Useful materials. Soviet paper capacitors

They are very widely used in electronic and radio engineering devices and instruments. They may vary in quantity and capacity in electronic circuits, but they are found almost everywhere. Such a widespread use of devices is explained by the fact that in circuits such devices can perform various functions and tasks.

First of all, capacitors are used in filters of various voltage stabilizers and rectifiers; in addition, they are used to transmit signals between cascades, operate high-frequency and low-frequency filters, and select the oscillation frequency and time delay intervals on different generators. To better understand the features and applications of such devices, you should analyze in detail the existing types and characteristics of capacitors.

Characteristics and parameters

Any user can obtain comprehensive information about the type and technical characteristics of the capacitor on the device case, where the manufacturer of the device and the date of its manufacture are also sometimes indicated.

The most important parameter of any capacitor is its rated capacity. The rules for designating capacity ratings are described in the current GOST standards. According to the provisions of GOST, the nominal capacity of capacitors up to 9999 pF is indicated on the diagrams without indicating the unit of measurement. The capacitance of devices with a nominal value of more than 9999 pF and up to 9999 μF is indicated on the diagrams with an indication of the unit of measurement. The next characteristic indicated on the device body is the permissible deviation from the nominal values.

The second most important value of a capacitor is its rated voltage. They can be designed to operate in networks with different voltages: from 5 to 1000 V or more. Experts recommend choosing devices with a margin of rated voltage. The use of low-rated devices can lead to dielectric breakdowns and failure of the devices.

The remaining parameters are considered additional and not always important, therefore, on the cases of some devices, the description may be limited to capacity and rated voltage. If additional technical characteristics are indicated, then the operating temperature of the device, operating rated current and other data can also be found on the case.

It should also be taken into account that capacitors on the market today can be three-phase or single-phase, intended for external or internal installation.

What types of capacitors are there?

There are different classifications of capacitors used in electronic circuits. Most often, such devices are divided into types according to the type of dielectric used in them. Based on the characteristics of the dielectric, the following types can be distinguished:

• with liquid dielectrics.
• vacuum, in which there is no dielectric.
• with a solid organic dielectric.
• with gas dielectric.
• electrolytic or oxide semiconductor with an electrolyte or oxide metal layer.
• with a solid inorganic dielectric.

The second classification option is based on the probability of fluctuations in the capacity value. Based on this characteristic, the following devices can be distinguished:

• Variables – which can change capacitance due to voltage or temperature conditions.
• Constant - the size of the capacity does not change throughout its service life.
• Trimmers - with variable capacity, used for periodic or one-time adjustment of circuits.

According to the scope of operation, all capacitors are divided into the following types:

• Low voltage, used in low voltage networks.
• High voltage, used in high voltage networks.
• Impulse – capable of releasing a short-term impulse.
• Starters - for starting the electric motor.
• Noise suppressing.

There are other classes based on areas of application, but in practice they are extremely rare.

The table below shows the most common capacitors and their designations in the diagrams.

Electrical capacitorsare a means of storing electricity in an electric field. Typical applications of electrical capacitors are smoothing filters in power supplies, interstage communication circuits in variable signal amplifiers, filtering noise that occurs on the power buses of electronic equipment, etc.

Electrical characteristics of the capacitor determined by its design and the properties of the materials used.

When choosing a capacitor for a particular device, the following circumstances must be taken into account:

a) the required capacitance value of the capacitor (uF, nF, pF),

b) operating voltage of the capacitor (the maximum voltage value at which the capacitor can operate for a long time without changing its parameters),

c) required accuracy (possible spread of capacitance values),

d) temperature coefficient of capacitance (dependence of capacitor capacitance on ambient temperature),

e) stability of the capacitor,

f) leakage current of the capacitor dielectric at rated voltage and given temperature. (The dielectric resistance of the capacitor may be indicated.)

In table 1 - 3 show the main characteristics of capacitors of various types.

Table 1. Characteristics of ceramic, electrolytic and metallized film capacitors

Table 2. Characteristics of mica capacitors and capacitors based on polyester and polypropylene

Table 3. Characteristics of mica capacitors based on polycarbonate, polystyrene and tantalum

Ceramic capacitors used in dividing circuits, electrolytic capacitors are also used in dividing circuits and anti-aliasing filters, and metallized film capacitors used in high-voltage power supplies.

Mica capacitors used in sound reproducing devices, filters and oscillators. Polyester based capacitors- these are general purpose capacitors, and polypropylene based capacitors used in high-voltage DC circuits.

