Useful materials. Types of capacitors, their characteristics and purpose

Many people are interested in whether capacitors have types? There are many capacitors in electronics. Indicators such as capacitance, operating voltage and tolerance are the main ones. The type of dielectric from which they are composed is no less important. This article will look in more detail at what types of capacitors are based on the type of dielectric.

Classifications of capacitors.

Capacitors are common components in radio electronics. They are classified according to many indicators. It is important to know which models, depending on the nature of the change in value, represent different capacitors. Capacitor types:

1. Devices with constant capacity.
2. Devices with variable capacity.
3. Construction models.

The type of dielectric of the capacitor can be different:

Paper;
- metal paper;
- mica; Teflon;
- polycarbonate;
- electrolyte.

According to the installation method, these devices are intended for printed and wall-mounted installation. In this case, the types of SMD capacitor housings are:

Ceramic;
- plastic;
- metal (aluminum).

You should be aware that devices made of ceramics, films and non-polar types are not marked. Their capacitance indicator ranges from 1 pF to 10 µF. And electrolyte types are shaped like barrels in an aluminum housing and are marked. The tantalum type is produced in rectangular-shaped cases. These devices come in different sizes and colors: black, yellow and orange. They also have code markings.

Electrolytic capacitors made of aluminum.

The basis of aluminum electrolytic capacitors is two thin twisted aluminum strips. Between them is paper containing electrolyte. The capacity indicator of this device is 0.1-100,000 uF. By the way, this is its main advantage over other types. The maximum voltage is 500 V.

The disadvantages include increased current leakage and a decrease in capacitance with increasing frequency. Therefore, boards often use a ceramic capacitor along with an electrolytic capacitor.

It should also be noted that this type differs in polarity. This means that the negative terminal of the device is at a negative voltage, unlike the opposite terminal. If you do not adhere to this rule, then most likely the device will fail. Therefore, it is recommended to use it in circuits with direct or pulsating current, but in no case alternating current.

Electrolytic capacitors: types and purpose.

There is a wide range of types of electrolytic capacitors. They are:

Polymer;
- polymer radial;
- with low current leakage;
- standard configuration;
- with a wide temperature range;
- miniature;
- non-polar;
- with a hard output;
- low impedance.

Source:

Where are electrolytic capacitors used? Types of aluminum capacitors are used in various radio devices, computer parts, peripheral devices such as printers, graphics devices and scanners. They are also used in construction equipment, industrial measuring instruments, weapons and space.

Capacitors KM

There are also clay capacitors of the KM type. They are used:
- in industrial equipment;
- when creating measuring instruments characterized by high-precision indicators;
- in radio electronics;
- in the military industry.

Devices of this type are characterized by a high level of stability. The basis of their functionality is pulse modes in circuits with alternating and constant current. They are characterized by a high level of adhesion of ceramic linings and long service life. This is ensured by the low value of the coefficient of capacitive temperature variability.

KM capacitors, with their small sizes, have a high capacitance value, reaching 2.2 μF. The change in its value in the operating temperature range for this type ranges from 10 to 90%.

Types of ceramic capacitors of group H, as a rule, are used as adapters or blocking devices, etc. Modern clay devices are made by pressing under pressure into a single block of the thinnest metallized ceramic plates.

The high level of strength of this material makes it possible to use thin workpieces. As a result, the capacitance of the capacitor, proportional to the volume indicator, increases sharply.

KM devices are highly expensive. This is explained by the fact that precious metals and their alloys are used in their manufacture: Ag, Pl, Pd. Palladium is present in all models.

Ceramic capacitors.

The disk model has a high level of capacity. Its value ranges from 1 pF to 220 nF, and the highest operating voltage should not be higher than 50 V.

The advantages of this type include:

Low current losses;
- small size;
- low induction rate;
- ability to function at high frequencies;
- high level of temperature stability of the container;
- ability to work in circuits with direct, alternating and pulsating current.

The basis of the multilayer device is made up of alternating thin layers of ceramic and metal.

This type is similar to a single-layer disc. But such devices have a high capacity. The maximum operating voltage is not indicated on the housing of these devices. Just like on the single-layer model, the voltage should not be higher than 50 V.

The devices operate in circuits with direct, alternating and pulsating current.

