Electrolytic capacitor

An electrolytic capacitor (abbr. electrolytic capacitor ) is a polarized capacitor, the anode electrode is made of a metal ( valve metal ) on which by electrolysis ( anode oxidation, forming) an insulating layer is produced, which forms the dielectric of the capacitor. The electrolyte (for example, an electrically conductive liquid or a conductive polymer ) is the cathode of the electrolytic capacitor.

Depending on the nature of the anode used in the electrolytic metal capacitors are divided into

• Aluminum electrolytic capacitors
• Tantalum electrolytic capacitors
• Niobium Electrolytic Capacitors

The main advantage of electrolytic capacitors is the - in relation to the volume of construction - relatively high capacity compared to the other two important families, the capacitor, that is the ceramic and the plastic film capacitors.

Electrolytic capacitors are polarized components, which may only be operated with DC voltage. A possible ripple voltage must not cause reversal. Exceptions are provided for the audio frequency range for crossover bipolar electrolytic capacitors. Reverse polarity, over voltage or ripple current overload destroy the dielectric and thus the capacitor. The destruction can have catastrophic consequences ( explosion, fire ) to itself.

• 7.1 General
• 7.2 Marking of polarity

Basic structure

Electrolytic capacitors, as almost all of the capacitors in the electronics, basically plate capacitors whose capacitance is greater, the larger the electrode area A and the dielectric constant is ε and the closer the electrodes are ( d) each other.

Here, the dielectric constant ε is composed of the electric field constant and the material-specific permittivity of the dielectric:

Base material of the electrolytic capacitors is the anode metal, which consists of fine-grain metal powder for aluminum electrolytic capacitors comprising an aluminum foil and tantalum and niobium electrolytic capacitors. The aluminum foil is electrochemically roughened, the tantalum and niobium powder is pressed and sintered. In both cases results in a roughened anode, the surface is significantly larger than that of a smooth surface. This increase in surface area is an important factor contributing to the relatively high capacitance of electrolytic capacitors over other capacitor families.

The anode surface is then " anodized " or "formed". In this case, an electrically insulating oxide layer is formed by applying a current source in the correct polarity in an electrolyte on the anode surface, the dielectric of the capacitor.

The dielectric strengths of these oxide layers are quite high. This work electrolytic capacitors with extremely thin dielectrics. Since it also can achieve any desired withstand voltage selectively to the formation, this thickness will vary the oxide layer even at the nominal voltage of the subsequent capacitor, so that at low voltages in modern electronics, the possibility of realizing thin films, is used. The extremely thin dielectric is the second important factor contributing to the relatively high capacitance of electrolytic capacitors over other capacitor families.

In electrolytic capacitors, there are three types, which are denoted respectively by the anode material used.

The following table gives an overview of the properties of different oxide materials. Electrolytic capacitors with titanium or zirconium as the anode are not so far been out of the development stage.

A suitable electrolyte, the pores of the roughened anode adapts perfectly as possible, forms the cathode of the electrolytic capacitor. It may consist of a liquid or gel electrolyte ( ion conductor ) or a solid electrolyte ( electron conductor ) composed. The power supply to the electrolyte film via the same metal as that of the anode or any other suitable contacting of the electrolyte. The capacitor cell thus constructed is then installed in a beaker and sealed (Al electrolytic capacitors ), or covered with a casing. The case of larger Al electrolytic capacitors had formerly often a valve in the form of a rubber stopper or, more recently, a cross-shaped Gehäusevorprägung to let excess pressure created by electrolyte evaporation under electrical overload escape targeted to.

History

The phenomenon that can form a layer on aluminum in an electrochemical process, which can pass an electrical current in only one direction, in the other direction, however, current blocking effect was discovered in 1875 by the French researchers Ducretet. This first " electric valve " metals with this property was the nickname of a valve metal. These include aluminum, tantalum, niobium, manganese, titanium, bismuth, antimony, zinc, cadmium, zirconium, tungsten, tin, iron, silver and silicon.

