the diameter of the disk, are divided into three types:

Rice. 2. Ceramic capacitors: a - KTK; b-KGK : v-KDK

KDM capacitors (small disk capacitors), intended for small-sized equipment assembled on semiconductor devices, have a diameter of 4 mm. The terminals of the KDK and KDM are wires soldered to the plates.

KDU capacitors (disc capacitors for ultra-short wave circuits) have the same diameter as the KDK, but their conclusions are made in the form of short wide petals.

In KDO capacitors (disc support capacitors), one of the plates is soldered to the head of the bolt, which serves to secure the capacitor to the chassis and securely connect this plate to the chassis. The second plate has a petal-shaped output.

Rice. 3. Paper capacitor section: 1 - capacitor paper: 2 - foil

As a dielectric in ceramic capacitors, special capacitor ceramics are used, characterized by a relatively high dielectric constant and low losses. KTK capacitors are produced with capacities from 2 to 100 pF, and KDK capacitors are produced from 1 to 75 pF in 0, I, II and III accuracy classes. KDM capacitors are manufactured with nominal capacities from 1 to 220 pF according to accuracy classes I, II and III, and KTM capacitors with a capacity from 1 to 10,000 pf also according to accuracy classes I, II and III.

Recently, ceramic capacitors with large capacitance values ​​(about 0.01 μF) with small dimensions of CLS (ceramic cast sectioned), KP (ceramic plate) and KPS (ceramic plate ferroelectric) have found widespread use in radio equipment based on semiconductor devices.

Paper capacitors. In paper capacitors, capacitor paper with a thickness of 4 to 10 microns is used as a dielectric, and aluminum or lead-tin foil with a thickness of 7-7.5 microns is used as plates.

The paper capacitor section consists of metal foil strips 2, between which capacitor paper / is laid; the number of layers of paper must be at least two. With one layer of paper, the probability of rapid breakdown of the capacitor will greatly increase, since the paper contains a certain amount of electrically conductive inclusions.

In the production of radio equipment, KBG capacitors (sealed paper capacitors) are mainly used. This type of capacitor has a number of varieties:
— KBG-I - in a cylindrical case made of ceramics or glass;
— KBG-M1 and KBG-M2 - in a metal case with one or more terminals isolated from the case (Fig. 42, b); KBG-MP - in a metal rectangular case, flat;
— KBG -MN-in a metal rectangular case, normal.

Nominal capacitance values ​​of capacitors KBG-I, KBG-MN, KBG-MP from 470 pf to 10 µf at operating voltages of 200, 400, 600, 1000 and 1500 V, and capacitors KBG-M1 and KBG-M2 from 0.1 to 0 .25 µF at operating voltages of 200, 400 or 600 V.

For small-sized equipment based on semiconductor devices, special capacitors BM, BGM (sealed small-sized paper - Fig. 42, e) and BGMT (sealed small-sized heat-resistant paper capacitors) are produced.

Nominal capacitances of BM capacitors: from 510 to 2200 pF at an operating voltage of 300 V; from 3300 pF to 0.03 µF at an operating voltage of 200 V; 0.04 and 0.05 µF at an operating voltage of 150 V. These capacitors are manufactured according to accuracy classes II and III.

BGM capacitors (BGM -1 and BGM -2) are produced with operating directivity, it should be noted small-sized sealed capacitors K40P-1, sealed K40P-2, non-sealed K40P-3, as well as heat-resistant K40U-9 (up to + 125 ° C) .

Rice. 4. Paper capacitors: a - KBG-I; b - CBG-M; c -CBG-MP; g - CBG-MN; 3 -BGM; e - BM

The manufacturing technology of paper capacitors includes winding sections, pressing, drying, impregnation and assembly.

Metal paper capacitors. Metal-paper capacitors are widely used because they have relatively small dimensions (small volume and weight per unit of capacity) and at the same time have good insulating properties. The plates of the metal-paper capacitor are made in the form of a metal layer up to hundredths of a micron thick. The metal is applied to the paper tape by evaporation under vacuum.