The advantage of high-voltage ceramic capacitors is their ability to function at high voltage levels. The operating voltage range ranges from 50 to 15000 V, and the capacitance value can range from 68 to 150 pF.

They can operate in circuits with direct, alternating and pulsating current.

Tantalum devices.

Modern tantalum devices are an independent subtype of the electrolytic type made of aluminum. The basis of capacitors is tantalum pentoxide.

Capacitors have a low voltage rating and are used when it is necessary to use a device with a large capacitance rating, but in a small case. This type has its own characteristics:

Small size;
- the maximum operating voltage is up to 100 V;
- increased level of reliability during long-term use;
- low current leakage rate; wide range of operating temperatures;
- the capacitance indicator can vary from 47 nF to 1000 uF;
- devices have a lower level of inductance and are used in high-frequency configurations.

The disadvantage of this type is its high sensitivity to increased operating voltage.

It should be noted that, unlike the electrolytic type, the positive terminal is marked with a line on the body.

Types of cases.

What types of tantalum capacitors are there? Types of tantalum capacitors are distinguished depending on the housing material.

1. SMD housing. To make packaged devices that are used in surface mount applications, the cathode is connected to the terminal using a silver-filled epoxy resin. The anode is welded to the electrode, and the stringer is cut off. After the device is formed, printed markings are applied to it. It contains an indicator of the nominal voltage capacitance.

2. When forming this type of housing device, the anode conductor must be welded to the anode terminal itself and then cut off from the stringer. In this case, the cathode terminal is soldered to the base of the capacitor. Next, the capacitor is filled with epoxy and dried. As in the first case, markings are applied to it.

Capacitors of the first type are more reliable. But all types of tantalum capacitors can be used:

In mechanical engineering;
- computers and computer technology;
- equipment for television broadcasting;
- electrical appliances for household use;
- various power supplies for motherboards, processors, etc.

Search for new solutions.

Today, tantalum capacitors are the most popular. Modern manufacturers are looking for new methods to increase the strength of a product, optimize its technical characteristics, as well as significantly reduce prices and unify the production process.

To this end, attempts are made to reduce costs on a component-by-component basis. Subsequent robotization of the entire production process also contributes to a drop in the price of the product.

An important issue is also reducing the body of the device while maintaining high technical parameters. Experiments are already being carried out on new types of enclosures in a smaller version.

Polyester capacitors.

The capacitance indicator of this type of device can range from 1 nF to 15 uF. The operating voltage range is from 50 to 1500 V.

There are devices with different degrees of tolerance (capacitance tolerance is 5%, 10% and 20%).

This type has temperature stability, high capacity and low cost, which explains their widespread use.

Capacitors with variable capacitance.

Types of variable capacitors have a certain operating principle, which consists in accumulating charge on electrode plates insulated by a dielectric. These plates are distinguished by their mobility. They can move.

The moving plate is called the rotor, and the stationary plate is called the stator. When their position changes, the intersection area and, as a consequence, the capacitance indicator of the capacitor will also change.

Capacitors come in two types of dielectrics: air and solid.

In the first case, ordinary air acts as a dielectric. In the second case, ceramics, mica and other materials are used. To increase the capacity of the device, the stator and rotor plates are assembled into blocks mounted on a single axis.

Capacitors with an air dielectric type are used in systems with constant capacitance adjustment (for example, in radio receiver tuning units). This type of device has a higher level of durability than ceramic.

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 a resistance, the value of which decreases with increasing frequency.

Like resistors, capacitors They 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.

Capacitors constant capacity. The conventional graphic designation of a constant-capacity capacitor - two parallel lines - symbolizes its main parts: two plates and a dielectric between them. Near the capacitor designation on the diagram, its rated capacitance and sometimes its rated voltage are usually indicated. The basic unit of measurement 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.

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.

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

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). In this case, the capacitance from 0 to 100 pF is denoted 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 designated in nofarads, 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 unit of measurement is placed in place of zero and comma (180 pF = 0.18 nF-N18; 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 - in place of 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 - YuN, 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.

Losses in capacitors, determined mainly by losses in the dielectric, increase with increasing temperature, humidity and frequency. Have the least losses capacitors with a dielectric made of high-frequency ceramics, with mica and film dielectrics, the largest - capacitors with paper dielectric and ferroelectric ceramics. 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 characterized by a different temperature coefficient of capacity (TKE), which shows the relative change in capacity with a change in temperature by one degree; TKE can be positive or negative. According to 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 settings of oscillatory circuits when operating over a wide temperature range, series and parallel connections are often used capacitors, for 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 longer and thinner the leads, the larger it is. capacitor, the larger the dimensions of its plates and internal connecting conductors.