Since the one-sided barrier layer has a very high dielectric strength even at very thin layers, originated in 1896 with the idea that layer as the dielectric of a polarized capacitor with high capacitance exploit in a DC circuit. In 1897 the scientist Charles Pollack in Frankfurt was the patent DRP granted for the idea of ​​an "electrical fluid capacitor with aluminum electrodes " 92564, which became the basis of all subsequent electrolytic capacitors.

In the picture the corrugated anode of an aluminum electrolytic capacitor can be seen, which was called at the time " fluid condenser ". The corrugated anode was installed free floating in a metal cup, which served as the cathode terminal simultaneously. This beaker was then a "wet" electrolyte filled, while also marking for a water- based electrolyte was " wet". The advantage of these capacitors was that they were based on the realized value of capacitance significantly smaller and cheaper than all other technical capacitors of the time.

The first commercial aluminum electrolytic capacitors have been used in 1892 as a motor -start capacitors for starting of single-phase AC motors. Beginning of the 20th century were the anti-jamming of telephone systems in Germany " electrolytic capacitors " used to suppress the ripple noise of the power generator on the lines. These capacitors were all provided with aqueous electrolyte and used the cup as the cathode. They had quite high residual current values ​​for chlorine-containing impurities and had a limited service life.

Only with the invention of the "dry" aluminum electrolytic capacitor by Samuel Ruben in 1925 started the actual development of the electrolytic capacitors. S. Ruben wanted the usual water-containing electrolytes because of the aggressiveness of the water compared to aluminum (see Capacitor Plague ) by a water-free, in the parlance "dry", replace electrolytes, which was less aggressive. But because this electrolyte had a poorer conductivity, was the long way of the ions in the electrolyte from the anode to the cup wall, the internal resistance too high. Ruben therefore introduced a second aluminum foil as a current supply to the electrolyte with a thin electrolyte - impregnated separator ( paper) was protected from direct contact with the anode foil. This was the way that the ions had to travel in the electrolyte, considerably smaller, the internal resistance ( ESR) significantly lower. Both aluminum foils with the paper strip as a separator could be layered or wrapped and impregnated with the still liquid electrolyte, with the further advantage that the capacity per unit volume was much larger. ( "Anhydrous" within the meaning of ) this "dry" and wound aluminum electrolytic capacitor began in 1931 at Cornell Dubilier in South Plainfield, NJ, United States the first industrial -scale production of electrolytic capacitors. With the invention of S. Ruben, the aluminum electrolytic capacitors could be made ​​small and inexpensive enough so that so that the then new radios were affordable. At the next stormy development of this technique electrolytic capacitors had a not insignificant share.

The first tantalum electrolytic capacitors and tantalum foil glycol or lithium chloride as an electrolyte was prepared from the 1930 Fansteel Metallurgical Corporation for military purposes. The significant development of tantalum electrolytic capacitors was only after the Second World War. In early 1950, succeeded General Electric to produce newly developed tantalum electrolytic capacitors with sintered body and sulfuric acid as the electrolyte. 1952 led a targeted search for a solid electrolyte by Taylor, Haring, McLean and Power to the invention of tantalum sintered capacitor to the semiconducting manganese dioxide as a solid electrolyte. Within a few years, in 1955 at Bell Laboratories by RL Robinson and 1956 at Sprague Electric Company, this technology has been developed in the U.S. and so perfected that very soon a number of manufacturers in Japan and Europe, large-scale production started. The development was particularly favored by the design of the tantalum capacitor drops (Ta - pearls ) that have been specifically used quickly in large series in radio and television sets. The offered small nominal voltages up to 50 V ranged in many areas of circuit completely.

Parallel to the development of tantalum electrolytic capacitors in the west end of the 1960s were developed in the former Soviet Union, due to the availability of the base metal, electrolytic capacitors with niobium as the anode material. They took there the place, in the West, had the military tantalum electrolytic capacitors with sintered anode and manganese dioxide electrolyte. With the collapse of the Iron Curtain, this know -how has been publicized in the West. Since niobium is much more abundant than tantalum as a raw material and is also cheaper, the 1990s were included in the program of some big manufacturers in the Far East niobium electrolytic capacitors from the end.