Metal paper capacitors are produced in sealed metal cases of rectangular or cylindrical shape. They are marked MBGP (sealed metal paper in a rectangular housing), MBGC (sealed metal paper in a cylindrical housing), MB GO (sealed metal paper, one layer of dielectric), MBGCh (sealed metal paper frequency), MB G (sealed metal paper heat-resistant).

Depending on the purpose, these capacitors are manufactured with a capacity of 0.025 to 30 μF for operating voltages from 160 to 1500 V. .MBM (small-sized metal paper) capacitors for an operating voltage of 160 V are intended for use in equipment using semiconductor devices. Some types of metal-paper capacitors are shown in Fig. 5.

Zinc, aluminum and nickel are usually used as the metal coating of metal-paper capacitors. Since the metal layer applied to the paper is very thin and prone to oxidation, the shelf life of metallized paper in the open air is limited. Coatings made of aluminum and nickel are less susceptible to corrosion compared to zinc.

Metal-paper capacitors self-heal after electrical breakdown. Self-healing occurs due to the fact that the electrical energy stored in the capacitor or supplied to it from the outside is sufficient to evaporate the metal layer at the site of the breakdown and thereby isolate the damaged area from the rest of the metal coating. Capacitors with zinc coating have the best self-healing properties.

The self-healing effect makes it possible to produce metal-paper capacitors with a single layer of dielectric, in contrast to capacitors with foil plates.

Metal-paper capacitors, like ordinary paper ones, are subjected to impregnation, which is preceded by thorough vacuum drying.

Film capacitors. Organic high-molecular films are used as a dielectric in capacitors of this group. Some types of film capacitors are shown in 6. In their production, polystyrene and fluoroplastic films are most widely used. Polystyrene is a non-polar dielectric and is therefore widely used for the production of capacitors operating in both low- and high-frequency circuits.

Rice. 5. Metal-paper capacitors: a - MBGP; b - MBGC; c -MBGO; g -MBGT

Polystyrene capacitors are characterized by a small dielectric loss tangent in a wide frequency range, a relatively low temperature coefficient of capacitance (-150-10-6 per GS) and high insulation resistance. A significant disadvantage of polystyrene capacitors. is their low heat resistance (maximum operating temperature 60-70 ° C).

Capacitors where fluoroplastic-4 serves as a dielectric have high heat resistance. These capacitors can operate for a long time at temperatures up to 200 and even 250 ° C under short-term load. Fluoroplast-4 is non-polar. Polar organic dielectrics include fluoroplastic-3. Capacitors in which fluoroplastic-3 serves as a dielectric are used only in low-frequency or direct current circuits due to the increased value of the dielectric loss tangent.

Sections of polystyrene film capacitors are manufactured on conventional winding machines used in the production of paper capacitors. Aluminum foil is used as plates in polystyrene film capacitors. Film thickness 15-20 microns\ foil thickness 7.5 microns.

To reduce the size of capacitors, metallized polystyrene film is used, while the reliability of the capacitor is maintained, and the overall dimensions are reduced by 5-6 times compared to capacitors with aluminum foil linings.

Rice. 6. Film capacitors: O-PGT; b-PM; e-PSO; g-FGTI

Zinc is used as the base metal for the linings, which is deposited on a thin layer of tin. These capacitors are called metal film capacitors. Metal film capacitors are enclosed in rectangular metal cases with ceramic insulators or in tubular aluminum cases filled with epoxy resin at the ends.

For the manufacture of capacitors from fluoroplastic-4, a film with a thickness of 5 to 40 microns is used. The linings in them are aluminum foil with a thickness of 7.5 microns. Fluoroplastic capacitors are divided into two groups: low-voltage, the cylindrical case of which is made of aluminum and has caps made of fluoroplastic-4 on the end sides, secured by rolling the edges of the case, and high-voltage - in ceramic cylindrical cases, on both sides of the case of which Invar caps are welded, which Provides vacuum sealing. High voltage housing

The condenser is filled under pressure with nitrogen to prevent possible electrical breakdown between the edges of the plates and ionization of the gas.

The industry produces polystyrene film capacitors PO (open) and PM (small-sized) and fluoroplastic capacitors FT (heat resistant up to +200 °C) for low voltage radio equipment (no more than 1 kV). Of the new types of film capacitors, we can note the capacitors K72P-6 (heat-resistant, up to +200 ° C), K73P-2 (metal film) and K76P-1 (varnish film).

