First capacitor. Types of capacitors and their application. Features of the use of electrolytic capacitors

In the electrical circuit of each device there is such an element as a capacitor. It is he who serves to fill the energy that is needed for the correct and uninterrupted operation of the equipment.

What is a capacitor

Each capacitor is a device with a set technical parameters which are worth considering in detail.

Capacitors can be found in many branches of electrical engineering. Their immediate scope:

• Creation of circuits, oscillatory circuits.
• Getting a boost with a lot of power.
• In industrial electrical engineering.
• in the manufacture of sensors.
• Improving the operation of protective devices.

Capacitor capacity

For each capacitor, the main parameter is its capacitance. Each device has its own and it is measured in farads. At the heart of electronics and radio engineering, capacitors with a millionth of a farad are used. To find out the nominal capacity of the device, just look at its case, which contains all the information. Capacity readings may vary due to the following parameters:

• The total area of ​​all covers.
• distance between them.
• The material from which the dielectric is made.
• Ambient temperature.

Along with the nominal capacity, there is also a real one. Its value is much lower than the previous one. By real capacitance, you can determine the main electrical parameters. The capacitance is determined from the charge of the plate and its voltage. The maximum capacitance can reach several tens of farads. A capacitor can also be characterized by its specific capacitance. This is the ratio of the capacitance and the volume of the dielectric. The small thickness of the dielectric provides great importance specific capacity. Each capacitor can change its capacitance, and they are divided into the following types:

• Fixed capacitors - they practically do not change their capacitance.
• Variable capacitors - the capacitance value changes during the operation of the equipment.
• Trimmer capacitors - change their capacitance from adjusting the equipment.

Capacitor voltage

Voltage is considered another important parameter. In order for the capacitor to perform its functions in full, you need to know the exact voltage reading. It is indicated on the body of the device. The rated voltage directly depends on the complexity of the capacitor design and the basic properties of the materials used in its manufacture. The voltage applied to the capacitor must be exactly the same as the nominal voltage. Many devices heat up during operation, in which case the voltage drops. Often, due to the large difference in voltages, the capacitor can burn out or explode. It is also due to leakage or increased resistance. For safe operation of the capacitor, it is equipped with a protective valve and a notch on the body. As soon as there is an increase in pressure, the valve automatically opens, and the body breaks along the intended notch. In this case, the electrolyte leaves the capacitor in the form of a gas and no explosion occurs.

Capacitor tolerances

The simplest capacitor is two electrodes made in the form of plates, which are separated by thin insulators. Each device has a deviation that is permissible during its operation. This value can also be found by marking the device. Its tolerance is measured and indicated as a percentage and can range from 20 to 30%. For electrical engineering, which must work with high accuracy, capacitors with a small tolerance value, not more than 1%, can be used.
The given parameters are basic for the operation of the capacitor. Knowing their values, you can use capacitors to self assembly devices or machines.

Types of capacitors

There are several main types of capacitors that are used in various techniques. So, it is worth considering each type, its descriptions and properties:

Each capacitor has its own purpose, so they are additionally classified into general and special. Common capacitors are used in all types and classes of equipment. Basically, these are low-voltage devices. Special capacitors are all other types of devices that are high-voltage, pulse, starting and other various types.

Features of a flat capacitor

Since a capacitor is a device designed to accumulate voltage and distribute it further, therefore, you need to choose it with good electrical capacity and "breakdown" voltage. One of these is a flat capacitor. It is produced in the form of two thin plates of a certain area, which are located at a close distance from each other. A flat capacitor has two charges: positive and negative.

The plates of a flat capacitor between themselves have a uniform electric field. This type of device does not interact with other devices. The capacitor plate is capable of amplifying the electric field.

Correct capacitor charge

It is a storehouse for electrical charges that must be constantly recharged. The capacitor is charged by connecting it to the network. To charge the device, you need to connect it correctly. To do this, they take a circuit that consists of a discharged capacitor with a capacitance, a resistor, and connect it to a power supply with a constant voltage.

The capacitor is discharged according to the following type: the key is closed, and its plates are connected to each other. At this time, the capacitor is discharged, and the electric field between its plates disappears. If the capacitor is discharged through the wires, then it will take a long time, as a lot of energy accumulates in them.

Why do we need a capacitor circuit

The circuits contain capacitors, which are made from a pair of plates. They are made from aluminum or brass. Good job radio engineering depends on the correct setting of the circuits. The most common circuit circuit consists of one coil and a capacitor, which are interconnected in an electrical circuit. There are conditions that affect the appearance of oscillations, so most often the capacitor circuit is called oscillatory.