Main objective in the development of all electrolytic capacitors in the past few decades in addition to the reduction of size to reduce the internal ohmic losses (ESR) and the reduction of internal inductance ( ESL). With the development of new solid electrolyte systems based on organic compounds such as TCNQ ( tetracyanoquinodimethane ) from the mid- 1970s and conductive polymers ( polypyrrole ) in the 1980s made ​​it the developers of electrolytic capacitors, the user demands for ever-smaller internal losses with the Elko technology to follow. The reduction of internal inductance could be achieved with the multi -anode technique in which several anode blocks are connected in parallel in a capacitor housing. In this variant both ESR and ESL are connected in parallel and the parameters corresponding to the number of parallel blocks reduced. Today surface mountable aluminum tantalum and niobium electrolytic capacitors polymer ESR values ​​reach less than 10 milliohms. Thus, they are competitive even against multi-layer ceramic capacitors ( MLCC).

Designs

Aluminum electrolytic capacitors form the bulk of the electrolytic capacitors used in electronics because of the large size and diversity of its inexpensive production; Tantalum electrolytic capacitors found in military technology and in devices with small space use; Niobium electrolytic capacitors in the mass market a new development, are in competition with tantalum electrolytic capacitors.

Electrolyte

Its name is the electrolytic capacitor by the electrolyte, the conductive fluid forming the actual cathode of the capacitor. Since the roughened structures of the anode surface continue into the structure of the oxide layer, the dielectric, has the counter electrode, the cathode, adjust as precisely as possible to it. With a liquid that is easy to reach.

The main electrical property of an electrolyte in the electrolytic capacitor is its electrical conductivity, which physically is an ion - conductivity in liquids. A liquid electrolyte always consists of a mixture of solvents and additives to meet given requirements.

On the operating electrolyte diverse demands are made, including high conductivity, oxygen supplier for Formierprozesse and self-healing, the largest possible temperature range, chemical stability, high flash point, chemical compatibility with the materials used in the condenser, low viscosity, environmental friendliness and low costs.

The diversity of these requirements has a variety of proprietary solutions result. For aluminum electrolytic capacitors can be roughly summarized form three groups:

• Aqueous electrolytes are weak acids with additions of ethylene glycol ( water-glycol - electrolytes ), suitable for applications up to 105 ° C for so-called low - ESR electrolytic capacitors
• Anhydrous solvents based electrolytes, for example N, N- dimethylformamide or N, N-dimethylacetamide, suitable for applications up to about 105 ° C, and good long-term behavior
• Anhydrous solvents electrolytes, on the basis of γ -butyrolactone - based, suitable for applications up to about 125 ° C. The latter lead to electrolyte capacitors with very good long-term behavior.

As a liquid electrolyte for electrolytic capacitors, tantalum usually sulfuric acid is used.

In addition to liquid and paste-like electrolyte systems electrolytic capacitors can also be prepared with solid electrolyte systems. Such solid electrolytes of the semiconductor of manganese ( manganese dioxide, MnO 2 ), of a conductive salt ( TCNQ) or polymer (e.g., polypyrrole ) exist.

The combination of anode materials for electrolytic capacitors and possible electrolytes, a whole series of Elkotypen have formed each having its specific advantages and disadvantages of its own. A rough outline of the main characteristics of the different types are in the following table.

The so-called "wet" Al electrolytic capacitors were and are the cheapest devices in the field of high capacitance values ​​and the range of higher voltages. They not only provide the cost-effective solutions for screening and buffering, but are also relatively insensitive to transients and surges. Provided that in a circuit configuration space is restricted or voltages greater than 50 V is required, are aluminum electrolytic capacitors with non-solid electrolyte, with the exception of military applications to find throughout the electronics.