Electrolytic capacitors. Electrolytic capacitors are divided into high-voltage with an operating voltage of 250-450 V (capacity of several hundred microfarads), used mainly in smoothing filters of rectifiers and decoupling filters, in the anode circuits of screen grids, and low-voltage with an operating voltage of 6-60 V (capacity of up to several thousand microfarads) used in semiconductor technology.

The first group includes EC capacitors (electrolytic capacitors), manufactured with nominal capacities from 5 to 2000 μF and operating voltage from 8 to 500 V. By design, they come in three types: KE-1, KE-2 and KE-3.

This group also includes EGC capacitors (electrolytic sealed cylindrical capacitors) with a capacity of 5 to 50 microfarads for operating voltages from 6 to 500 V.

The second group includes EM (electrolytic small-sized) and EMI (electrolytic miniature) capacitors. They are designed to operate in direct and pulsating current circuits of small-sized transistor units. Rated DC voltage 3 V of EMI capacitors and from 4 to 150 V of EM capacitors, nominal capacitance 0.5; 1.25 and 10 µF for EMI and from 0.5 to 50 µF for EM. Permissible deviations of the actual capacitance value from the nominal value: from +80 to -20% for capacitors with a capacity of 0.5 μF, from + 200 to -10% for capacitors with a capacity of 1.25 and 10 μF. The operating temperature range is from -20 to +50° C with a relative air humidity of no more than 98% and an atmospheric pressure of 720-780 mm Hg. Art.

Among the new types of small-sized aluminum electrolytic capacitors, the industry produces capacitors K50-3 for operating voltages from 6 to 450 V, K50-ZI (pulse), K50-6 (non-polar), etc.

In Fig. Figure 7 shows the types of some electrolytic capacitors, in which the dielectric is an oxide film formed on aluminum foil, which acts as the first plate (anode) of the capacitor, the second plate is the electrolyte in contact with the oxide film. The second foil tape (cathode) serves as a current conductor to the electrolyte.

The oxide film has a thickness of 0.01-1.5 microns and has unipolar (one-sided) conductivity, so electrolytic capacitors can only operate in DC or pulsating current circuits.

According to the design and manufacturing method, electrolytic capacitors are liquid (wet), the oxidized aluminum anode of which is located in a liquid or semi-liquid electrolyte, and dry, obtained by winding strips of aluminum foil (oxidized anode and non-oxidized cathode) and separated by a fibrous spacer impregnated paste or semi-liquid electrolyte.

Dry electrolytic capacitors are the most widely used. For the anodes of these capacitors, a material containing from 99.8 to 99.99% aluminum and a minimal amount of iron is used.

Aluminum anode foil used in electrolytic capacitors has a thickness of 50-150 microns.

Less stringent requirements apply to aluminum used for the manufacture of cathodes; it contains up to 0.4% impurities. The thickness of the cathode foil is 7.5-16 microns.

In dry electrolytic capacitors, special types of paper and cotton fabric impregnated with electrolytes are used for laying between aluminum strips.

Recently, the industry has widely produced electrolytic capacitors with a dielectric made of tantalum oxide film, which, compared to aluminum, has a higher dielectric constant.

Rice. 7. Electrolytic capacitors: a - KE 3; b -KE-1-OM; c -KE-2M; d - KEG -2; d - KEG -1M

Tantalum capacitors are significantly smaller in size, more reliable and have better electrical characteristics than capacitors based on aluminum oxide film. The capacitance n dielectric loss tangent of a dry tantalum capacitor changes slightly with temperature changes down to -60° C.

Liquid tantalum capacitors have a cylindrical anode made from pressed tantalum powder, heat-treated in a vacuum. Heat treatment is necessary to sinter tantalum powder grains. The resulting porous anode structure is characterized by a large active surface, which helps to increase the capacitance of the capacitor. This method increases the effective surface of the anode by 40-50 times compared to the sealed surface of the cylinder.

The dielectric in the capacitor is a thin film of tantalum oxide on the surface of the grains, and the role of the second plate is performed by an acid electrolyte.