Paper materials have the highest inductance 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 work well at frequencies above a few megahertz. Therefore, in practice, to ensure the operation of the locking capacitor in a wide frequency range, connect ceramic or mica in parallel with paper capacitor small container.

However, there are paper capacitors and 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 shifting the strips (coverings) to opposite ends of the roll and soldering them

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-throughs are used capacitors. Such capacitor has three terminals, two of which are a solid current-carrying rod passing through the capacitor body. One of the plates is attached to this rod capacitor. The third terminal is a metal body to which the second plate is connected. Passage housing capacitor 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. At high frequencies, ceramic feedthroughs are used 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.

For the same purpose as pass-throughs, supporting ones are used. capacitors, which are a kind of mounting racks mounted on a metal chassis. The lining connected to it is distinguished in the designation of such capacitor three slanted lines symbolizing “grounding”

To operate in the audio frequency range, as well as to filter rectified supply voltages, you need capacitors, the capacity of which is measured in tens, hundreds and even thousands of microfarads. Oxide compounds have such a capacity at fairly small sizes. 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 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 a metal case. capacitor. Unlike others, most types of oxide capacitors 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 meet this condition results in an exit capacitor out of order, which is sometimes accompanied by a powerful explosion.

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

In order to reduce the size, two are sometimes enclosed in one body capacitor, but only three conclusions are drawn (one is general).

Capacitors variable capacity (VCA). Capacitor variable capacitance 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. The dielectric in KPE is most often air. 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.

The main parameters of the KPI, which allow us to evaluate its capabilities when operating in an oscillating 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.

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

Trimmers capacitors. To set the initial capacitance of the oscillatory circuit, which determines the maximum frequency of its tuning, trimmers are used capacitors, the capacity of which can be changed from units of 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. Trimmer axes capacitors(usually short) have a slot, so adjusting their capacity is only possible with the use of a tool (screwdriver). Most widely used in broadcasting equipment capacitors with a solid dielectric.

Design of ceramic trimmer capacitor(PDA) is one of the most common. It consists of a ceramic base (stator) and a ceramic disk (rotor) movably mounted on it. Covers capacitor- thin layers of silver - applied by burning onto the stator and the outer side of the rotor. The capacity is changed by rotating the rotor. In the simplest equipment, wire trimmers are sometimes used. capacitors. 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. 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.).

Self-regulating capacitors. Using special ceramics as a dielectric, the dielectric constant of which strongly depends on the electric field strength, it is possible to obtain capacitor, the capacitance of which depends on the voltage on its plates. Such capacitors are called variconds (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.

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

Symbol for variconda - symbol capacitor with the sign of nonlinear self-regulation and the Latin letter U.

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°.

Permissible deviation of the capacity of any capacitor from the nominal value is usually indicated as a percentage, but on capacitors of very small capacities the permissible deviation from the nominal value is indicated in picofarads. If on capacitor“100 ± 10%” is indicated, this means that its capacity cannot be less than 90 or more than 110 pF. If the tolerance is not indicated in the marking, then such capacitor permissible deviation from the nominal value ±20%. On capacitors, manufactured with only one, certain permissible deviation from the nominal value, for example, oxide (old name - electrolytic) capacitors of the KE series, ferroelectric ceramic KDS, the tolerance is also not indicated.

However, it should be borne in mind that the voltage margin should not be too high, since capacitors with a higher rated voltage, the dimensions are usually larger, which leads to an increase in the dimensions of the entire device as a whole, and ultimately to an increase in the cost of the device.

Oxide capacitors(or as they were previously called - electrolytic) are not recommended for use at AC voltages close to half the operating voltage capacitor. This is explained by the features of the device and their mode of operation.

At normal temperature, the actual capacity of the oxide capacitor may be 20% less and 80% more than indicated on its body. At the maximum operating temperature, which for capacitor widely used is 70 - 80°C, the capacity can increase by 20 - 30% compared to that measured at normal temperature. U capacitors intended for household equipment, the capacity at a temperature of - 10 ° C can be halved compared to the capacity at normal temperature ( capacitors K50-6, K50-7). In equipment for field, working conditions are used capacitors(K50-3, K50-ZA, K50-ZB), in which the capacity is reduced by no more than half at a temperature of - 40 ... - 60 ° C.