Polycarbonate based capacitors used in filters, oscillators and timing circuits. Capacitors based on polystyrene and tantalum They are also used in timing and separating circuits. They are considered general purpose capacitors.

Some notes and tips on working with capacitors

You should always remember that the operating voltages of capacitors should be reduced as the ambient temperature increases, and to ensure high reliability it is necessary to create a large voltage reserve.

If the maximum constant operating voltage of the capacitor is specified, this refers to the maximum temperature (unless otherwise stated). Therefore, capacitors always operate with a certain margin of safety. Nevertheless it is necessary to ensure their actual operating voltage is at a level of 0.5-0.6 of the permitted value.

If a limit value for alternating voltage is specified for a capacitor, then this applies to a frequency of (50-60) Hz. For higher frequencies or in the case of pulsed signals, the operating voltages should be further reduced to avoid overheating of the devices due to dielectric losses.

Large capacitors with low leakage currents are able to retain the accumulated charge for quite a long time after the equipment is turned off. To ensure greater safety, a 1 MΩ (0.5 W) resistor should be connected to the discharge circuit in parallel with the capacitor.

In high-voltage circuits, capacitors are often connected in series. To equalize the voltages across them, you need to connect a resistor with a resistance of 220 k0m to 1 MOhm in parallel to each capacitor.

Rice. 1 Using resistors to equalize voltages on capacitors

Ceramic pass capacitors can operate at very high frequencies (over 30 MHz). They are installed directly on the device body or on a metal screen.

Non-polar electrolytic capacitors have a capacitance of 1 to 100 μF and are designed for 50 V. In addition, they are more expensive than conventional (polar) electrolytic capacitors.

When choosing a power supply filter capacitor, you should pay attention to the amplitude of the charging current pulse, which can significantly exceed the permissible value. For example, for a capacitor with a capacity of 10,000 μF, this amplitude does not exceed 5 A.

When using an electrolytic capacitor as an isolation capacitor, it is necessary to correctly determine the polarity of its connection. The leakage current of this capacitor can affect the mode of the amplifier stage.

In most applications, electrolytic capacitors are interchangeable. You just need to pay attention to the value of their operating voltage.

The terminal from the outer foil layer of polystyrene capacitors is often marked with a colored line. It must be connected to a common point in the circuit.

Rice. 2 Equivalent circuit of an electric capacitor at high frequency

Color coding of capacitors

On the body of most capacitors their rated capacity and operating voltage are written. However, there are also color markings.

Some capacitors are marked with two lines. The first line indicates their capacitance (pF or μF) and accuracy (K = 10%, M - 20%). The second line shows the permissible DC voltage and the dielectric material code.

Monolithic ceramic capacitors are marked with a three-digit code. The third digit shows how many zeros need to be added to the first two to get the capacitance in picofarads.

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Example. What does code 103 on a capacitor mean? Code 103 means that you need to add three zeros to the number 10, then you get the capacitance of the capacitor - 10,000 pF.

Example. The capacitor is labeled 0.22/20 250. This means that the capacitor has a capacitance of 0.22 µF ± 20% and is designed for a constant voltage of 250 V.

Content:

A capacitor is a device capable of storing electrical charges. It is used in electrical and electronic circuits everywhere. Modern industry produces many types of them, which differ from each other in different parameters. This is the capacity, principle of operation, type of separation of charging conductors, range of permissible voltages, layout, materials from which the device is made.

Any capacitor consists of two conductors separated by an insulator. Since charging a capacitor is the introduction of charged particles onto these conductors, one conductor of one sign and the other of another, and the charges will be held by the force of mutual attraction, the efficiency depends on this force. The closer the conductors are to each other and the larger their “almost touching” area, the larger it is. The medium separating the conductors also makes its contribution. This medium is a dielectric having a certain dielectric constant.

d – thickness of the dielectric separating the metal plates

The capacitance of the capacitor is calculated by the formula

Where S is the area of ​​the plates, d is the thickness of the dielectric (the distance between the plates), and ε is the permeability of the dielectric used relative to vacuum, the dielectric constant of which is known quite accurately:

Here it is expressed through other SI units. Here there are meters cubed in the denominator, and seconds to the fourth power in the numerator, which comes from the formula where the denominator is the speed of light squared. And then the capacitance C is measured in farads.

And from the formula it is clear that the capacitance depends precisely on the area of ​​the plates, the distance between them (which is filled with a dielectric) and the dielectric material, the value of ε of which can be found in the tables. Capacitors are classified according to type of use and type of component.