In Fig. Figure 8 shows the device of a liquid electrolytic tantalum capacitor IT.

The capacitor ETO (electrolytic tantalum with a volumetric porous anode) has several varieties: ETO -1, ETO -2 and ETO -3,4. A modification of this type are capacitors K52-2 and K52-3.

From dry tantalum capacitors, ET (electrolytic tantalum) and ETN (non-polar) capacitors are produced.

A further design development of capacitors of this group are tantalum capacitors with solid electrolyte. The anode of such a capacitor is made in the form of a cylinder of porous sintered tantalum. A layer of dielectric (tantalum oxide) on the surface of compressed particles is obtained electrolytically. The role of the second plate in this capacitor is played by a layer of Manganese Dioxide, applied by the method of pyrolysis (decomposition) of manganese nitrate.

Rice. 8. Design of a liquid electrolytic tantalum capacitor ETO with a volumetric porous anode: I - output; 2 - textolite ring; 3 - taptal cover; 4 - rubber ring: 5 - electrolyte; 6 - anode; 7 - liner made of chemically resistant metal; 8 - steel body; 9 - cathode output; 10 - tan tal rod; 11-fluoroplastic ring

The temperature characteristic of a capacitor with a solid electrolyte compares favorably with that of liquid electrolytic tantalum capacitors, especially at subzero temperatures, when liquid electrolytes thicken or solidify. Losses in a capacitor with a solid electrolyte depend little on temperature and remain at the same level down to very low temperatures. In addition, when operating at high frequencies, the characteristics of the capacitors are also more favorable than those of liquid-type tantalum capacitors. Long-term storage of capacitors with a porous tantalum anode and solid electrolyte showed that their electrical characteristics practically do not change over time.

Glass enamel capacitors (Fig. 9). In capacitors of this group, the dielectric is thin layers of glass enamel, and the plates are silver films applied to the glass-enamel layers by burning. Approximate enamel composition: 15-25% Si02; 3-11% Na20 + K20; 15-25% PbO, the rest are oxides of other divalent metals.

Glass-enamel capacitors KS-1 and KS-2 have an operating temperature range from -60 to +100° C; insulation resistance of at least 20 000 Mom; the loss tangent at a temperature of +20±5°C is no more than 15-1Q-4, and at + 100±5°C is no more than 20-10-4, the temperature coefficient of the capacitance in the temperature range from +20 to 100°C is + (65±35)-10-6; permissible deviations ±2, ±5, ±10, ±20%.

Glass-enamel capacitors are used in radio equipment along with mica and ceramic ones.

The peculiarities of fastening the leads of KS capacitors to the body create some inconvenience when forming the leads, which often causes defects (soldering delamination). Therefore, KS capacitors must be handled with care during all operations, including adjustment.

Glass-enamel capacitors of constant capacity KS-1 are designed for operation in direct and alternating current circuits, as well as in pulsed circuits. Operating temperature range from -60 to +100 °C; relative humidity up to '98%, rated DC voltage 300 V. Temperature stability of the container is no more than 0.1%. Permissible deviations of actual container values ​​from nominal values: ±2% and ±5%.

Rice. 9. Glass enamel capacitor

Tuned capacitors. Trimmer capacitors (trimmers) are used to adjust high-frequency oscillatory circuits during the adjustment process. They are manufactured with an air or ceramic dielectric and ceramic bases are used to increase the stability of the capacitance.

Rice. 10. Trimmer capacitors: a - with air dielectric; b - with a ceramic dielectric; 1 - stator; 2 - rotor; 3 - conclusions; 4 - holes for fastening

Ceramic tuning capacitors KPK are designed for an operating voltage of 250 V and are mainly used for tuning high-frequency circuits in receivers.

KPK-1 capacitors have minimum capacitance values ​​of 2, 4, 6 and 8 pF and maximum values ​​of 7, 15, 25 and 30 pF, respectively.

Capacitors KPK-2 and KPK-3 have minimum capacitances of 6, 10 and 25 pF and maximum capacitances of 60, 100 and 150 pF.

For small-sized equipment, tuning capacitors KPK-MN (small-sized for wall-mounted installation) and KPK-MP (small-sized for printed circuit mounting) are produced.