Conclusion

A capacitor is a passive device in an electrical circuit that is used as a container to store electricity. To a means to store energy in electrical circuits, called a capacitor, worked for a long time, you need to follow the specified conditions that are written on the device case. The scope is wide. Capacitors are used in radio electronics and various equipment. Devices are divided into many different types and are produced in a variety of designs. Capacitors can be connected in two ways: parallel and series. Also on the body of the device there is information about the capacity, voltage, tolerance and its type. It is worth remembering that when connecting the capacitor, it is worth observing the polarity. Otherwise, the device will quickly fail.

Capacitors, like resistors, are among the most numerous elements of radio engineering devices. On some properties of a capacitor- "store" electric charges I have already told. Then he said that the capacitance of the capacitor will be the more significant, the larger the area of ​​​​its plates and the thinner the dielectric layer between them.

The basic unit of electrical capacitance is the farad (abbreviated F, named after the English physicist M. Faraday. However, 1 F is this is a very large capacity. The globe, for example, has a capacitance of less than 1 F. In electrical and radio engineering, they use a unit of capacitance equal to a millionth of a farad, which is called a microfarad (abbreviated microfarad). There are 1,000,000 microfarads in one farad, i.e., 1 microfarad = 0.000001 F. But even this unit of capacitance is often too large. Therefore, there is an even smaller unit of capacitance called a picofarad (abbreviated as pF), which is a millionth of a microfarad, i.e. 0.000001 microfarad; 1 uF = 1000000 pF. All capacitors, whether constant or variable, are characterized primarily by their capacitances, expressed respectively in picofarads, microfarads.

On circuit diagrams the capacitance of capacitors from 1 to 9999 pF is indicated by integers corresponding to their capacitances in these units without pF designation, and the capacitance of capacitors is from 0.01 μF (10000 pF) and more— in fractions of microfarads or microfarads without the designation of microfarads. If the capacitance of the capacitor is equal to an integer number of microfarads, then in contrast to the capacitance designation in picofarads after the last significant digit put a comma and zero. Examples of designation of capacitor capacities in the diagrams: C1 \u003d 47 corresponds to 47 pF, C2 \u003d 3300 corresponds to 3300 pF; C3 \u003d 0.47 corresponds to 0.047 μF (47000 pF); C4 = 0.1 corresponds to 0.1 uF; C5 = 20.0 corresponds to 20 uF.

A capacitor in its simplest form consists of two plates separated by a dielectric. If a capacitor is connected to a DC circuit, then the current in this circuit will stop. Yes, this is understandable: through the insulator, which is the dielectric of the capacitor, direct current cannot flow. The inclusion of a capacitor in a DC circuit is equivalent to breaking it (we do not take into account the moment of inclusion, when a short-term capacitor charging current appears in the circuit). A capacitor behaves differently in an alternating current circuit. Remember: the polarity of the voltage at the terminals of an AC power source changes periodically. This means that if you include a capacitor in a circuit powered by such a current source, its plates will alternately recharge with the frequency of this current. As a result, alternating current will flow in the circuit.

A capacitor, like a resistor and a coil, offers resistance to alternating current, but it is different for currents of different frequencies. It can pass high frequency currents well and at the same time be almost an insulator for low frequency currents. Radio amateurs, for example, sometimes use electric lighting wires instead of external antennas, connecting receivers to them through a capacitor with a capacity of 220– 510 pF. Is this capacitance randomly chosen? No, not by chance. A capacitor of such a capacity passes well the high-frequency currents necessary for the operation of the receiver, but has a high resistance to the 50 Hz alternating current flowing in the network. In this case, the capacitor becomes a kind of filter that passes high-frequency current and delays low-frequency current.

The capacitance of a capacitor to alternating current depends on its capacitance and the frequency of the current: the greater the capacitance of the capacitor and the frequency of the current, the lower its capacitance. This capacitor resistance can be determined with sufficient accuracy by such a simplified formula

RC=1/6fC
π (more precisely 6.28, sinceπ = 3.14).

where RC is the capacitance of the capacitor, Ohm; f - current frequency, Hz; C is the capacitance of this capacitor, F; digit 6 - rounded to whole units value 2π (more precisely 6.28, sinceπ = 3.14).

Using this formula, let's find out how a capacitor behaves with respect to alternating currents, if you use the mains wires as an antenna. Let's say that the capacitance of this capacitor is 500 pF (500 pF = 0.0000000005 F). Mains current frequency 50 Hz. For the average carrier frequency of the radio station, we will take 1 MHz (1,000,000 Hz), which corresponds to a wave length of 300 m. What resistance does this capacitor provide to the radio frequency?

