Types of capacitors, their characteristics and purpose
The accumulation and conversion of electrical energy can be attributed to the basic tasks that solve auxiliary elements of radio equipment. A capacitor is a passive component and acts as a kind of capacity for the incoming charge. The design of standard devices provides for plate electrodes that are separated by thin dielectrics. More complex types of capacitors may contain several electrode layers forming cylindrical winding. There are other distinctive signs that determine the possibility of using elements for a particular equipment.
To date, there is hardly any area of radio engineering in which these devices would not be used. The most common combinations of capacitors with resistors and inductors involved in the construction of electrical circuits.Such nodes support the functions of frequency filters, oscillatory circuits and feedback lines. Another common problem is the smoothing of voltage ripples required in secondary power sources. In laser systems, flash systems and magnetic accelerators, an electric capacitor is used to deliver a one-time charge with a large power rating. And on the contrary, electrical devices are equipped with these elements in order to compensate for reactive power energy. Although such elements cannot be considered as full-fledged capacitive energy storage devices, in some systems they also act as information carriers.
For the visual determination of the belonging of a capacitor to one category or another, special symbols are used. The first indication is the capacitive potential expressed by microfarads (μF). Other units of measurement may be used, which will also be indicated by the corresponding marking. The type of material used in the construction is not always indicated - as a rule, non-marking ceramic and film non-polar models are produced.In turn, the designation of tantalum capacitors corresponds to resistors - except for the presence of the µ sign and the numbers 104 or 107. Such devices may be orange, yellow or black. The sign marking also indicates dimensional parameters and capacity. High-voltage and electrolytic models are labeled with the maximum voltage value, and for variable capacitors the capacitance range is indicated.
The main working parameter is the capacity on which the ability of a particular model to accumulate charge depends. It is necessary to separate the nominal and actual capacity, since in practice using the second value may be less. The range of values by volume can vary from 1 to 50 microfarads, and in some cases, the maximum reaches 10,000 microfarads. An important indicator of energy density, largely determined by the design of the product. The largest density is characterized by large-format types of capacitors, in which the mass of the plate with electrolyte significantly exceeds the weight of the case. For example, with a capacity of 10,000 μF with a voltage of 0.45 kW and a mass of about 2 kg, the density can reach 600-800 J / kg. Just such a model is beneficial to use for long-term storage of energy.In addition, the working properties of capacitors are determined by the tolerance. It is just about the error in the ratio of real and nominal capacity. This value is expressed as a percentage and averages 20-30%. In some areas of radio engineering products are used with a 1% tolerance.
These are devices based on disk ceramic elements with barium titanate dielectrics. Such a capacitor can be used in systems with voltages up to 50,000 V, but it is important to take into account that it has minimal temperature stability and a wide range of capacitance changes. Among the advantages can be noted a small leakage current, modest size (with a large capacity charge) and the ability to operate at high frequency. As for the purpose, ceramic capacitors are used in circuits with pulsating, alternating and direct current. Most often use models with a capacity up to 0,5 microfarad. In the process, a capacitor of this type copes well with external loads, including mechanical shocks. It cannot be said that the ceramic case is distinguished by a long operational life and durability, however, it maintains its technical properties in the stated period.
In the diagrams, devices of this type are indicated by the marking K73-17 or CL21. Their shell is formed by a metallized film, and epoxy compound is used for the body. Just the presence of this filler in the design makes polyester capacitors resistant to temperature, physical and chemical influences. This set of performance characteristics led to the wide distribution of K73-17 capacitors in the production of lighting devices. The average capacity of the device is 15 µF at a maximum voltage of about 1500 V. The characteristics are modest, but this does not prevent the use of a capacitor in the same pulsed and alternating current circuits. In addition, the low cost of the device contributes to its popularity in the radio market.
Polypropylene based condenser
It is also a variant of a relatively inexpensive electric charge drive, which at the same time has a low loss coefficient and high dielectric strength. The advantages include optimal hygroscopicity. That is, one of the main enemies of radio elements in the form of moisture in polypropylene capacitors is not terrible.Metallized film or foil strips are used as insulators. In the newest versions, the technology of a self-repairing shell is also used, which increases the reliability and durability of the capacitor.