Oxide capacitors polar. They work well in DC and pulsating voltage circuits. At the same time, non-polar oxide ones are also produced. capacitors with aluminum and tantalum foil electrodes. Such capacitors can operate in alternating current circuits.

Rated voltages of industrially produced oxide capacitors range from 3 to 450 V, and capacitance ratings range from fractions of a microfarad to several thousand microfarads, with capacitors with larger capacitances typically having lower voltage ratings.

Since the maximum permissible voltage also includes the amplitude of the alternating component, then for polar oxide capacitors with an operating voltage of 100 - 450 V, the value of the variable component should not exceed 8% of these voltages. The larger the capacitance and rated voltage, the smaller the permissible amplitude of the alternating current. If the variable component is large, the oxide capacitor overheats. In such cases, oxide capacitors should be replaced with other types of capacitors, for example, high-capacity paper capacitors.

To the features of oxide capacitors It also applies that in rectifier filters they can only be used at frequencies up to 1000 Hz. As the frequency increases (above 50 Hz), their effective capacitance will become smaller and smaller in relation to the nominal one. At higher frequencies, the permissible amplitude of the variable component also decreases in inverse proportion to the frequency. So, at a frequency of 100 Hz, the permissible amplitude is half that at a frequency of 50 Hz.

Oxide capacitors have a relatively low insulation resistance. At nominal for this type capacitors operating voltage, the leakage current can reach up to 0.1 mA for each microfarad of capacitance. Leakage above this norm indicates poor quality capacitor. Such capacitor needs to be replaced.

Oxide capacitors They are used primarily in power supply filters, in decoupling filters, and in transistor equipment - in communication circuits between transistor stages and for shunting resistors in transistor emitter circuits.

As with other radio components, the requirements for the rigidity of permissible deviations of capacitance from the nominal value are determined for capacitors depending on what function they perform in one or another device. Yes, for capacitors shunting resistors in the cathode circuits of RF and IF amplifier lamps, capacitors filter and blocking in the anode and screen circuits, the capacitances can be as large as desired, but not less than the nominal value indicated in the diagram; for coupling capacitors used in low-frequency amplifiers, deviations from the nominal value can be 20 - 30%. Capacity capacitors, used in correction circuits that improve the frequency response of low-frequency amplifiers, should not differ by more than ±10% from the calculated value.

Type of dielectric used in capacitor, plays a decisive role in determining the scope of application capacitor. In oscillatory circuits of the long and medium wave range, one can practically use capacitors of various types, including those with a mica dielectric, although such capacitors do not always have sufficiently small losses.

Ceramic materials can be used in all high-frequency current circuits. capacitors(for capacitances up to 1000 - 5000 pF) or non-inductive paper (for capacitances more than 1000 - 5000 pF).

In circuits of shielding grids of lamps and in anode filters of high-frequency cascades, it is permissible to use non-induction paper to decouple circuits. capacitors; in this case, the outer lining must be grounded or connected to the common negative wire capacitor(this terminal is marked with the corresponding sign on the body or end of the non-inductive capacitors). In low-frequency stages everything capacitors may be paper.

Capacitors It is advisable to have variable capacitance for adjusting the oscillatory circuit of receivers with an air dielectric. This applies to an even greater extent to the oscillatory circuits of measuring instruments. From the tuning capacitors The best are capacitors with air and ceramic dielectrics.

Basic faults capacitors: insulation breakdown (short circuit between plates), high leakage current (poor insulation between plates), breakage of leads, and for oxide (electrolytic) leads - loss of capacity.

Functionality check capacitors. Malfunctions capacitors, especially large capacitance, such as loss of capacitance, short circuit and large leakage current, can be easily detected using a megohmmeter, as well as an ohmmeter or even a simple probe.

If capacitor of a large capacity is in working order, then when a probe is connected to it, the arrow of the device will first deviate sharply to the right, and the greater the capacity, the greater the deviation will be. capacitor, and then relatively slowly begins to return to the left and settles above one of the divisions at the beginning of the scale. If capacitor is faulty, that is, it has lost capacity or has a leak, then in the first case the needle of the device will not deviate to the right at all, and in the second case it will deviate almost the entire scale, and then settle on one of the divisions at the end of it, depending on the value of the leakage resistance. When checking a capacitor in this way, you should always pay attention to whether the supply voltage of the device exceeds the permissible voltage capacitor, otherwise in capacitor Insulation breakdown may occur during testing.