Rc \u003d\u003d 1 / (6 1000000 0.0000000005) ~ \u003d 300 Ohm.

What about AC power?

Rc = 1/(6 50 0.0000000005) ~= 7 MΩ.

And here is the result: a 500 pF capacitor provides 20,000 times less resistance to high frequency current than to low frequency current. Earnestly? A smaller capacitor provides even more resistance to the alternating current of the network.

the capacitance of a capacitor to alternating current decreases with an increase in its capacitance and current frequency, and vice versa, increases with a decrease in its capacitance and current frequency.

The property of a capacitor not to pass direct current and to conduct alternating currents of different frequencies in different ways is used to separate pulsating currents into their components, delay currents of some frequencies and pass currents of other frequencies.

How are fixed capacitors arranged?

All capacitors of constant capacitance have conductive plates, and between them - ceramic, mica, paper, or some other solid dielectric. According to the type of dielectric used, capacitors are called ceramic, mica, paper, respectively. Appearance some ceramic capacitors of constant capacitance is shown in fig. 1

Rice. 1. Ceramic fixed capacitors

They have special ceramics as a dielectric, plates— thin layers of silver-plated metal deposited on the surface of ceramics, and brass silver-plated wires or strips soldered to the plates. From above, the capacitor cases are covered with enamel.

The most common are ceramic capacitors of the KDK (Disk Ceramic Capacitor) and KTK (Tubular Ceramic Capacitor) types: In a KTK type capacitor, one lining is applied to the inner, and the second to the outer surface of a thin-walled ceramic tube. Sometimes tubular capacitors are placed in sealed porcelain "cases" with metal caps at the ends. These are capacitors of the KGK type.

Ceramic capacitors have relatively small capacitances - up to several thousand picofarads. They are placed in those circuits in which high-frequency current flows (antenna circuit, oscillatory circuit), for communication between them.

To get a capacitor small size, but having a relatively large capacity, it is made not from two, but from several plates stacked and separated from each other by a dielectric (Fig. 2). In this case, each pair of adjacent plates forms a capacitor. By connecting these pairs of plates in parallel, a capacitor of considerable capacity is obtained.

Rice. 2. Mica capacitors

This is how all capacitors with a mica dielectric are arranged. Their plates— the plates are sheets of aluminum foil or layers of silver deposited directly on the mica, and the leads are pieces of silver-plated wire. Such capacitors are molded with plastic. These are KSO capacitors. In their name there is a number characterizing the shape and size of capacitors, for example: KSO-1, KSO-5. The larger the number, the larger the capacitor. Some mica capacitors are available in waterproof ceramic cases. They are called SGM type capacitors. The capacitance of mica capacitors is from 47 to 50,000 pF (0.05 microfarads). Like ceramic, they are designed for high-frequency circuits, as well as for use as interlocks and for communication between high-frequency circuits.

In paper capacitors (Fig. 3), thin paper impregnated with paraffin serves as a dielectric, and the plates are foil. The strips of paper, together with the covers, are rolled up and placed in a cardboard or metal case. The wider and longer the plates, the greater the capacitance of the capacitor.

Rice. 3. Paper and metal-paper fixed capacitors

Paper capacitors are mainly used in low-frequency circuits, as well as for blocking power supplies. There are many types of paper dielectric capacitors. And all have the letter B (Paper) in their designation. Capacitors of the BM type (Paper Small-sized) are enclosed in metal tubes filled with special resin at the ends.

KB capacitors have cardboard cylindrical cases. Capacitors of the KBG-I type are placed in porcelain cases with metal end caps connected to the plates, from which narrow output petals extend.

Capacitors with a capacity of up to several microfarads are produced in metal cases. These include capacitors of types KBG-MP, KBG-MN, KBGT. There can be two or three of them in one building.

The dielectric of capacitors of the MBM type (Metal Paper Small) is varnished capacitor paper, and the plates are layers of metal less than a micron thick applied to one side of the paper. Feature capacitors of this type— the ability to self-repair after an electrical breakdown of a dielectric.

A special group of capacitors of constant capacity are electrolytic (Fig. 4).

Rice. 4. Electrolytic capacitors

By internal device an electrolytic capacitor is somewhat reminiscent of a paper one. It has two aluminum foil strips. The surface of one of them is covered with a thin layer of oxide. Between the aluminum strips there is a strip of porous paper impregnated with a special thick liquid.— electrolyte. This four-layer strip is rolled up and placed in an aluminum cylindrical cup or cartridge.

