What is the most common use for capacitors?
Capacitor
The physical form and construction of practical capacitors vary widely and many capacitor types are in common use. Most capacitors contain at least two electrical conductors often in the form of metallic plates or surfaces separated by a dielectric medium. A conductor may be a foil, thin film, sintered bead of metal, or an electrolyte. The nonconducting dielectric acts to increase the capacitor's charge capacity. Materials commonly used as dielectrics include glass, ceramic, plastic film, paper, mica, and oxide layers. Capacitors are widely used as parts of electrical circuits in many common electrical devices. Unlike a resistor, an ideal capacitor does not dissipate energy.
Film capacitor
The most popular simple snubber circuit consists out of a film capacitor and a resistor in series, connected in parallel with a semiconductor component to suppress or damp undesirable voltage spikes. The capacitor absorbs the inductive turn-off peak current temporarily, so that the resulting voltage spike is limited. But the trend in modern semiconductor technology is towards higher power applications, which increases the peak currents and switching speeds. In this case, the boundary between a standard electronic film capacitor and a power capacitor is blurred, so that larger snubber capacitors belong more in the area of power systems, electrical installations and plants.
Capacitor
Polymer capacitors (OS-CON, OC-CON, KO, AO) use solid conductive polymer (or polymerized organic semiconductor) as electrolyte and offer longer life and lower ESR at higher cost than standard electrolytic capacitors.
Advanced Linear Devices
Supercapacitors are an emerging technology used for energy storage in growing numbers of electronic circuit board applications. However, it is often necessary to combine individual supercapacitors a series to store and discharge a level of useful amounts such as five volts.
Capacitor
Mechanically controlled variable capacitors allow the plate spacing to be adjusted, for example by rotating or sliding a set of movable plates into alignment with a set of stationary plates. Low cost variable capacitors squeeze together alternating layers of aluminum and plastic with a screw. Electrical control of capacitance is achievable with varactors (or varicaps), which are reverse-biased semiconductor diodes whose depletion region width varies with applied voltage. They are used in phase-locked loops, amongst other applications.
Film capacitor
For simple higher-frequency filter circuits, or in voltage regulator or voltage doubler circuits, low-cost metallized polyester film capacitors provide long-term stability, and can replace more-expensive tantalum capacitors. Because capacitors pass AC signals but block DC, film capacitors with their high insulation resistance and low self-inductance are well-suited as signal coupling capacitors for higher frequencies. For similar reasons, film capacitors are widely used as decoupling capacitors to suppress noise or transients.
Applications of capacitors
Because capacitors pass AC but block DC signals (when charged up to the applied DC voltage), they are often used to separate the AC and DC components of a signal. This method is known as "AC coupling" or "capacitive coupling". Here, a large value of capacitance, whose value need not be accurately controlled, but whose reactance is small at the signal frequency, is employed.
Applications of capacitors
Reservoir capacitors are used in power supplies where they smooth the output of a full or half wave rectifier. They can also be used in charge pump circuits as the energy storage element in the generation of higher voltages than the input voltage.
SAL electrolytic capacitor
SAL electrolytic capacitors are used for filtering, smoothing coupling and decoupling applications in industrial, medical and automotive equipment. 
The axial style of SAL capacitors has military and high professional applications up to 200 °C.
Capacitor types
Supercapacitors are divided into three families, based on the design of the electrodes:Supercapacitors bridge the gap between conventional capacitors and rechargeable batteries. They have the highest available capacitance values per unit volume and the greatest energy density of all capacitors. They support up to 12,000 farads/1.2 volt, with capacitance values up to 10,000 times that of electrolytic capacitors. While existing supercapacitors have energy densities that are approximately 10% of a conventional battery, their power density is generally 10 to 100 times greater. Power density is defined as the product of energy density, multiplied by the speed at which the energy is delivered to the load. The greater power density results in much shorter charge/discharge cycles than a battery is capable, and a greater tolerance for numerous charge/discharge cycles. This makes them well-suited for parallel connection with batteries, and may improve battery performance in terms of power density.
