Electrical capacitors are widely used in electronic equipment. They lead in the number of applications in hardware units and by some criteria are inferior only to resistors. Capacitors are present in any electronic device and their need for modern electronics is constantly growing. Along with the existing wide nomenclature, the development of new types that have improved electrical and operational characteristics continues.
- 1 What is a capacitor?
- 2 Groups by dielectric type
- 3 Legend
- 4 Selection of nominal
- 5 Parallel capacitor connection
- 6 Consistently connecting capacitors
What is a capacitor?
A capacitor is an element of an electrical circuit, which consists of conductive electrodes, isolated from each other by a dielectric.
Capacitors are distinguished by their capacity, namely, the ratio of charge to potential difference, which is transmitted by this charge.
In the SI international system Capacity of a capacitor is taken as a unit of capacity. with an increase in potential by one volt with a single pendant charge message. This unit is called the farada. It is too large to be used for practical purposes. Therefore, it is customary to use smaller units of measure, such as picofarad (pF), nanofarad (nF) and microfarad (μF).
Groups by dielectric type
Dielectrics are used to insulate the plates from each other. They are made from organic and inorganic materials. Often, oxide films of metals are used as dielectric.
By type of dielectric elements are divided into groups:
Elements with an organic dielectric are made by winding thin strips of special paper or film. Also used combined dielectric with foil or metallized electrodes. Such elements can be both high-voltage (over 1600 V) and low-voltage (up to 1600 V).
Ceramic, mica, glass and glass-ceramic, glass enamel are used in products with inorganic dielectric. Their plates consist of a thin layer of metal that is deposited on the dielectric by metallization. There are high-voltage, low-voltage and interference suppression.
Compressed gas (freon, nitrogen, gas), air or vacuum is used as a dielectric gas. By the nature of the capacity change and the function performed, such elements are constant and variable.
The most widely used elements with a vacuum dielectric. They have large specific capacitances (as compared to gaseous dielectric) and higher electrical strength. Elements with vacuum dielectric have stable parameters with temperature changes in the environment.
Scope - transmitting devices operating on short, medium and long wave bands with a frequency of up to 30-80 MHz.
Elements with an oxide dielectric are:
- general purpose;
- high frequency;
The dielectric is an oxide layer, which is deposited on the anode by electrochemical means.
Elements are designated on the reduced and full system.
With a reduced system letters and numbers are putwhere the letter denotes a subclass, a digit denotes a group depending on the dielectric used. The third item indicates the item type registration number.
With a full symbol, the parameters and characteristics are indicated in the following sequence:
- symbol designation of the product;
- rated voltage of the product;
- nominal capacity of the product;
- capacity tolerance;
- temperature stability of the product capacity;
- nominal reactive power of the product.
Selection of nominal
Capacitors can be connected to each other in various ways.
In practice, there are often situations when installing a circuit or replacing a defective item, you have to use a limited number of radio components. It is not always possible to choose the elements of the desired denomination.
In this case, it is necessary to apply a series and parallel connection of capacitors.
Parallel capacitor connection
With parallel wiring, their the total value will be the sum of the capacities individual items. With this wiring diagram, all element covers are connected in groups. One of the findings of each element is connected to one group, and the other output to another group.
Wherein voltage on all plates will be the same, because all groups are connected to the same power source. In fact, one capacity is obtained, the total value of all capacities in a given circuit.
To get a large capacity, use a parallel connection capacitor.
For example, you need to connect engine with three phases to a single-phase network of 220 V. For operating mode engine a capacitance of 135 μF is required. It is very difficult to find, but can be obtained by applying a parallel connection of elements at 5, 30 and 100 microfarads. As a result of the addition, we obtain the necessary unit of 135 μF.
Consistently connecting capacitors
A series connection of capacitors is used if it is necessary to obtain a capacitance smaller than the capacitance of the element. Such elements withstand higher voltages. When the capacitors are connected in series, the reciprocal of the total capacitance is equal to the sum of the reciprocals of the individual elements. To obtain the required value, certain capacitors are needed, the series connection of which will give the required value.
When capacitors are connected in series, each of its outputs is connected to one output of another element. It turns out a kind of chain of series-connected capacitors, where the extreme terminals are connected to the power source.
The capacity of a common battery is always less than the minimum capacity of the elements included in it. That is, half of the capacity of each of these containers.
When the capacitors are connected in series, the distance between the plates of the elements increases.
For example, with the series connection of two 200-volt elements, it can be safely included in the circuit with voltage up to 1000 V.
This connection method much less used, because the capacity of such size and operating voltage can be purchased in stores.
Thus, knowing the principle of the general calculation of parallel and serial connection capacitors, you can always get out of a predicament, having at hand a limited number of denominations.