The dielectric of the capacitor is an oxide layer. The positive lining (anode) is the tape that has an oxide layer. It is connected to a petal isolated from the body. The second, negative lining (cathode) paper, impregnated with electrolyte through a tape, on which there is no oxide layer, is connected to a heavy metal case. Thus, the case is a negative terminal, and the lobe isolated from it is terminal of the positive plate of the electrolytic capacitor. So, in particular, capacitors of the KE, K50-3 types are arranged. Capacitors KE-2 differ from capacitors of KE types only in a plastic sleeve with a thread and a nut for mounting on the panel. Aluminum cases of capacitors K50-3 have the shape of a cartridge with a diameter of 4.5– 6 and 15 20 mm long. conclusions— wire. Similarly arranged and capacitors type K50-6. But they have the leads of the electrodes (plates) isolated from the cases.

On the schematic diagrams, electrolytic capacitors are depicted in the same way as other capacitors of constant capacitance - two " dashes, but put a sign near the positive lining« + » .

Electrolytic capacitors have large capacitances— from fractions to several thousand microfarads. They are designed to operate in circuits with pulsating currents, such as filters in AC rectifiers, for coupling between low-frequency circuits. In this case, the negative electrode of the capacitor is connected to the negative pole of the circuit, and the positive— with its positive pole. If the polarity of the connection is not observed, the electrolytic capacitor may fail.

The nominal capacities of electrolytic capacitors are written on their cases. The actual capacity can be much larger than the nominal one.

The most important characteristic of any capacitor, except for the capacitance, is also its rated voltage, i.e. the voltage at which the capacitor can operate for a long time without losing its properties. This voltage depends on the properties and thickness of the dielectric layer of the capacitor. Ceramic, mica, paper and metal-paper capacitors various types designed for rated voltages from 150 to 1000 V and more.

Electrolytic capacitors are produced for rated voltages from a few volts to 30– 50 V and 150 to 450 – 500 V. In this regard, they are divided into two groups: low-voltage and high-voltage. The capacitors of the first group are used in circuits with a relatively low voltage, and the capacitors of the second group— in relatively high voltage circuits.

When choosing capacitors for your design, always pay attention to their voltage ratings. In a circuit with a lower voltage than the nominal one, capacitors can be turned on, but in a circuit with a voltage exceeding the nominal one, they cannot be turned on. If there is a voltage on the capacitor plates that exceeds its rated voltage, then the dielectric will break through. A broken capacitor is unusable.

Now about variable capacitors.

The device of the simplest variable capacitor is shown in fig. 5. One of its lining - the stator is stationary. Second rotor— attached to the axle. When the axis rotates, the overlapping area of ​​​​the plates, and with it the capacitance of the capacitor, change.

Rice. 5. The simplest capacitor variable capacity

Variable capacitors used in tuned oscillatory circuits of receivers consist of two groups of plates (Fig. 6, a) made of sheet aluminum or brass. The rotor plates are connected by an axis. The stator plates are also connected and insulated from the rotor. When the axis rotates, the plates of the stator group gradually enter the air gaps between the plates of the rotor group, which is why the capacitance of the capacitor changes smoothly. When the rotor plates are completely removed from the gaps between the stator plates, the capacitance of the capacitor is the smallest; it is called the initial capacitance of the capacitor. When the rotor plates are completely inserted between the stator plates, the capacitance of the capacitor will be the largest, that is, the maximum for this capacitor. The maximum capacitance of the capacitor will be the greater, the more plates it contains and the smaller the distance between the movable and fixed plates.

The capacitors shown in Fig. 5 and 6a, the dielectric is air. In small-sized capacitors of variable capacitance (Fig. 6, b), the dielectric can be paper, plastic films, ceramics. Such capacitors are called variable capacitors with a solid dielectric. While smaller than air dielectric capacitors, they can have significant maximum capacitances. It is these capacitors that are used to tune the oscillatory circuits of small-sized transistor receivers.

Rice. 7. One of the designs of a block of variable capacitors

Single capacitors and blocks of air dielectric variable capacitors require careful handling. Even a slight distortion or other damage to the plates leads to a short circuit between them. Correction of the capacitor plates— is a complicated matter.

Solid dielectric capacitors also include trimmer capacitors, which are a type of variable capacitors. Most often, such capacitors are used to adjust the circuits to resonance, so they are called trimmers. The designs of the most common trimmer capacitors are shown in fig. 8. Each of them consists of a relatively massive ceramic base and a thin ceramic disc. On the surface of the base (under the disk) and on the disk, metal layers are deposited in the form of sectors, which are the plates of the capacitor. When the disk rotates around the axis, the overlap area of ​​the sectors-plates changes, the capacitance of the capacitor changes.

