First capacitor. What is a capacitor

In everyday life, every 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 also popularly called “electrolytes”. Their main feature is their small size and ability to accumulate charge to the level of their capacity.

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

History of appearance and development

In 1875, the French scientist Eugène Adrien Ducretet discovered the electrochemical process in certain metals. The research samples included tantalum, niobium, zinc, titanium, cadmium, aluminum, antimony and others. These samples were used in the form of an anode (positive pole of the power supply). Under the influence of an electric field, an oxide layer with valve characteristics appeared on their surfaces.

In 1896, scientist Karol Pollak submitted an application to the patent office to invent 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 observe this polarity leads to dielectric losses and short circuits.

In Russia, for a long time, the production of electrolytic capacitors was considered uneconomical. Although there were many arguments in scientific publications about what technologies could be used to set up production. The first serious developments in the production of electrolytic capacitors appeared in our country 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 production 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 precise operation of analog memory or analog sweep circuits;
4. for the formation of power tools in electronic devices and electric drives.

In constant voltage circuits with pulsating application

The characteristics of capacitors in DC circuits with pulsating overlay apply:

1. to create bandpass filter sections together with resistors and inductors;
2. for shunting electronic circuit elements with varying current;
3. for connecting sections of an alternating current circuit with elements operating on a direct component;
4. for generating sawtooth and square-wave voltages in relaxation-type generator circuits;
5. for rectifying voltage in rectifiers.

Purpose in variable voltage circuits

For alternating current 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 containers 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 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 for single-phase electric motors contain capacitors.

According to the filling method, the variable capacitor is divided into types:

• with liquid dielectric;
• with dry filling;
• with oxide semiconductor capacitor parameters;
• metal oxide design.

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

Capacitor design

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

C = ee0S/d, where:

• S – value of the lining area;
• d – value of the distance between the plates;
• e0 is the electrical component that establishes the electric field strength of vacuum space;
• e – dielectric constant.

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

Metal plates in the form of contacts are soldered along the edges of the foil. They are designed to connect to other circuit elements. Moreover, the terminal 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) during the manufacturing process, the area of ​​the lining is increased. Using this technology, high-capacity capacitors are created.

Typically, the element in question functions trouble-free at normal temperature and undistorted voltage. For example, when the voltage increases above normal, a new layer of oxides forms, accompanied by the release of heat and gas formation. As a result, the pressure in the housing increases sharply, and its strength is unable to cope with such a capacity. This may lead to an explosion and destruction of other circuit elements.

Many companies manufacture capacitors with a protective membrane. It breaks under the influence of the formation of gases and blocks the explosion. The marking of such capacitors consists of 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 various elements, you need to know the units of measurement. For capacitors, remember that capacitance is measured in farads (F). It has the following relationships:

• 1uF (microfarad)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 symbols. In such cases, it is better to rely on the values ​​indicated above.

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

After determining the rating and allowed error, you need to proceed to determining the voltage value. It is designated by numbers together with letters such as V, VDC, WV or VDCW. The designation WV stands for operating voltage. The numbers indicate the maximum permitted 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 capacitors operating on alternating voltage cannot be used in constant voltage circuits, and vice versa.

To determine the polarity of the terminals, “+” and “–” signs are marked on the case. If they are not there, then the capacitor is connected to the circuit on either side.

Digital transcript

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

The third digit is a multiplier of zero. Therefore, decryption is performed according to 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 the limit of 0-6, for example, it costs 8, then the first digit should be multiplied by 0.01. Thus, the cipher 378 means 0.37. When there is a 9 at the end, the combination of the first two digits is multiplied by 0.1. The designation 379 should be read as 3.7.

When everything is clear from the combination of numbers and 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 cipher 4R1 reads 4.1 pF. If the marking contains the letters p, n or u, then they should also be replaced with a comma. For example, n61 means 0.61 nanofarads.

Mixed marking

This code on the capacitor body includes letters and numbers, alternating with each other. This is usually applied according to the “letter - number - letter” pattern. The first letter indicates the operating temperature of the reliable condition of the capacitor. The second number is the permissible temperature limit.