Classification by principle of action

The simplest capacitor is also called dry, or solid-state, because all its materials are solid and very ordinary. Knowing the description, it can be made manually. Paper tape is used as an insulator, but since it is hygroscopic, it is impregnated with paraffin or oil.

Dry capacitors

Dry or wet capacitors - depends on the filling between the plates. For dry ones, it can be paper, ceramics, mica, plastic (polyester, polypropylene). Each dielectric has its own physical properties. The most durable (ceramics) resist physical destruction and breakdown well. Plastic ones allow coatings to be applied in the form of metal spraying directly onto the dielectric layer, which allows one to follow the path of microminiaturization.

Types of capacitors with other component states

In addition to solid dielectric, there are capacitors with dielectric:

• liquid;

• gaseous (filled with inert gas to protect the electrodes);

• vacuum;

• air.

However, electrodes are not always completely solid.

Electrolytic capacitors

To create a large capacity, methods of bringing the plates together are used, not mechanical, but chemical. Taking advantage of the fact that aluminum foil is always covered in air with a layer of dielectric (Al 2 O 3), a liquid electrode in the form of an electrolyte is brought very close to the aluminum electrode. Then the thickness of the insulating gap is calculated in atomic distances, and this dramatically increases the capacitance.

d – dielectric thickness

Since there is a layer of oxide, a dielectric, on the lower surface of the upper plate, it is precisely its thickness that should be considered d - the thickness of the dielectric. The bottom electrode is the bottom plate, plus a layer of electrolyte with which the paper is impregnated.

In electrolytic capacitors, the charge is created not only by free electrons of the metal, but also by electrolyte ions. Therefore, the polarity of the connection is important.

In addition to electrolytic capacitors that use metal oxide as insulation, field-effect (MOS) transistors operate on the same principle. They are often used in electronic circuits as capacitors with a capacity of several tens of nanofarads.

Another similar operating principle is used by oxide-semiconductor capacitors, in which instead of a liquid electrolyte there is a solid semiconductor. But these types do not exhaust capacitors, the dielectric layer of which has a microscopic thickness.

Supercapacitor or ionistor

Another option is to create a layer that plays the role of a dielectric in a liquid electrolyte. If you pour it on the surface of a certain porous conductor (activated carbon), then if there is a charge on it, ions of the opposite sign from the electrolyte “stick” to the conductor. And they, in turn, are joined by other ions. And everything together forms a multilayer structure capable of accumulating electrical charges.

The processes in a liquid electrolyte of a special composition for supercapacitors already resemble something that happens in battery electrolytes. The ionistor's characteristics are similar to those of batteries; in addition, its charging is easier and faster. And in them, during charging/discharging cycles, there is no damage to the electrodes, as is usually the case in batteries. Ionistors are more reliable, durable, and they are used as power devices in electric vehicles. And the porous substance of the electrodes provides simply a colossal surface area. Together with the nanoscopically small thickness of the insulating layer in the electrolyte, this creates the gigantic capacity of supercapacitors (ultracapacitors) - farads, tens and hundreds of farads. There are many different supercapacitors available, some of which look no different from batteries.

Classification by application

Most capacitors are manufactured for use in debugged, tuned electrical circuits and circuits. But in many circuits, electrical or frequency parameters are adjusted. Capacitors are very convenient for this purpose: you can change the capacitance without changing the electrical contacts between the plates.

On this basis, capacitors are constant, variable and tuning.

Trimmers are usually designed in miniature form and are designed for permanent operation in circuits after a small preliminary optimizing adjustment. Variables have wider ranges of parameters to allow for systematic tuning (for example, searching for a wave in a radio receiver).

By voltage range

The operating voltage range is a very important characteristic of a capacitor. In electronic circuits, voltages are usually small. The upper limit is about 100 volts. But power supply circuits, various power supplies, rectifiers, device stabilizers require the installation of capacitors that could withstand voltages up to 400–500 volts - taking into account possible surges, and even up to 1000 volts.

But in electricity transmission networks the voltages are much higher. There are high-voltage capacitors of special design.

Using a capacitor outside its voltage range risks breakdown. After a breakdown, the device becomes simply a conductor and ceases to perform its functions. This is especially dangerous where a capacitor is installed to decouple circuits by current, separating the DC voltage from the AC component. In this case, a breakdown threatens that part of the circuit where constant voltage will then flow: other elements may burn, and there may be an electric shock. For electrolytic capacitors, this phenomenon also threatens an explosion.