The insulation state of capacitors with a capacity of the order of microfarads, and sometimes even tenths of a microfarad, can also be assessed by the intensity of the spark, if capacitor connect first to a voltage source and charge, and then short-circuit its terminals. In this way you can check capacitors any types (except electrolytic).

In some cases it is difficult to verify capacitors small capacitance (of the order of tens and hundreds of picofarads), in which the spark during discharge is insignificant, and the leakage resistance is so high that capacitor with a broken output can easily be mistaken for a completely serviceable one with a high leakage resistance.

Using an ohmmeter or avometer in resistance measurement mode, if necessary, you can determine the polarity of an oxide capacitor (type K50-6, etc.). When connected to capacitor device c. Depending on how the probes are connected, it will show more resistance in one position and less resistance in another. The higher resistance corresponds to the case when the positive probe of the device is connected to the positive pole capacitor.

Oxide (electrolytic) capacitors, having polar terminals, can also be connected in parallel and in series. However, when connecting them in series, additional measures should always be taken to prevent insulation breakdown. This is especially important when, in the absence of oxide capacitors they are replaced with the required operating voltages capacitors less operating voltage. To equalize the voltages, resistors of the same resistance (0.5 - 1.5 MOhm) are connected in parallel to each of the series-connected capacitors. The losses caused by connecting such resistors are insignificant and practically do not affect the operation of the rectifier. The total capacity of two identical in capacity capacitors, connected in series, is equal to half the capacity of each of them.

When designing and repairing electronic equipment, there is often a need to check radio elements, including capacitors. We will talk about how to reliably check the serviceability of capacitors before using them.

The most accessible and widespread device with which you can check almost any capacitor, is a digital multimeter in ohmmeter mode.

The most important thing is to check capacitor for breakdown.

Breakdown capacitor- this is a malfunction associated with a change in the dielectric resistance between the plates capacitor due to exceeding the permissible operating voltage on the capacitor plates.

If the operating voltage is significantly exceeded capacitor, an electrical breakdown occurs between its plates. Pierced on the body capacitors You can detect darkening, swelling, dark spots and other external signs of element malfunction.

Since capacitor does not pass direct current, then the resistance between its terminals (plates) must be very large and limited only by the so-called leakage resistance. In real capacitors a dielectric, despite the fact that it is essentially an insulator, passes a small current. This current for a working capacitor is very small and is not taken into account. It is called leakage current.

This method is suitable for testing non-polar capacitors. In non-polar capacitors, in which the dielectric is mica, ceramics, paper, glass, air, the leakage resistance is infinitely large and if you measure the resistance between the terminals of such capacitor with a digital multimeter, the device will record an infinitely high resistance.

Usually, if you capacitor If there is an electrical breakdown, then the resistance between its plates is quite small - several units or tens of ohms. Punched capacitor, in fact, is an ordinary conductor.

In practice, check for breakdown of any non-polar capacitor you can do this:

Switch the digital multimeter to resistance measurement mode and set the largest possible resistance measurement limit.
Next, we connect the measuring probes to the terminals of the thing being tested. capacitor. If the capacitor is working properly, the device will not show any value and a 1 will light up on the display. This indicates that the leakage resistance capacitor more than 2 Megaohms. This is enough to judge the serviceability in most cases. capacitor. If the digital multimeter clearly detects any resistance less than 2 Megaohms, then most likely capacitor faulty

Please note that you cannot hold the leads and probes of the multimeter with both hands when taking measurements. Since in this case the device will record the resistance of your body, and not the leakage resistance capacitor. Since the resistance of the human body is less than the leakage resistance, the current will flow along the path of least resistance, that is, through your body along the hand-to-hand path. Therefore, do not forget about the rules when measuring resistance.

Checking polar electrolytics capacitors Using an ohmmeter is somewhat different from testing non-polar ones.

Leakage resistance polar capacitors is usually at least 100 kOhm. For better quality polar capacitors this value is at least 1 Megaohm. When checking such capacitors ohmmeter should first be discharged capacitor by short-circuiting the terminals.