Tantalum electrolytic capacitors have in the form of surface-mount "Ta - chips" in all areas of industrial electronics firmly established as reliable components for devices where space is limited or you want to work in a large temperature range as possible without large parameter deviations. In the field of military and space applications only tantalum electrolytic capacitors have ever approvals.

Niobium electrolytic capacitors are in direct competition with industrial tantalum electrolytic capacitors, their properties are comparable. Because of their slightly lower weight, they offer an advantage over the tantalum electrolytic capacitors for applications with high demands on vibration and shock resistance. In addition, niobium is more readily available.

Switching characters

The circuit symbol of the polarized electrolytic capacitor, the positive pole (anode ) is characterized by a hollow square, the negative terminal through a completed. For a bipolar electrolytic capacitor anode, the capacitor having two films is established. Therefore, the circuit symbol of two hollow rectangles is formed.

Unique features compared to other capacitor types

The following features of electrolytic capacitors are described that distinguish these capacitors from other capacitor types.

Equivalent circuit

The general electrical characteristics of capacitors in technical applications in the international field harmonized by the Sectional specification IEC 60384-1, the EN is published in Germany as DIN 60384-1 in February 2002. They are described by an idealized series equivalent circuit.

This includes:

• , The capacitance of the capacitor,
• , The parallel resistance to the ideal capacitor, the leakage current (leakage current ) of the electrolytic capacitor represents,
• , The equivalent series resistance, he summarizes the ohmic losses of the device. This effective resistance is generally called only " ESR" ( equivalent series resistance )
• , The equivalent series inductance, it summarizes the inductance of the device together, it is commonly called just " ESL " ( Equivalent Series Inductivity L).

Capacity

The capacitance of an electrolytic capacitor is frequency dependent. At the frequency "0", with DC voltage, an electrolytic capacitor has a charge capacity, the capacity is called DC voltage. It is measured with a time measurement of the charge or discharge curve of an RC member. The DC voltage capacity is about 10 to 15% higher than the capacitance that is measured by the frequency prescribed by the standard of 100/ 120 Hz. Herein, electrolytic capacitors differ from other types capacitor, whose capacitance is measured at 1 kHz.

Capacitance tolerance

The capacity tolerance of electrolytic capacitors, formerly -10 / 50 % or -10 / 30 %, nowadays usually ± 20%, as compared to other capacitor families, quite large. Since electrolytic capacitors are not used in the frequency-determining circuits, where close tolerances are required capacity, this tolerance range, which comes mainly from the scattering of Aufraugrades the anode is sufficient, usually the requirements.

Dielectric strength

The thickness of the dielectric of the electrolytic capacitor determines its dielectric strength. Since it is made specifically for the rated voltage of the capacitor, exceeding the specified voltage limits leads to the destruction of the capacitor, that is, neither the rated voltage, the peak voltage or the polarity reversal or Falschpolspannung may be exceeded or undershot.

Reverse voltage

The characteristic of valve metals, to form an electrically locking in this direction the oxide layer on the anode surface when a voltage in the correct polarity. In Gegenpolrichtung this oxide layer has semiconducting properties. The polarity of which is applied to the valve metal, is reversed so, when the voltage goes beyond a threshold, a current can flow. In addition, the oxide layer forms back. The result is that it may lead to breakdowns due to the oxide. A longer time on the adjacent electrolytic capacitor polarity reversal or Falschpolspannung thus leads inevitably to a short circuit and thus the destruction of the capacitor. The amount of the maximum permissible Falschpolspannung depends on the design of the respective electrolytic capacitor. Tantalum electrolytic capacitors with solid electrolyte behave differently than aluminum electrolytic capacitors with liquid electrolytes.

Current carrying capacity

A DC voltage of the superimposed alternating current ( ripple current ) causes the charging and discharging in the electrolytic capacitor. This alternating current flows through the ESR results in frequency dependent losses which heat up the capacitor. This heat is dissipated to the environment. How quickly this happens depends on the dimensions of the capacitor and other conditions, such as forced cooling off. The specified ripple current must not be exceeded within the rated temperature range. Exceeding this limit will damage the capacitor.