The capacitance of trimmer capacitors is indicated on their cases as a fractional number, where the numerator is the smallest and the denominator is the largest capacitance of this capacitor. If, for example, 6/30 is indicated on the capacitor, then this means that its smallest capacitance is 6 pF, and the largest is 30 pF. Trimmer capacitors usually have the smallest capacitance 2 - 5 pF, and the largest up to 100– 150 pF. Some of them, such as KPK-2, can be used as variable capacitors for tuning simple single-loop receivers.

Capacitors, like resistors, can be connected in parallel or in series. The connection of capacitors is most often resorted to in cases where there is no capacitor of the required rating at hand, but there are others from which the necessary capacity can be made. If you connect the capacitors in parallel (Fig. 8, a), then their total capacitance will be equal to the sum of the capacitances of all connected capacitors, i.e.

Ctot = C1 + C2 + C3, etc.

So, for example, if C1 \u003d 33 pF and C2 \u003d 47 pF, then the total capacitance of these two capacitors will be: Ctot \u003d 33 + 47 \u003d 80 pF. When capacitors are connected in series (Fig. 8, b), their total capacitance is always less than the smallest capacitance included in the chain. It is calculated according to the formula

Ctot = C1 · С2/(С1 + С2)

For example, let's say C1 = 220pF and C2 = 330pF; then Ctot = 220 330/(220 + 330) = 132 pF. When two capacitors of the same capacitance are connected in series, their total capacitance will be half the capacitance of each of them.

Rice. 8. Parallel (a) and series (b) connection of capacitors

Capacitor

The basis of the capacitor design is two conductive plates, between which there is a dielectric

On the left are surface mount capacitors; right - capacitors for volumetric installation; top - ceramic; bottom - electrolytic.

Various capacitors for bulk mounting

Capacitor Properties

A capacitor in a DC circuit can conduct current at the moment it is connected to the circuit (the capacitor is being charged or recharged), at the end of the transient process, the current does not flow through the capacitor, since its plates are separated by a dielectric. In an alternating current circuit, it conducts alternating current oscillations by cyclically recharging a capacitor.

where is the imaginary unit, is the frequency of the flowing sinusoidal current, is the capacitance of the capacitor. It also follows that the reactance of the capacitor is: . For DC, the frequency is zero, hence the reactance of a capacitor is infinite (ideally).

On electrical circuit diagrams, the nominal capacitance of capacitors is usually indicated in microfarads (1 μF \u003d 10 6 pF) and picofarads, but often in nanofarads. With a capacitance of not more than 0.01 μF, the capacitance of the capacitor is indicated in picofarads, while it is permissible not to indicate the unit of measurement, i.e. the postfix "pF" is omitted. When designating the nominal capacity in other units, indicate the unit of measurement (picoFarad). For, as well as for high-voltage capacitors in the diagrams, after designating the capacitance rating, indicate their maximum operating voltage in volts (V) or kilovolts (kV). For example: "10 microns x 10 V". For indicate the range of change in capacitance, for example: "10 - 180". Currently, capacitors are manufactured with nominal capacities from decimal-logarithmic series of values ​​E3, E6, E12, E24, i.e. there are 3, 6, 12, 24 values ​​per decade, so that the values ​​with the appropriate tolerance (scatter) cover the entire decade.

Characteristics of capacitors

Main settings

Capacity

The main characteristic of a capacitor is its capacity. The value of the nominal capacity appears in the designation of the capacitor, while the actual capacity can vary significantly depending on many factors. The actual capacitance of a capacitor determines its electrical properties. So, by definition of capacitance, the charge on the plate is proportional to the voltage between the plates ( q = CU ). Typical capacitance values ​​for capacitors range from units of picofarads to hundreds of microfarads. However, there are capacitors with a capacity of up to tens of farads.

The capacitance of a flat capacitor, consisting of two parallel metal plates with an area each, located at a distance from each other, in the SI system is expressed by the formula: , where is the relative permittivity of the medium filling the space between the plates (this formula is valid only when much less linear dimensions plates).

To obtain large capacitances, capacitors are connected in parallel. In this case, the voltage between the plates of all capacitors is the same. Total battery capacity parallel connected capacitors is equal to the sum of the capacitances of all capacitors included in the battery.

If all capacitors connected in parallel have the same distance between the plates and the properties of the dielectric, then these capacitors can be represented as one large capacitor, divided into fragments of a smaller area.