The third letter means a change in capacity from the minimum temperature to the maximum permissible temperature. If there is a letter “A”, then this is an accurate indicator. Its error is 0.1%. If there is a letter “V”, the capacity indicator ranges from 22% to 82%. It is very common to find capacitors with the letter “R”, which means a 15% deviation of the capacitance from temperature changes.

Changing parameters during operation

To understand which capacitors are good and which are not, you need to know the general characteristics and remember how the parameters depend on each other. For example, the ability of the unit to emit gases in operating mode requires, when installing the circuit, to create a reserve of permissible 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 temperatures.

When using a capacitor in variable current circuits, the dependence on the operating frequency must be taken into account. Typically, the operating frequency of the varying voltage should not deviate from 50 Hz. For higher frequencies, capacitors with a lower permissible voltage must be included. Otherwise, the dielectric will become very hot, which will lead to rupture of the housing.

Elements with high capacity and low leakage currents are able to retain 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 serve to store electrical energy. Without them, not a single radio or television receiver circuit will function. The advent of microcircuits changed the function of capacitors. Many of them are manufactured in an integrated form.

Video

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, therefore 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.
On this picture:

1. Paper;
2. Foil;
3. Glass insulator;
4. Lid;
5. Frame;
6. Cardboard gasket;
7. Wrapping;
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 load size. 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.

A capacitor is found in Master Kits (and in electronic devices in general) almost as often as a resistor. Therefore, it is important to at least in general outline its main characteristics and operating principle.

Operating principle of a capacitor

In its simplest form, the design consists of two plate-shaped electrodes (called plates) separated by a dielectric whose thickness is small compared to the size of the plates. The greater the ratio of the area of ​​the plates to the thickness of the dielectric, the higher the capacitance of the capacitor. To avoid physically increasing the size of the capacitor to enormous sizes, capacitors are made multilayer: for example, strips of plates and dielectrics are rolled into a roll.
Since any capacitor has a dielectric, it is not capable of conducting direct current, but it can store an electric charge applied to its plates and release it at the right time. This is an important property

Let's agree: we call a radio component a capacitor, and its physical quantity - a capacitance. That is, it is correct to say: “the capacitor has a capacity of 1 μF,” but it is incorrect to say: “replace that capacitor on the board.” Of course, they will understand you, but it is better to follow the “rules of good manners.”

The electrical capacitance of a capacitor is its main parameter
The larger the capacitor's capacity, the more charge it can store. The electrical capacitance of a capacitor is measured in Farads and is designated F.
1 Farad is a very large capacity (the globe has a capacity of less than 1F), therefore, to designate capacity in amateur radio practice, the following basic dimensional values ​​are used - prefixes: µ (micro), n (nano) and p (pico):
1 microFarad is 10-6 (one part per million), i.e. 1000000µF = 1F
1 nanoFarad is 10-9 (one part in a billion), i.e. 1000nF = 1µF
p (pico) - 10-12 (one trillionth part), i.e. 1000pF = 1nF

Like Om, Farad is the name of a physicist. Therefore, as cultured people, we write the capital letter “F”: 10 pF, 33 nF, 470 µF.

Capacitor Rated Voltage
The distance between the plates of a capacitor (especially a large-capacity capacitor) is very small, reaching units of a micrometer. If too high a voltage is applied to the capacitor plates, the dielectric layer may be damaged. Therefore, each capacitor has such a parameter as a rated voltage. During operation, the voltage on the capacitor should not exceed the rated voltage. But it is better when the rated voltage of the capacitor is slightly higher than the voltage in the circuit. That is, for example, in a circuit with a voltage of 16V, capacitors with a rated voltage of 16V (in extreme cases), 25V, 50V and higher can work. But you cannot install a capacitor with a rated voltage of 10V in this circuit. The capacitor can fail, and this often happens with an unpleasant bang and the release of acrid smoke.
As a rule, amateur radio designs for beginners do not use a supply voltage higher than 12V, and modern capacitors most often have a rated voltage of 16V or higher. But remembering the voltage rating of the capacitor is very important.