Left – up to 35 kV, right – up to 4 kV

Since breakdown at high voltage requires a certain minimum distance between conductors, devices for high-voltage versions are usually made of significant size. Or they are made of certain breakdown-resistant materials: ceramic and... metal-paper. Of course, everything is in a housing that has the appropriate properties.

Capacitor markings

There are several markings. The old marking may consist of three or four digits, in which case the first two (three) digits indicate the mantissa of the capacitance (in picofarads), the last digit gives the power of the tens factor.

This is what the three-digit marking of capacitors looks like (designation of capacitances)

As you can see, this marking only covers the capacitance of capacitors.

Code marking contains information about materials, stresses, and tolerances.

On large capacitors, the designations are located directly on the body.

If there are no voltage markings, this is a low voltage device. There are conventional letter designations for voltages.

Polarity is indicated by “+ -” or a ring-shaped groove near the negative terminal. If this symbol is present, please strictly observe the polarity!

Capacitors(from Latin condenso - compact, thicken) - these are radioelements with concentrated electrical capacitance formed by two or more electrodes (plates) separated by a dielectric (special thin paper, mica, ceramics, etc.). The capacitance of the capacitor depends on the size (area) of the plates, the distance between them and the properties of the dielectric.

An important property of a capacitor is that for alternating current it represents resistance, the value of which decreases with increasing frequency.

The main units for measuring the capacitance of capacitors are: Farad, microFarad, nanoFarad, picofarad, the designations on capacitors for which look like: F, μF, nF, pF.

Like resistors, capacitors are divided into capacitors of constant capacitance, capacitors of variable capacitance (VCA), tuning and self-regulating capacitors. The most common are fixed capacitors.

They are used in oscillatory circuits, various filters, as well as for separating DC and AC circuits and as blocking elements.

Fixed capacitors

The conventional graphic designation of a constant-capacity capacitor—two parallel lines—symbolizes its main parts: two plates and a dielectric between them (Fig. 1).

Rice. 1. Fixed capacitors and their designation.

Near the capacitor designation on the diagram, its rated capacitance and sometimes its rated voltage are usually indicated. The basic unit of capacitance is the farad (F) - the capacitance of such an isolated conductor, the potential of which increases by one volt with an increase in charge by one coulomb.

This is a very large value, which is not used in practice. In radio engineering, capacitors with capacities ranging from fractions of a picofarad (pF) to tens of thousands of microfarads (μF) are used. Recall that 1 µF is equal to one millionth of a farad, and 1 pF is one millionth of a microfarad or one trillionth of a farad.

According to GOST 2.702-75, the nominal capacitance from 0 to 9,999 pF is indicated on the circuits in picofarads without designating the unit of measurement, from 10,000 pF to 9,999 μF - in microfarads with the designation of the unit of measurement by the letters mk (Fig. 2).

Rice. 2. Designation of units of measurement for capacitance of capacitors in the diagrams.

Capacitance designation on capacitors

The rated capacitance and the permissible deviation from it, and in some cases the rated voltage, are indicated on the capacitor housings.

Depending on their size, the nominal capacity and permissible deviation are indicated in full or abbreviated (coded) form.

The full designation of capacitance consists of the corresponding number and unit of measurement, and, as in the diagrams, capacitance from 0 to 9,999 pF is indicated in picofarads (22 pF, 3,300 pF, etc.), and from 0.01 to 9,999 µF - in microfarads (0.047 µF, 10 µF, etc.).

In abbreviated marking, the units of measurement of capacitance are designated by the letters P (picofarad), M (microfarad) and N (nanofarad; 1 nano-farad = 1000 pF = 0.001 μF).

At the same time Capacitance from 0 to 100 pF is indicated in picofarads, placing the letter P either after the number (if it is an integer) or in place of the decimal point (4.7 pF - 4P7; 8.2 pF - 8P2; 22 pF - 22P; 91 pF - 91P, etc.).

Capacitance from 100 pF (0.1 nF) to 0.1 µF (100 nF) is indicated in nanofarads, and from 0.1 µF and above - in microfarads.

In this case, if the capacitance is expressed in fractions of a nanofarad or microfarad, the corresponding the unit of measurement is placed in place of zero and comma(180 pF = 0.18 nF - H18; 470 pF = 0.47 nF - H47; 0.33 µF - MZZ; 0.5 µF - MbO, etc.), and if the number consists of an integer part and a fraction - at the decimal point (1500 pF = 1.5 nF - 1H5; 6.8 µF - 6M8, etc.).