When capacitors are connected in series, the charges of all capacitors are the same. Total battery capacity successively connected capacitors is

or

This capacitance is always less than the minimum capacitance of the capacitor included in the battery. However, when connected in series, the possibility of breakdown of capacitors is reduced, since each capacitor accounts for only a part of the potential difference of the voltage source.

If the area of ​​the plates of all capacitors connected in series is the same, then these capacitors can be represented as one large capacitor, between the plates of which there is a stack of dielectric plates of all the capacitors that make it up.

Specific capacity

Capacitors are also characterized by specific capacitance - the ratio of capacitance to the volume (or mass) of the dielectric. The maximum value of specific capacitance is achieved at the minimum thickness of the dielectric, however, its breakdown voltage decreases.

Rated voltage

Another, no less important characteristic of capacitors is the rated voltage - the voltage value indicated on the capacitor, at which it can operate under specified conditions during its service life while maintaining the parameters within acceptable limits.

The rated voltage depends on the design of the capacitor and the properties of the materials used. During operation, the voltage on the capacitor must not exceed the nominal voltage. For many types of capacitors, the allowable voltage decreases with increasing temperature.

Polarity

Capacitors destroyed without explosion due to temperature and voltage not suitable for working.

Many oxide dielectric (electrolytic) capacitors function only with the correct voltage polarity due to the chemical nature of the interaction of the electrolyte with the dielectric. With a reverse voltage polarity, electrolytic capacitors usually fail due to the chemical destruction of the dielectric, followed by an increase in current, boiling of the electrolyte inside and, as a result, with the likelihood of an explosion of the case.

Explosions of electrolytic capacitors are a fairly common phenomenon. The main cause of explosions is the overheating of the capacitor, caused in most cases by leakage or an increase in the equivalent series resistance due to aging (relevant for impulse devices). To reduce damage to other parts and personal injury in modern large-capacity capacitors, a valve is installed or a notch is made on the body (you can often see it in the shape of the letter X, K or T at the end). With an increase in internal pressure, the valve opens or the housing collapses along the notch, the evaporated electrolyte exits in the form of a corrosive gas, and the pressure drops without explosion and fragments.

Real capacitors, in addition to capacitance, also have their own resistance and inductance. With a high degree of accuracy, the equivalent circuit of a real capacitor can be represented as follows:

Capacitor insulation electrical resistance - r

Insulation resistance is the resistance of a capacitor direct current, determined by the ratio r = U / I ut, Where U is the voltage applied to the capacitor, I ut- leakage current.

Equivalent series resistance - R

Equivalent series resistance (ERS) ESR) is mainly due to the electrical resistance of the material of the plates and leads of the capacitor and the contact(s) between them, as well as losses in the dielectric. Typically, ESR increases with increasing frequency of the current flowing through the capacitor.

In most cases, this parameter can be neglected, but sometimes (for example, in the case of using electrolytic capacitors in the filters of switching power supplies), a sufficiently small value of it can be vital for the reliability of the device (see, for example, Capacitor plague (English) ) .

Equivalent series inductance - L

The equivalent series inductance is mainly due to the self-inductance of the plates and leads of the capacitor. At low frequencies (up to a few kilohertz) it is usually not taken into account due to its insignificance.

Loss tangent

The loss tangent is the ratio of the imaginary and real parts of the complex permittivity.

Tank Temperature Coefficient (TKE)

TKE - relative change in capacitance when the ambient temperature changes by one degree Celsius (Kelvin). Thus, the value of capacitance versus temperature is represented by a linear formula:

where ∆ T is the increase in temperature in °C or °K relative to the normal conditions under which the capacitance value is specified. TKE is used to characterize capacitors with a significant linear capacitance versus temperature. However, TKE is not determined for all types of capacitors. Capacitors having a non-linear dependence of capacitance on temperature, and capacitors with big departures capacities from the effect of ambient temperature in the designation have an indication of the relative change in capacity in the operating temperature range.

Dielectric absorption

If a charged capacitor is quickly discharged to zero voltage by connecting a low-resistance load, and then removing the load and observing the voltage at the capacitor terminals, we will see that the voltage slowly rises. This phenomenon has been named dielectric absorption or

IN Everyday life each person uses voltage converters, adapters and power supplies. But, few people think that the main function in the listed devices is performed by capacitors. It is popularly called "electrolytes". Their main feature is their small size and the ability to accumulate charge up to the level of their capacity.

In the field of radio engineering and electrics, an electrolytic capacitor is an element with a dielectric shell made of metal oxide, called the anode, and an internal capacity for accumulating charge, called the cathode. Due to this property, they are widely used in electrical appliances and radio devices. Capacitors are present in the circuits of radios, televisions, washing machines, air conditioners, computer equipment and in many other devices.