Next, you need to set the resistance measurement limit to at least 100 kiloohms. For those mentioned above capacitors this will be the 200k (200,000 ohms) limit. Next, observing the polarity of connecting the probes, measure the leakage resistance capacitor. Since electrolytic capacitors have a fairly high capacity, then when checking capacitor will start charging. This process takes a few seconds, during which the resistance on the digital display will increase, and will continue to increase until capacitor will not charge. If the value of the measured resistance exceeds 100 kiloOhms, then in most cases one can judge with reasonable confidence that the capacitor.

Previously, when pointer ohmmeters were common among radio amateurs, checking capacitors was carried out in a similar way. In this case, the capacitor was charged from the ohmmeter battery and the resistance shown by the pointer instrument increased, ultimately reaching the leakage resistance value.

Based on the rate at which the needle of the measuring device deflects from zero to the final value, the capacity of the electrolytic capacitor. The longer the charging took (the longer the device arrow deviated), the correspondingly greater the capacity. capacitor. For capacitors with a small capacitance (1 - 100 µF), the needle of the measuring device deviated quite quickly, which indicated a small capacitance capacitor, but when checking capacitors with a large capacity (1000 microfarads or more), the needle deviated much more slowly.
Examination capacitors using an ohmmeter is an indirect method. A more accurate and truthful assessment of the health of the capacitor and its parameters can be obtained by obtaining a multimeter with the ability to measure the capacitance of the capacitor.

When checking electrolytic capacitors Before measuring the capacity, it is necessary to completely discharge the device being tested. capacitor. This rule should especially be followed when checking polar capacitors having large capacity and high operating voltage. If this is not done, the measuring device may be damaged.

For example, you often have to check the serviceability capacitors, which act as filters and are used in switching power supplies. Their capacity and operating voltage are quite high and, if not fully discharged, can lead to damage to the measuring device.

Therefore such capacitors Before checking, it should be discharged by short-circuiting the terminals (for low-voltage capacitors with low capacity), or by connecting a resistor with a resistance of 5-10 kiloOhms to the terminals (for high-voltage capacitors). When performing this operation, do not touch the terminals with your hands. capacitor, otherwise you can get an unpleasant electric shock when the plates are discharged. When shorting the terminals of a charged electrolytic capacitor a spark jumps. To prevent the occurrence of a spark, the high-voltage terminals capacitors and short-circuit through a resistor.

One of the significant malfunctions of electrolytic capacitors is a partial loss of capacity caused by increased leakage. In such cases, the capacity capacitor noticeably less than indicated on the case. It is quite difficult to determine such a malfunction using an ohmmeter. To accurately detect a fault such as loss of capacitance, you will need a capacitance meter, which is not available in every multimeter.

It is also difficult to detect such a malfunction using an ohmmeter. capacitor like a cliff. When broken capacitor electrically it consists of two insulated conductors without any capacitance.

For polar electrolytic capacitor An indirect sign of a break can be the absence of a change in the readings on the multimeter display when measuring resistance. For non-polar capacitors small capacity, it is almost impossible to detect a break, since a serviceable capacitor also has very high resistance.

Detect a break in capacitor is possible only with the help of instruments for measuring the capacitance of the capacitor.

In practice, a break in capacitors occurs quite rarely, mainly due to mechanical damage. Much more often when repairing equipment you have to replace capacitors, having electrical breakdown or partial loss of capacity.
For example, compact fluorescent lamps often fail due to electrical breakdown of capacitors in the electronic circuit of the converter.

The cause of the TV malfunction may be loss of capacity electrolytic capacitor in the power supply circuit.

The loss of capacity of electrolytic capacitors is easily detected by measuring the capacity of such capacitors using multimeters with a capacitance measurement function.
Malfunction capacitor can be determined by external inspection, for example, the housing of electrolytic capacitors has a notch gap in the upper part of the body. This indicates that an excessive voltage was applied to the capacitor, as a result of which the so-called “explosion” of the capacitor occurred. The housings of non-polar capacitors, when the operating voltage is significantly exceeded, tend to split, and splits and cracks form on the surface.

Such capacitor defects appear, for example, when an electronic device is exposed to a powerful electrical discharge during lightning discharges and strong voltage surges in the lighting network.