The device can operate at higher frequencies while maintaining sufficient power. This quality allows the use of condensers in induction heating systems, supplemented by water cooling. The use of such elements in the equipment of 220 V electric motors is also common. In this case, they act as starting components. This function is best implemented by models with a working capacity in the range of 1-100 microfarads and a voltage of 440 V. But these are not the only synthetic-based drives. What are thermoplastic capacitors? Polysulfone and polycarbonate elements deserve attention. The first ones are characterized by low moisture absorption and the ability to maintain high voltage at temperature drops, and the second ones in the process demonstrate optimal electrical stability.
The basis of the device is formed by tantalum pentoxide with oxide electrolytic filling.The condenser has a high capacity-to-volume ratio, a wide range of supported temperatures and compactness. Such components are used in small-scale instrument making, computers and other computing equipment. The following types of capacitors can be distinguished in this family: polar and non-polar, solid-state, and liquid. The most attractive in terms of performance qualities are solid-state devices, since they are characterized by the ability to maintain high voltage. However, under conditions of critical excess of the permissible current value, they can fail. The capacity of tantalum models is 1000 microfarads, but compared to electrolytic counterparts, their own inductance is much lower, which allows the element to be used at high frequencies.
Features of high-voltage models
Elements of this type can be used in systems with high voltages, reaching 15,000 V. In this case, the capacitance of high-voltage capacitors is small - about 50-100 nF. Ceramic is more commonly used as a dielectric material.Due to this basis, high stress loads are maintained, and the body protects the filling from plate breakdowns.
Glass vacuum products are also common, which also support voltages of more than 10,000 V. They are flasks with concentric electrodes that provide small frequency losses in the process. Apply high-voltage capacitors of this type to solve critical radio frequency problems with inductive heating. But these components are more expensive, fragile and large in size.
Multi-layer and single-layer structures
Usually this classification is applied to capacitors made of ceramics. So, single-layer capacitors (disk) have a simple device, but this does not affect the reduction in size. In most cases, they are more massive than multi-layered counterparts. As a result, the capacity of the device increases, but large sizes still limit their distribution in certain areas.
As for the multilayer elements, they are generally similar in performance to disk ones, but the potential of the drives is even higher.Also a significant advantage lies in reliability and durability. The form factor in which multilayer capacitors are performed makes them less sensitive to aggressive media, which expands the scope of application. Such components are mainly used in expensive professional equipment.
Impregnated oil capacitors
This is a separate group of radio elements, which are based on paper fillers. They are treated with special solutions like wax and epoxy resins. What are oil type capacitors? Fundamentally different models for direct and alternating current. The former are used for frequency filtering, voltage boosting and elimination of the electric arc. Condensers on oil impregnation for systems with alternating current used in industry. Such a device has a large capacity and can handle large peak loads. As a rule, it is used as a starting component for electric motors. Additional features include phase separation, power correction and voltage equalization.
Negative factors for capacitor use
One of the main problems with the use of capacitors is the high likelihood of an explosion due to overheating, which occurs due to large leaks. Also increase the risk of breakage of the element may be located radiators with high thermal radiation. What types of capacitors are most susceptible to explosions? Most often this happens with electrolytic devices provided with unreliable enclosures. Optimization of the design in order to reduce the size of the product forces manufacturers to use thin shells, so there may be scattering of parts of the capacitor and spraying of the electrolyte with strong overheating or under conditions of increased internal pressure.
Both the simplest single-layer and multi-layer high-voltage models of capacitors perform important tasks for radio equipment. At a minimum, they adjust the current parameters, which, with similar dimensions, cannot be provided by any other technical component. At the same time, an electric capacitor is not at all the ideal solution, which causes a constant search for new formats of its execution.Manufacturers of sophisticated equipment are experimenting with designs, fillers, and physical properties, trying to offer the optimum consumer qualities of this device. Among the most important target parameters in this regard are capacitor resistance to loads, wide operating ranges, minimal radiative forcing and high service life.