Impedance Z and effective resistance ESR

Analogous to Ohm's law, where the ratio of DC voltage UDC and DC current IDC is equal to a resistance R, the ratio of AC voltage and AC current IAC UAC is:

AC resistance or impedance called. It is the magnitude of the complex impedance of the capacitor at the selected measurement frequency. ( In the data sheets of capacitors only the impedance, ie the magnitude of the impedance is specified ).

Are the equivalent series values ​​of a capacitor is known, the impedance can also be calculated on these values. It is then the sum of the geometric (complex) the addition of the active and the reactive impedances, that is, the equivalent series resistance ESR, and the inductive reactance XL of the capacitive reactance XC less. The two reactances have with angular frequency ω on the following relationships:

Which is obtained for the impedance of the following equation:

( for the derivation of the sign convention used see impedance).

In the special case of resonance, in which the capacitive and the inductive reactance is equal to (XC = XL ), the impedance is equal to that of the capacitor to the value at which all the ohmic losses of the capacitor are combined.

In some, especially older data sheets of tantalum and aluminum electrolytic capacitors, the loss factor is specified instead of the. It works with the following formula in the be converted:

It should be noted that the conversion of the frequency is considered due to the strong dependence of the capacitance of which only the frequency at which the loss factor was measured.

Impedance behavior

Feature of the aluminum electrolytic capacitors with liquid electrolyte, the relatively high capacitance values ​​that can be achieved with this technology. Since these capacitors are mainly used in power electronic circuits and they often feature the power frequency of 50/60 Hz in the electrical behavior of the supply voltage flows with, must be " screened " low frequencies. The impedance behavior of electrolytic capacitors with high capacity accommodates such use.

Are shown in the picture typical curves of the impedance as a function of frequency for various capacitor types and capacitors with different capacities. The larger the capacity is, the lower the frequency, the filter can be of the capacitor (seven). The residual resistance at the inflection point of each curve shape is equated with the ESR of that capacitor. Aluminum electrolytic capacitors with polymer electrolytes (shown with "polymer" labeled ) have significantly lower ESR values ​​than Al electrolytic capacitors with liquid electrolytes (labeled in the picture with " Al- Elko ").

Residual current

A special feature of electrolytic capacitors is the so-called residual current (English leakage current ), formerly also known as leakage current. The leakage current of an electrolytic capacitor of the direct current which flows through it when a DC voltage is applied to the correct polarity. The rest includes all current caused by chemical processes and mechanical damage of the dielectric and by tunneling effects undesirable DC currents that can pass the dielectric. The residual current is voltage-, time-and temperature-dependent and depends on the previous history of the capacitor, for example, by soldering and of the chemical compatibility between the electrolyte and the oxide layer. For aluminum electrolytic capacitors with liquid electrolytes he is also dependent on the previous storage period. The leakage current is specified mostly by multiplying the nominal capacitance value and the nominal voltage at which a small fixed value is not added, for example:

This value is measured with the rated voltage, is measured after a prescribed time, for example, 2 minutes or 5 minutes observed. Aluminum and tantalum electrolytic capacitors have different residual current behavior. Aluminum electrolytic capacitors with liquid electrolytes with relatively little security in the thickness of the oxide layer, the dielectric prepared. In addition, aluminum and its oxide is relatively sensitive to aggressive or water containing electrolytes. Therefore, the so-called "wet electrolytics " compared the Elko technologies when you turn the highest residual current.

Tantalum electrolytic capacitors with solid electrolyte, but also aluminum electrolytic capacitors with solid electrolyte ( Braunstein, TCNQ, polymer ) can be built with much greater certainty as to the thickness of the oxide layer. This usually causes a greater dielectric strength of the dielectric and during power thus a smaller residual current.