Capacitances of capacitors, expressed as an integer number of corresponding units of measurement, are indicated in the usual way (0.01 μF - 10N, 20 μF - 20M, 100 μF - 100M, etc.). To indicate the permissible deviation of capacitance from the nominal value, the same coded designations are used as for resistors.

Features and requirements for capacitors

Depending on the circuit in which capacitors are used, different requirements apply to them. requirements. Thus, a capacitor operating in an oscillating circuit must have low losses at the operating frequency, high stability of capacitance over time and with changes in temperature, humidity, pressure, etc.

Capacitor losses, determined mainly by losses in the dielectric, increase with increasing temperature, humidity and frequency. Capacitors with a dielectric made of high-frequency ceramics, mica and film dielectrics have the lowest losses, while capacitors with a paper dielectric and ferroelectric ceramics have the highest losses.

This circumstance must be taken into account when replacing capacitors in radio equipment. A change in capacitance of a capacitor under the influence of the environment (mainly its temperature) occurs due to changes in the dimensions of the plates, the gaps between them and the properties of the dielectric.

Depending on the design and dielectric used, capacitors are characterized by different temperature coefficient of the container(TKE), which shows the relative change in capacitance with a change in temperature by one degree; TKE can be positive or negative. Based on the value and sign of this parameter, capacitors are divided into groups, which are assigned the corresponding letter designations and body color.

To maintain the tuning of oscillatory circuits when operating over a wide temperature range, they often use series and parallel connections of capacitors in which TKE have different signs. Due to this, when the temperature changes, the tuning frequency of such a temperature-compensated circuit remains practically unchanged.

Like any conductors, capacitors have some inductance. The larger it is, the longer and thinner the leads of the capacitor, the larger the size of its plates and internal connecting conductors.

They have the highest inductance paper capacitors, in which the facings are made in the form of long strips of foil, rolled together with the dielectric into a round or other shaped roll. Unless special measures are taken, such capacitors do not perform well at frequencies above a few megahertz.

Therefore, in practice, to ensure the operation of a blocking capacitor in a wide frequency range, a ceramic or mica capacitor of small capacity is connected in parallel with the paper capacitor.

However, there are paper capacitors with low self-inductance. In them, strips of foil are connected to the terminals not in one, but in many places. This is achieved either by strips of foil inserted into the roll during winding, or by moving the strips (linings) to opposite ends of the roll and soldering them (Fig. 1).

Feed-through and reference capacitors

To protect against interference that can penetrate into the device through the power supply circuits and vice versa, as well as for various interlocks, so-called pass capacitors. Such a capacitor has three terminals, two of which are a solid current-carrying rod passing through the capacitor body.

One of the capacitor plates is attached to this rod. The third terminal is a metal body to which the second plate is connected. The body of the pass-through capacitor is fixed directly to the chassis or screen, and the current-carrying wire (power circuit) is soldered to its middle terminal.

Thanks to this design, high-frequency currents are short-circuited to the chassis or screen of the device, while direct currents pass unimpeded.

Used at high frequencies ceramic feed-through capacitors, in which the role of one of the plates is played by the central conductor itself, and the other is the metallization layer deposited on the ceramic tube. These design features are also reflected by the conventional graphic designation of a pass-through capacitor (Fig. 3).

Rice. 3. Appearance and image on the diagrams of feed-through and support capacitors.

The outer lining is designated either in the form of a short arc (a), or in the form of one (b) or two (c) straight line segments with leads from the middle. The last designation is used when depicting a pass-through capacitor in the screen wall.

For the same purpose as checkpoints, they are used reference capacitors, which are a kind of mounting racks mounted on a metal chassis. The plate connected to it is distinguished in the designation of such a capacitor by three inclined lines, symbolizing “grounding” (Fig. 3d).

Oxide capacitors

To operate in the audio frequency range, as well as to filter rectified supply voltages, capacitors are needed, the capacitance of which is measured in tens, hundreds and even thousands of microfarads.

Such capacity with sufficiently small dimensions has oxide capacitors(old name - electrolytic). In them, the role of one plate (anode) is played by an aluminum or tantalum electrode, the role of a dielectric is played by a thin oxide layer deposited on it, and the role of the other plate (cathode) is a special electrolyte, the output of which is often the metal body of the capacitor.

Unlike others most types of oxide capacitors are polar, i.e., they require a polarizing voltage for normal operation. This means that they can only be turned on in DC or pulsating voltage circuits and only in the polarity (cathode to minus, anode to plus) indicated on the housing.

Failure to comply with this condition leads to failure of the capacitor, which is sometimes accompanied by an explosion!