Filter capacitor
Electrolytic capacitors are usually used due to high capacity at low cost and low size. Smaller non-electrolytics may be paralleled with these to compensate for electrolytics' poor performance at high frequencies.
Capacitor types
AC loads can occur in AC motor run capacitors, for voltage doubling, in snubbers, lighting ballast and for power factor correction PFC for phase shifting to improve transmission network stability and efficiency, which is one of the most important applications for large power capacitors. These mostly large PP film or metallized paper capacitors are limited by the rated reactive power VAr.
DC-to-DC converter
Switched capacitor converters rely on alternately connecting capacitors to the input and output in differing topologies. For example, a switched-capacitor reducing converter might charge two capacitors in series and then discharge them in parallel. This would produce the same output power (less that lost to efficiency of under 100%) at, ideally, half the input voltage and twice the current. Because they operate on discrete quantities of charge, these are also sometimes referred to as charge pump converters. They are typically used in applications requiring relatively small currents, as at higher currents the increased efficiency and smaller size of switch-mode converters makes them a better choice. They are also used at extremely high voltages, as magnetics would break down at such voltages.
Variable capacitor
The most common form arranges a group of semicircular metal plates on a rotary axis ("rotor") that are positioned in the gaps between a set of stationary plates ("stator") so that the area of overlap can be changed by rotating the axis. Air or plastic foils can be used as dielectric material.
By choosing the shape of the rotary plates, various functions of capacitance vs. angle can be created, e.g. to obtain a linear frequency scale. Various forms of reduction gear mechanisms are often used to achieve finer tuning control, i.e. to spread the variation of capacity over a larger angle, often several turns.
Applications of capacitors
Capacitors may retain a charge long after power is removed from a circuit; this charge can cause dangerous or even potentially fatal shocks or damage connected equipment. For example, even a seemingly innocuous device such as a disposable camera flash unit powered by a 1.5 volt AA battery contains a capacitor which may be charged to over 300 volts. This is easily capable of delivering a shock. Service procedures for electronic devices usually include instructions to discharge large or high-voltage capacitors. Capacitors may also have built-in discharge resistors to dissipate stored energy to a safe level within a few seconds after power is removed. High-voltage capacitors are stored with the terminals shorted, as protection from potentially dangerous voltages due to dielectric absorption.
Capacitor
Electrolytic capacitors and supercapacitors are used to store small and larger amounts of energy, respectively, ceramic capacitors are often used in resonators, and parasitic capacitance occurs in circuits wherever the simple conductor-insulator-conductor structure is formed unintentionally by the configuration of the circuit layout.
Applications of capacitors
Capacitive touch switches are now used on many consumer electronic products.
Capacitor
Porcelain was used in the first ceramic capacitors. In the early years of Marconi's wireless transmitting apparatus porcelain capacitors were used for high voltage and high frequency application in the transmitters. On the receiver side smaller mica capacitors were used for resonant circuits. Mica dielectric capacitors were invented in 1909 by William Dubilier. Prior to World War II, mica was the most common dielectric for capacitors in the United States.
Capacitor
In car audio systems, large capacitors store energy for the amplifier to use on demand. Also, for a flash tube, a capacitor is used to hold the high voltage.
Electrolytic capacitor
Tantalum electrolytic capacitors with solid electrolyte as surface-mountable chip capacitors are mainly used in electronic devices in which little space is available or a low profile is required. They operate reliably over a wide temperature range without large parameter deviations. In military and space applications only tantalum electrolytic capacitors have the necessary approvals.
Applications of capacitors
Some old, large oil-filled capacitors contain polychlorinated biphenyls (PCBs). It is known that waste PCBs can leak into groundwater under landfills. Capacitors containing PCB were labelled as containing "Askarel" and several other trade names. PCB-filled capacitors are found in very old (pre 1975) fluorescent lamp ballasts, and other applications.