Even better properties in terms of the residual stream have tantalum electrolytic capacitors with liquid electrolytes. Since the introduction of solid electrolyte may be present minor damage to the oxide layer, which is not the case with liquid electrolyte, these capacitors are compared in the best residual current switching behavior.

The residual current in all electrolytic capacitors, caused less and less the longer lie through self- healing effects, the capacitors to voltage.

Life

Generally

The service life of components, including electrolytic capacitors, results from the reliability of the device and is calculated according to the failures that occur during operation. When failure is called here an error occur in operation or in an exam, either the inoperability of the capacitor leads (full failure: Short circuit or interruption) or manifests itself through an excess of electrical parameters ( change in failure).

If a certain percentage of failures is exceeded in a batch ( full outages and failures change are considered equivalent), one speaks of the " end of life " or "end of service life " of this lot. After older, today retracted DIN standards exceeding 1% of failures in a batch was synonymous with their end of service life for industrial equipment.

The different structure of the various Elko families with either solid or liquid electrolyte determines a completely different definition of life is acknowledged.

Lifetime (reliability) in electrolytic capacitors with solid electrolyte

In electrolytic capacitor families with solid electrolyte, which can not evaporate, the number of so-called " random failures " determined randomly and infrequently occurring Full failures during the operating period, an indication of life, which then usually as a failure rate λ is given. Change losses play only a minor role here. The failure rate is given for a specific temperature in FIT ( Failure In Time ) with the unit failures per hour. This value is determined by the producers from the experience of his life tests. The failure rate of the manufacturer, which applies only to a certain temperature, with the aid of multipliers, which are usually taken from the Handbook MIL -HDBK- 217F Reliability Prediction of Electronic Equipment, be converted for other operating conditions.

Their lifespan is then obtained from the defined by the device manufacturer failure percentage of the calculated failure rate.

Life in electrolytic capacitors with non-solid electrolyte

Electrolytic capacitors with liquid electrolytes take in the specification of life a special position. The liquid electrolyte evaporates over the operating time and determined by its evaporation rate, the working life of the electrolytic capacitors. There occurs a loss of electrolyte, and that the faster the higher the temperature of the capacitor, which results from the ambient temperature and the self-heating due to current load. With decreasing amount of electrolyte but also change the electrical parameters of the capacitor, the capacitance decreases and the equivalent series resistance ESR and impedance increase. The result is that the lifetime of the aluminum electrolytic capacitors with liquid electrolyte is determined essentially by crossing of characteristic values ​​, that is by change failures. The random failures ( blackouts ) during the lifetime are usually negligible.

The service life of electrolytic capacitors with non-solid electrolyte is specified in a notation that result from the combination of the maximum test time in hours in the life test ( endurance test) and the test temperature, which is the maximum permissible ambient temperature, results, eg 2000 h / 85 h/105 ° C or 2000 ° C.

The evaporation of the electrolyte and the associated diffusion of gases out of the electrolytic capacitor is a function of temperature. However, an operation of the capacitors at a temperature lower than the maximum permissible temperature results in a lower rate of diffusion of the electrolyte, so a long service life. The associated increase in longevity mostly by the so-called 10-K - rule ( Arrhenius rule RGT rule) described the world in the data sheets of many manufacturers, which results in a doubling of life span per 10 K temperature reduction.

With

• Lx = to be calculated lifetime
• LSpec = Specified service life ( useful life, load life, service life)
• T0 = upper limit temperature ( in ° C or K)
• TA = condenser temperature ( in ° C or K)

Using this formula, which results in a doubling of life for every 10 ° C temperature reduction, can be the life of the capacitor at a given operating temperature roughly estimated.

Example: From a manufacturer's specification of 2000 h/105 ° C and an intended operating temperature of the capacitor by 65 ° C results in the following statement:

A 4 -time doubling () the specified life of 2000 h The expected life of the capacitor is thus calculated to be 2.000 × 16 h = 32,000 h, which is about 3.7 years. A capacitor with specification 2000 h/85 ° C is reached at the same operating temperature only a calculated service life of 8,000 hours, which is only about one year.