Types of capacitors
Many volumes could be written about various capacitors. However, this has already been done by some other authors, so I will tell you only the most necessary: ​​capacitors can be non-polar and polar (electrolytic).

Non-polar capacitors
Non-polar capacitors (depending on the type of dielectric are divided into paper, ceramic, mica...) can be installed in the circuit in any way - in this they are similar to resistors.
As a rule, non-polar capacitors have a relatively small capacitance: up to 1 µF.

Marking of non-polar capacitors
A three-digit code is applied to the capacitor body. The first two digits determine the capacitance value in picofarads (pF), and the third - the number of zeros. So, in the figure below, code 103 is applied to the capacitor. Let’s determine its capacity:
10 pF + (3 zeros) = 10000 pF = 10 nF = 0.01 µF.

Capacitors with a capacity of up to 10 pF are marked in a special way: the symbol “R” in their coding represents a comma. Now you can determine the capacitance of any capacitor. The table below will help you check yourself.

As a rule, in amateur radio designs it is permissible to replace some capacitors with similar ones in nominal value. For example, instead of a 15 nF capacitor, the kit can be equipped with a 10 nF or 22 nF capacitor, and this will not affect the operation of the finished design.
Ceramic capacitors have no polarity and can be installed in any position of the terminals.
Some multimeters (except for the most budget ones) have a function for measuring the capacitance of capacitors, and you can use this method.

Polar (electrolytic) capacitors
There are two ways to increase the capacitance of a capacitor: either increase the size of its plates, or reduce the thickness of the dielectric.
To minimize the dielectric thickness, high-capacity capacitors (above several microfarads) use a special dielectric in the form of an oxide film. This dielectric works normally only if the voltage is correctly applied to the capacitor plates. If the polarity of the voltage is reversed, the electrolytic capacitor may fail. The polarity mark is always marked on the capacitor body. This can be either a “+” sign, but most often in modern capacitors the “minus” terminal is marked with a stripe on the body. Another, auxiliary way to determine polarity: the positive terminal of the capacitor is longer, but you can focus on this sign only before the terminals of the radio component are cut off.
The PCB also has a polarity mark (usually a “+” sign). Therefore, when installing an electrolytic capacitor, be sure to match the polarity marks on both the part and the printed circuit board.
As a rule, in amateur radio designs it is permissible to replace some capacitors with similar ones in nominal value. It is also permissible to replace the capacitor with a similar one with a higher permissible operating voltage. For example, instead of a 330 µF 25V capacitor kit, you can use a 470 µF 50V capacitor, and this will not affect the operation of the finished design.

Appearance of an electrolytic capacitor(capacitor installed correctly on the board)

According to another version (as we know, the plausibility of historical facts of very high frequencies is quite difficult to prove), Muschenbroek specifically tried to “charge” the water in the jar. At that time, scientists and researchers still believed that electricity was a kind of liquid that was found in any charged body or object. So, the scientist deliberately lowered the electrode of the electric machine into the water, and then, taking the jar with one hand and accidentally touching the electrode with the other, he again felt a powerful electric shock. And since the experiment was carried out in the city of Leiden, this jar, a prototype of a capacitor, began to be called the Leiden jar.

There is another version of the event. Around the same time - in 1745 rector of the cathedral in Pomerania - German clergyman Ewald Jugen von Kleist tried to conduct a scientific experiment in order to “charge” holy water with electricity and thereby make it even more useful. He also used an electric machine, which were quite popular at the time. True, he did not put the electrode itself into the jar, but used a metal nail as a conductor. Having accidentally touched a nail, I also felt the full force of electricity.

In this form, the capacitor existed for the following 200 years. Scientists and researchers modified it a little - they coated the jar inside and out with metal, removed the water, and used it for various experiments in the field of studying electricity.

By the way, the word “capacitance”, which is now used to denote the value of modern capacitors, is a tribute to the past. After all, initially this element was a glass vessel (jar), which had a certain volume or capacity. By the way, Leyden jars were of different volumes and the larger, the more area the electrodes covered them from the inside and outside. , as is known, even from a school physics course, the larger the area of ​​the capacitor’s electrodes, the greater its capacity.