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, so 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.
In this picture:

1. Paper;
2. Foil;
3. Glass insulator;
4. Lid;
5. Frame;
6. Cardboard gasket;
7. Wrapping paper;
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 connecting 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 consists of two plates separated by a dielectric layer. If a constant voltage is applied to the plates, then one plate will be charged positively, the other negatively. After disconnecting the capacitor, the charges on the plates will remain, which allows this device to be used as an electrical energy storage device. The amount of accumulated energy (capacitance) depends on the area of ​​the plates, their material, properties and the type of dielectric laid between the plates. The basic unit of measurement for capacitance is farad (F). This is a fairly large value; in practice, fractions of a farad are usually used - microfarads (μF), nanofarads (nF), picofarads (pF).

1F = 1000000uF;
1uF = 1000nF;
1nF = 1000 pF.

The second parameter of any capacitor, which is very important, is the rated (operating) voltage of the capacitor. This is the voltage supplied to the plates, which cannot be exceeded, otherwise the capacitor will fail. The voltage in volts and capacitance are often indicated on the body of the capacitor itself.

The next parameter is not inherent to all types of capacitors - polarity. If the capacitor is polar, then only constant voltage can be applied to its terminals, with “+” of the source on the positive plate, “-” on the negative plate. Polarity is also indicated on the case, often by marking one terminal (either “+” or “-“).

This is how polarity is indicated on SMD capacitors

The “minus” strip is located opposite the “-” output

And on domestic capacitors the “plus sign” can be placed directly on the body (on the side or at the end)

This type always has a “minus” on the body

If the capacitor is non-polar, then it can operate in AC and DC circuits, and in the second case there is no need to monitor the voltage polarity.

In electrical diagrams, capacitors are designated as follows:

Here there is a non-polar capacitor on the left, and the second and third symbols correspond to a polar capacitor, and in the third picture the “+” sign may be absent.

And as an example:

Capacitors in the diagrams are designated by the symbol C, so capacitor C1 is non-polar with a capacity of 100 nanofarads, C2 is polar, with a capacity of 30 microfarads for a rated voltage of 15 V.

Important! You can replace the capacitor with any suitable capacitance and appropriate type, but at a voltage NOT LOWER than that indicated in the diagram. Higher please.

An electric capacitor is one of the most common radio elements; it serves to store electricity (charge). The simplest capacitor can be imagined as two metal plates (plates) and a dielectric that is located between them.

When a voltage source is connected to a capacitor, opposite charges appear on its plates (plates) and an electric field appears, attracting them to each other, and even after the power source is turned off, such a charge remains for some time and the energy is stored in the electric field between the plates.

In electronic circuits, the role of a capacitor can also consist not only in accumulating charge but also in separating the direct and alternating current components, filtering pulsating current and various other tasks.
Depending on the tasks and operating factors, capacitors are used in very different types and designs. Here we will look at the most popular types of capacitors.

Aluminum electrolytic capacitors

Ceramic single layer capacitors

Ceramic multilayer capacitors

For example K10-17A or K10-17B.
Unlike those described above, they already consist of several layers of metal plates and a dielectric in the form of ceramics, which allows them to have a higher capacity than single-layer ones and can be of the order of several microfarads, but the maximum voltage for this type is still limited to 50 volts.
They are mainly used as filter elements and can work properly with both direct and alternating and pulsating current.

Ceramic high voltage capacitors

Tantalum capacitors

A solid tantalum capacitor has four main parts: anode, dielectric, electrolyte (solid or liquid), and cathode.
In terms of operating properties, tantalum capacitors are similar to electrolytic capacitors, but the maximum operating voltage is limited to 100 volts, and the capacitance usually does not exceed 1000 μF.
But unlike electrolytic ones, this type has much lower self-inductance, which makes it possible to use them at high frequencies, up to several hundred kilohertz.

Polyester capacitors

Polypropylene capacitors

The advantage of these capacitors is not only the high voltage, but also the extremely low loss tangent, since tg? may not exceed 0.001, which allows the use of capacitors at high frequencies of several hundred kilohertz and their use in induction heaters and launchers of asynchronous electric motors.

Starting capacitors (CBB-60) can have a capacity of up to 1000 µF, which becomes possible due to the design features of this type of capacitor. A metallized polypropylene film is wound onto a plastic core, and the entire roll is covered with a compound on top.