Storage capacity and pulse - current capability

Electrolytic capacitors, in particular aluminum electrolytic capacitors, own, compared with plastic film and ceramic capacitors, a very high capacitance per unit volume. In other words, the energy density is quite high. However, compared to the relatively new double-layer capacitors (DLC), the energy density of the aluminum electrolytic capacitors is significantly lower. Since the current-carrying capacity, both in single as well as in off operations in the capacitors is significantly higher than for DLC capacitors results in the area of ​​application establishes a clear separation of the two capacitor families. Aluminum electrolytic capacitors to buffer rapid energy peaks and smooth DC voltages by screening of alternating currents to ground, DLC and capacitors, as shown in the picture on the right, accumulators buffer DC voltages and provide energy for longer periods.

Dielectric Absorption

The dielectric absorption is an undesired charge storage of the dielectric. If a capacitor is discharged shortly, builds up on the electrodes after a few seconds to minutes, again a part of the previously applied voltage. The dielectric had a portion of the charge absorbed and gives him now gradually released. This recharging effect is known as dielectric absorption or dielectric relaxation. The magnitude of the absorption is expressed in relation to the initially applied voltage, and depends on the dielectric used. Electrolytic capacitors with a dielectric absorption of about 10 to 15% of a relatively high value compared with other capacitor technology. This can sometimes be relatively high voltages ( even a few volts ) lead, which can pose a risk: It can be caused by damage to semiconductors or sparking when shorting of terminals. But in measuring circuits of this effect is rather undesirable because it leads to incorrect measurements. Larger aluminum electrolytic capacitors are therefore typically transported or shipped with a shorting jumper across the terminals.

Identification

Generally

The marking of electrolytic capacitors knows no color coding. The color coding used earlier of the tantalum bead capacitors no longer exists today. If you have enough space to the capacitors should be characterized by appropriate imprints with:

Capacity, tolerance, and date of manufacture can be labeled with short identifier 60062 EN. Examples of a short marking of the rated capacity ( microfarads ):

The date of manufacture is often printed in accordance with international standards in abbreviated form.

Marking of polarity

• Marking of polarity

In electrolytic capacitors with non-solid electrolyte, the negative pole is marked.

To identify the polarity, there are several variants:

• In the axial / design of the negative terminal is located connected to the housing, the positive pole is insulated. On the positive side there is a circumferential groove. In older electrolytic capacitors, the negative side is marked with an additional color ring.
• In the stationary design ( radial design or " single ended " called ) runs on the negative side, a vertical minus mark. In addition, not taped goods, the plus terminal for bulk, longer than the negative terminal.
• For SMD capacitors located on the visible part of the cup a negative marker, usually a black bar.

In electrolytic capacitors with solid electrolyte, the positive pole is marked.

• When tantalum capacitors in bead form the positive pole is marked with a plus.
• In the axial / design of the negative terminal is located connected to the housing, the positive pole is insulated. On the positive side there is a circumferential groove.
• In SMD electrolytic capacitors, the positive pole is marked with a bar.

Applications

Typical applications for electrolytic capacitors are:

• Smoothing and buffer capacitor for smoothing or screening of rectified AC voltages.
• Seven of AC voltage components within a circuit (derivation of alternating currents ), for example, in DC / DC converters
• Buffers of DC power supplies with load changes
• Buffer for PFC circuits (Power Factor Control = power factor improvement) in frequency converters and uninterruptible power supplies (UPS)
• Addition and removal of AC signals, for example, in low frequency amplifiers, when a potential difference exists (level shifting ). It should be noted that the electrolytic capacitors require a corresponding bias
• Energy storage, such as in electronic flash devices
• Charge collector in timers, such as turn signals
• Bipolar ( non-polarized ) electrolytic capacitors as a trade or motor starting capacitors ( start capacitor ) for asynchronous motors
• Tonfrequenzkondensatoren in crossovers of speakers
• Smoothing the PWM for LED drivers