History of appearance and development

In 1875, French scientist Eugène Adrien Ducretet discovered the electrochemical process in some metals. Tantalum, niobium, zinc, titanium, cadmium, aluminum, antimony and others became samples of the study. These samples were used in the form of an anode (the positive pole of the power supply). Under the action of an electric field, an oxide layer appeared on their surfaces, which had valve characteristics.

In 1896, the scientist Karol Pollak sent an application to the patent office for inventing a capacitor. He proved with his own element that electrochemical processes must have a certain polarity at the metal-dielectric interface in order to form an oxide formation. Failure to comply with this polarity leads to dielectric losses and short circuits.

In Russia, for a long time, the manufacture of electrolytic capacitors was considered uneconomical. Although there were many arguments in scientific publications about which technologies can be applied to set up production. The first serious developments in the production of electrolytic capacitors appeared in our state in 1931. Their container was filled with liquid electrolyte. Today, the production of these elements is on a wide scale. Many world-famous companies are engaged in the manufacture of electrolytic capacitors.

Capacitor options by application

As you know from the school physics curriculum, capacitors are polar devices. They begin to function when the current is directed in one direction. Therefore, in practice, they are included in circuits with constant or pulsating voltage circuits.

Application in constant voltage circuits

The properties of a capacitor of this design are used:

1. for the accumulation of electrical energy in pulse generators, pulsed light sources, as well as for the magnetization of hard magnetic elements in the process of physical experiments;
2. to raise the current to a certain level in welding units, x-ray machines and copying devices;
3. for accurate operation of analog memory or analog sweep circuits;
4. for the formation of a power tool in electronic devices and electric drives.

In constant voltage circuits with pulsating superimposition

Characteristics of capacitors in DC circuits with pulsating superimposition apply:

1. to create band-pass filter sections together with resistors and inductors;
2. for shunting elements of an electronic type circuit by changing current;
3. for connecting sections of the circuit for alternating current with elements operating on a constant component;
4. for generating sawtooth and rectangular voltage in circuits of the relaxation type of the generator;
5. for rectifying voltage in rectifiers.

Purpose in variable voltage circuits

For AC circuits, capacitor manufacturers have created elements that have non-polar capacitance. In their design, they have additional elements and increased dimensions. They come in different capacities, filled with concentrated alkaline substances and acids.

They apply:

1. To improve the quality of electrical energy and increase the power factor. For example, aluminum electrolytic capacitors reduce the level of the reactive component, which increases the power factor to 0.999;
2. In inverter circuits and devices with thyristor rectifiers to reduce the influence of magnetic fields;
3. To improve the starting ability of an asynchronous type motor. Almost all starting circuits of single-phase electric motors contain capacitors.

By way of filling variable capacitor divided into types:

• with liquid dielectric;
• with dry filling;
• with oxide semiconductor parameters of capacitors;
• oxide-metal execution.

The anode of electrolytic capacitors is made of aluminum, niobium or tantalum foil. A capacitor with a variable capacitance of an oxide-semiconductor type has a cathode in the form of a ball of a semiconductor deposited on an oxide layer.

Capacitor design

Capacitors of different types and sizes are made of two elements - these are the plates and the capacitance (the distance between the covers) filled with a dielectric substance. Capacity is calculated by the formula:

C = ee0S/d where:

• S is the value of the lining area;
• d is the value of the distance between the plates;
• e0 is the electric component that determines the strength of the electric field of the vacuum space;
• e is the permittivity.

A feature of electrolytic capacitors is that they contain a layer of electrolytic substance between two foil covers, where one of them is covered with a semiconductor oxide film. Such electrolytes have linings inside, folded together with a separating paper layer impregnated with electrolyte. The capacitance of the capacitor depends on its thickness. The top ball is also covered with a release paper layer. Everything in the kit is rolled up "in a tube" and is in a metal case.

Metal plates in the form of contacts are soldered along the edges of the foil. They are designed to be connected to other circuit elements. Moreover, the output with a positive potential is covered with an oxide ball. The function of the cathode is performed by an electrolyte layer connected to the second plate.

With the help of electrochemical corrosion of the surface of the lining (corrugation) in the manufacturing process, the area of ​​the lining is increased. With the help of this technology, high-capacity capacitors are created.

Usually, the element under consideration functions without failure at normal temperature and undistorted voltage. For example, when the voltage increases above the norm, a new layer of oxides is formed, accompanied by heat release and gas formation. As a result, the pressure in the case rises sharply, and its strength is not able to cope with such a capacity. This can lead to an explosion and destruction of other elements of the chain.