Oxide capacitor switching polarity are shown in the diagrams with a “+” sign, depicted near the plate that symbolizes the anode (Fig. 4, a).

This is the general designation for a polarized capacitor. Along with it, specifically for oxide capacitors, GOST 2.728-74 established a symbol in which the Positive plate is depicted as a narrow rectangle (Fig. 4.6), and the “+” sign can be omitted in this case.

Rice. 4. Oxide capacitors and their designation on circuit diagrams.

In circuits of radio-electronic devices, you can sometimes find the designation of an oxide capacitor in the form of two narrow rectangles (Fig. 4, c). This is a symbol of a non-polar oxide capacitor that can operate in alternating current circuits (i.e. without polarizing voltage).

Oxide capacitors are very sensitive to overvoltage, so diagrams often indicate not only their rated capacitance, but also their rated voltage.

In order to reduce the size, two capacitors are sometimes placed in one housing, but only three leads are made (one is common). The symbol of a dual capacitor clearly conveys this idea (Fig. 4d).

Variable capacitors (VCA)

Variable capacitor consists of two groups of metal plates, one of which can move smoothly in relation to the other. During this movement, the plates of the moving part (rotor) are usually inserted into the gaps between the plates of the stationary part (stator), as a result of which the area of ​​overlap of one plate by another, and therefore the capacitance, changes.

Dielectric In the KPI, air is most often used. In small-sized equipment, for example, in transistor pocket receivers, CPE with a solid dielectric, which is used as films of wear-resistant high-frequency dielectrics (fluoroplastic, polyethylene, etc.), are widely used.

The parameters of PCBs with a solid dielectric are somewhat worse, but they are much cheaper to produce and their dimensions are much smaller than PCBs with an air dielectric.

We have already met the symbol KPI - this is the symbol of a constant-capacity capacitor crossed out by a regulation sign. However, from this designation it is not clear which of the plates symbolizes the rotor and which symbolizes the stator. To show this in the diagram, the rotor is depicted as an arc (Fig. 5).

Rice. 5. Designation of variable capacitors.

The main parameters of the KPI, which allow us to evaluate its capabilities when operating in an oscillatory circuit, are the minimum and maximum capacitance, which, as a rule, are indicated on the diagram next to the KPI symbol.

In most radio receivers and radio transmitters, KPI blocks consisting of two, three or more sections are used to simultaneously tune several oscillatory circuits.

The rotors in such blocks are mounted on one common shaft, by rotating which you can simultaneously change the capacity of all sections. The outer plates of the rotors are often split (along the radius). This allows you to adjust the unit at the factory so that the capacities of all sections are the same in any position of the rotor.

The capacitors included in the KPI block are shown separately in the diagrams. To show that they are combined into a block, i.e., controlled by one common handle, arrows indicating regulation are connected by a dashed line of mechanical connection, as shown in Fig. 6.

Rice. 6. Designation of dual variable capacitors.

When depicting the block's KPIs in different, far apart parts of the diagram, the mechanical connection is not shown, limiting itself only to the corresponding numbering of sections in the position designation (Fig. 6, sections C 1.1, C 1.2 and C 1.3).

In measuring equipment, for example in the arms of capacitive bridges, so-called differential capacitors(from Latin differentia - difference).

They have two groups of stator and one rotor plates, arranged so that when the rotor plates exit the gaps between the plates of one stator group, they at the same time enter between the plates of the other.

In this case, the capacitance between the plates of the first stator and the rotor plates decreases, and between the plates of the rotor and the second stator increases. The total capacitance between the rotor and both stators remains unchanged. Such capacitors are depicted in diagrams, as shown in Fig. 7.

Rice. 7. Differential capacitors and their designation on the diagrams.

Trimmer capacitors. To set the initial capacitance of the oscillating circuit, which determines the maximum frequency of its tuning, tuning capacitors are used, the capacitance of which can be changed from a few picofarads to several tens of picofarads (sometimes more).

The main requirement for them is a smooth change in capacity and reliable fixation of the rotor in the position set during adjustment. The axes of trimming capacitors (usually short) have a slot, so adjusting their capacitance is only possible with the use of a tool (screwdriver). In broadcasting equipment, capacitors with a solid dielectric are most widely used.

Rice. 8. Trimmer capacitors and their designation.

The design of a ceramic trimmer capacitor (CTC) of one of the most common types is shown in Fig. 8, a. It consists of a ceramic base (stator) and a ceramic disk (rotor) movably mounted on it.

The capacitor plates—thin layers of silver—are applied by burning onto the stator and the outside of the rotor. The capacity is changed by rotating the rotor. In the simplest equipment, wire tuning capacitors are sometimes used.

Such an element consists of a piece of copper wire with a diameter of 1 ... 2 and a length of 15 ... 20 mm, on which an insulated wire with a diameter of 0.2 ... 0.3 mm is wound tightly, turn to turn (Fig. 8, b). The container is changed by unwinding the wire, and to prevent the winding from slipping, it is impregnated with some kind of insulating compound (varnish, glue, etc.).

Trimmer capacitors denoted on the diagrams by the main symbol crossed out by the tuning control sign (Fig. 8, c).

Self-regulating capacitors

Using special ceramics as a dielectric, the dielectric constant of which strongly depends on the electric field strength, you can obtain a capacitor whose capacitance depends on the voltage on its plates.

Such capacitors are called varicondas(from the English words vari (able) - variable and cond (enser) - capacitor). When the voltage changes from a few volts to the nominal value, the capacitance of the variconde changes by 3-6 times.

Rice. 9. Varicond and its designation on the diagrams.

Varicondas can be used in various automation devices, in swing frequency generators, modulators, for electrical adjustment of oscillatory circuits, etc.

Symbol for variconda- a capacitor symbol with a sign of nonlinear self-regulation and the Latin letter U (Fig. 9, a).

The designation of thermal capacitors used in electronic wristwatches is constructed in a similar way. The factor that changes the capacitance of such a capacitor—the temperature of the environment—is designated by the symbol t° (Fig. 9, b). However, what is a capacitor is often searched for

Literature: V.V. Frolov, Language of radio circuits, Moscow, 1998.

In electrical stores, capacitors can most often be seen in the form of a cylinder, inside of which there are many strips of plates and dielectrics.

Capacitor - what is it?

A capacitor is part of an electrical circuit consisting of 2 electrodes that are capable of accumulating, focusing or transmitting current to other devices. Structurally, the electrodes are capacitor plates with opposite charges. In order for the device to work, a dielectric is placed between the plates - an element that prevents the two plates from touching each other.

The definition of condenser comes from the Latin word “condenso”, which means compaction, concentration.

Elements for soldering containers are used to transport, measure, redirect and transmit electricity and signals.

Where are capacitors used?

Every novice radio amateur often asks the question: what is a capacitor for? Beginners do not understand why it is needed and mistakenly believe that it can fully replace a battery or power supply.

All radio devices include capacitors, transistors and resistors. These elements make up a board or an entire module in circuits with static values, which makes it the basis for any electrical appliance, from a small iron to industrial devices.

The use of capacitors is most often observed as:

1. Filter element for high frequency and low frequency interference;
2. Levels sudden surges in alternating current, as well as for static and voltage on the capacitor;
3. Voltage ripple equalizer.

The purpose of the capacitor and its functions are determined by the purposes of use:

1. General purpose. This is a capacitor, the design of which contains only low-voltage elements located on small circuit boards, for example, devices such as a television remote control, radio, kettle, etc.;
2. High voltage. The capacitor in the DC circuit supports high-voltage industrial and technical systems;
3. Pulse. Capacitive generates a sharp voltage surge and supplies it to the receiving panel of the device;
4. Launchers. Used for soldering in those devices that are designed to start, turn on/off devices, for example, a remote control or control unit;
5. Noise suppressing. The capacitor in the AC circuit is used in satellite, television and military equipment.

Types of capacitors

The design of the capacitor is determined by the type of dielectric. It comes in the following types:

1. Liquid. A dielectric in liquid form is rare; this type is mainly used in industry or for radio devices;
2. Vacuum. There is no dielectric in the capacitor, but instead there are plates in a sealed housing;
3. Gaseous. Based on the interaction of chemical reactions and used for the production of refrigeration equipment, production lines and installations;
4. Electrolytic capacitor. The principle is based on the interaction of a metal anode and an electrode (cathode). The oxide layer of the anode is the semiconductor part, as a result of which this type of circuit element is considered the most productive;
5. Organic. The dielectric can be paper, film, etc. It is not able to accumulate, but only slightly level out voltage surges;
6. Combined. This includes metal-paper, paper-film, etc. The efficiency increases if the dielectric contains a metal component;
7. Inorganic. The most common ones are glass and ceramic. Their use is determined by durability and strength;
8. Combined inorganic. Glass-film, as well as glass-enamel, which have excellent leveling properties.