Many companies make capacitors with a protective membrane. It breaks under the action of the formation of gases and blocks the explosion. The marking of such capacitors consists in applying a notch in the form of the letter "T", "Y" or the "+" sign.

Deciphering numbers and letters on the surface of the product

To correctly decipher the designations on the body of different elements, you need to know the units of measurement. For capacitors, remember that capacitance is measured in farads (F). It has the following ratios:

• 1µF (micro farad) F=10¯⁶F;
• 1mF (millifarad) F=10¯³F;
• n(nanofarad)F=10¯⁹;
• p(picofarad)F=10¯¹²F.

The marking of capacitors of large parameters is indicated directly on the element body. In some designs, the inscriptions have different designations. In such cases, it is better to focus on the values ​​\u200b\u200bspecified above.

On some modifications, the marking is in capital letters. For example, instead of 1mF is MF. You can also find that the marking contains a set of letters fd, which means farad. In addition, the cipher contains information that allows deviation from the face value in percentage terms. For example, if the marking contains 6000uF + 50% -70%, then it should be understood that this differs from the given nominal value by 50% -70%. That is, you can use a 9000uF or 1800uF capacitor. If there are no percentages, then you need to find a letter. Usually it looks like a symbol separate from the container. Each letter allows deviation from the nominal value.

After determining the rating and the allowed error, you need to proceed to determining the voltage value. It is denoted by numbers along with letters such as V, VDC, WV or VDCW. The designation WV stands for operating voltage. The numbers indicate the maximum allowed tolerances.

It is important to know! If there is no value on the surface indicating the voltage rating, then such capacitors can be used in low-voltage circuits of the circuit. You also need to remember that AC capacitors cannot be used in DC voltage circuits, and vice versa.

To determine the polarity of the terminals, the signs "+" and "-" are applied on the case. If they are not, then the capacitor is connected to the circuit by either side.

Digital transcript

The numbers on the case have their own interpretation. When only two numbers and one letter are indicated, the combination of numbers indicates the capacity. All other encodings need to be understood with a non-standard approach. They mainly depend on the design of the element.

The third digit is the zero multiplier. Therefore, decoding is performed by the final digit. If it is in the range from 0 to 6, then zeros are added to the first digits in the number of the specified third digit. For example, 373 means 37000.

When the last digit goes beyond 0-6, such as 8, the first digit must be multiplied by 0.01. Thus code 378 stands for 0.37. When the number 9 is at the end, then the combination of the first two numbers is multiplied by 0.1. Designation 379 should be read as 3.7.

When everything is clear from the combination of numbers with the capacity, then you need to know the unit of measurement.

Important to remember! Small capacitors are measured in picofarads, while large capacitors are measured in microfarads.

Letter encoding

The letter R in the first two characters should be understood as the designation of a comma used in the designation of a decimal fraction. For example, the code 4R1 is read as 4.1 pF. If the marking contains the letters p, n or u, then they should also be changed to a comma. For example, n61 means 0.61 nanofarads.

Mixed labeling

Such a code on the capacitor case includes letters and numbers, alternating each other. Usually it is applied according to the scheme "letter - number - letter". The first letter indicates the operating temperature of the safe state of the capacitor. The second digit is the temperature limit.

The third letter means the change in capacitance in the limit from the minimum temperature to the maximum allowable temperature. If there is a letter "A", then this is an accurate indicator. Its error is 0.1%. In the presence of the letter "V", the capacity indicator fluctuates between 22% -82%. It is very common to find capacitors with the letter "R", which means 15% deviation in capacitance from temperature changes.

Changing parameters during operation

To understand which capacitors are good and which are not, you need to know General characteristics, and remember how the parameters depend on each other. For example, the ability to emit gases in the operating mode kpe requires, when installing the circuit, to create a margin of allowable voltage in the range of 0.5-0.6 of its value. This is especially important when the circuit operates in an environment with elevated temperature conditions.

When using a capacitor in alternating current circuits, the dependence on the operating frequency must be taken into account. Normally, the operating frequency of the changing voltage should not deviate from 50 Hz. For higher frequencies, capacitors with a lower allowable voltage must be included. Otherwise, a strong heating of the dielectric will appear, which will lead to a rupture of the case.

Elements with high capacitance and low leakage currents are capable of retaining a charge for a long time. Therefore, it is important for safety to connect in parallel a resistive element with a resistance of at least 1 MΩ and a power of 0.5 W.

Electrical capacitors are used to store electrical energy. Without them, not a single radio circuit will function - and a television receiver. The advent of microchips changed the function of capacitors. Many of them are made in an integrated form.

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