Types of capacitors

The elements of the radio board differ in the type of capacitance change:

1. Permanent. The cells maintain a constant voltage capacity until the end of their shelf life. This type is the most common and universal, as it is suitable for making any type of device;
2. Variables. They have the ability to change the volume of the container when using a rheostat, varicap or when the temperature changes. The mechanical method using a rheostat involves soldering an additional element onto the board, while when using a variconde, only the amount of incoming voltage changes;
3. Trimmers. They are the most flexible type of capacitor, with the help of which you can quickly and efficiently increase the throughput of the system with minimal reconstruction.

Operating principle of a capacitor

Let's look at how a capacitor works when connected to a power source:

1. Charge accumulation. When connected to the network, the current is directed to the electrolytes;
2. Charged particles are distributed on the plate according to their charge: negative ones - into electrons, and positive ones - into ions;
3. The dielectric serves as a barrier between the two plates and prevents particles from mixing.

The capacitance of a capacitor is determined by calculating the ratio of the charge of one conductor to its potential power.

Important! The dielectric is also capable of removing the resulting voltage on the capacitor during operation of the device.

Capacitor Characteristics

The characteristics are conventionally divided into points:

1. The amount of deviation. Before entering the store, each capacitor must undergo a series of tests on the production line. After testing each model, the manufacturer indicates the range of permissible deviations from the original value;
2. Voltage value. Mostly elements with a voltage of 12 or 220 Volts are used, but there are also 5, 50, 110, 380, 660, 1000 and more Volts. In order to avoid capacitor burnout and dielectric breakdown, it is best to purchase an element with a voltage reserve;
3. Permissible temperature. This parameter is very important for small devices operating on a 220 Volt network. As a rule, the higher the voltage, the higher the permissible temperature level for operation. Temperature parameters are measured using an electronic thermometer;
4. Availability of direct or alternating current. Perhaps one of the most important parameters, since the performance of the designed equipment completely depends on it;
5. Number of phases. Depending on the complexity of the device, single-phase or three-phase capacitors can be used. To connect an element directly, a single-phase one is sufficient, but if the board is a “city”, then it is recommended to use a three-phase one, as it distributes the load more smoothly.

What does capacity depend on?

The capacitance of the capacitor depends on the type of dielectric and is indicated on the case, measured in uF or uF. It ranges from 0 to 9,999 pF in picofarads, while in microfarads it ranges from 10,000 pF to 9,999 µF. These characteristics are specified in the state standard GOST 2.702.

Pay attention! The larger the electrolyte capacity, the longer the charging time, and the more charge the device can transfer.

The greater the load or power of the device, the shorter the discharge time. In this case, resistance plays an important role, since the amount of outgoing electrical flow depends on it.

The main part of the capacitor is the dielectric. It has the following number of characteristics that affect the power of the equipment:

1. Insulation resistance. This includes both internal and external insulation made from polymers;
2. Maximum voltage. The dielectric determines how much voltage the capacitor is capable of storing or transmitting;
3. The amount of energy loss. Depends on the configuration of the dielectric and its characteristics. Typically, energy dissipates gradually or in sharp bursts;
4. Capacity level. In order for a capacitor to store a small amount of energy for a short period of time, it needs to maintain a constant volume of capacitance. Most often, it fails precisely because of the inability to pass a given amount of voltage;

Good to know! The abbreviation “AC” located on the element body denotes alternating voltage. The accumulated voltage on the capacitor cannot be used or transmitted - it must be extinguished.

Capacitor properties

The capacitor acts as:

1. Inductive coil. Let's take the example of a regular light bulb: it will light up only if you connect it directly to an AC source. This leads to the rule that the larger the capacity, the more powerful the luminous flux of the light bulb;
2. Charge storage. Properties allow it to quickly charge and discharge, thereby creating a powerful impulse with low resistance. Used for the production of various types of accelerators, laser systems, electric flashes, etc.;
3. The battery received charge. A powerful element is capable of maintaining the received portion of current for a long time, while it can serve as an adapter for other devices. Compared to a rechargeable battery, a capacitor loses some of its charge over time, and is also not able to accommodate a large amount of electricity, for example, for industrial scale;
4. Charging the electric motor. The connection is made through the third terminal (operating voltage of the capacitor is 380 or 220 Volts). Thanks to the new technology, it has become possible to use a three-phase motor (with a phase rotation of 90 degrees), using a standard network;
5. Compensator devices. It is used in industry to stabilize reactive energy: part of the incoming power is dissolved and adjusted at the output of the capacitor to a certain volume.

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