Energy harvesting
In general, energy can be stored in a capacitor, super capacitor, or battery. Capacitors are used when the application needs to provide huge energy spikes. Batteries leak less energy and are therefore used when the device needs to provide a steady flow of energy. Compared to batteries, super capacitors have virtually unlimited charge-discharge cycles and can therefore operate forever enabling a maintenance-free operation in IoT and wireless sensor devices
Capacitor
For air dielectric capacitors the breakdown field strength is of the order 2–5 MV/m (or kV/mm); for mica the breakdown is 100–300 MV/m; for oil, 15–25 MV/m; it can be much less when other materials are used for the dielectric. The dielectric is used in very thin layers and so absolute breakdown voltage of capacitors is limited. Typical ratings for capacitors used for general electronics applications range from a few volts to 1 kV. As the voltage increases, the dielectric must be thicker, making high-voltage capacitors larger per capacitance than those rated for lower voltages.
Applications of capacitors
In car audio systems, large capacitors store energy for the amplifier to use on demand.
Capacitor types
Some film capacitors of special shapes and styles are used as capacitors for special applications, including RFI/EMI suppression capacitors for connection to the supply mains, also known as safety capacitors, Snubber capacitors for very high surge currents, Motor run capacitors, AC capacitors for motor-run applications
Filter capacitor
Ceramic disc capacitors are usually used in snubber circuits for low voltage motors for their low inductance and low cost.
Aluminum electrolytic capacitor
Due to their relatively high capacitance values aluminum electrolytic capacitors have low impedance values even at lower frequencies like mains frequency. They are typically used in power supplies, switched-mode power supplies and DC-DC converters for smoothing and buffering rectified DC voltages in many electronic devices as well as in industrial power supplies and frequency converters as DC link capacitors for drives, inverters for photovoltaic, and converters in wind power plants. Special types are used for energy storage, for example in photoflash or strobe applications or for frequency coupling in audio applications.
Polymer capacitor
The predominant application of all electrolytic capacitors is in power supplies. They are used in input and output smoothing capacitors, as decoupling capacitors to circulate the harmonic current in a short loop, as bypass capacitors to shunt AC noise to the ground by bypassing the power supply lines, as backup capacitors to mitigate the drop in line voltage during sudden power demand or as filter capacitor in low-pass filter to reduce switching noises. In these applications, in addition to the size, are the capacitance, the impedance "Z", the ESR, and the inductance ESL important electrical characteristics for the functionality of these capacitors in the circuits.
Microwave cavity
Conventional capacitors use air, mica, ceramic or perhaps teflon for a dielectric. Even with a low loss dielectric, capacitors are also subject to skin effect losses in their leads and plates. Both effects increase their equivalent series resistance and reduce their Q.
Capacitor types
Some ceramic capacitors of special shapes and styles are used as capacitors for special applications, including RFI/EMI suppression capacitors for connection to supply mains, also known as safety capacitors, X2Y® and three-terminal capacitors for bypassing and decoupling applications, feed-through capacitors for noise suppression by low-pass filters and ceramic power capacitors for transmitters and HF applications.
Tantalum capacitor
Tantalum electrolytic capacitors, as well as other conventional capacitors, have two electrical functions. For timers or similar applications, capacitors are seen as a storage component to store electrical energy. But for smoothing, bypassing, or decoupling applications like in power supplies, the capacitors work additionally as AC resistors to filter undesired AC components from voltage rails. For this (biased) AC function the frequency dependent AC resistance (impedance ""Z"") is as important as the capacitance value.
Film capacitor
Polypropylene film capacitors are widely used for EMI suppression, including direct connection to the power supply mains. In this latter application, they must meet special testing and certification requirements concerning safety and non-flammability.
Capacitor
Capacitors are widely used in electronic circuits for blocking direct current while allowing alternating current to pass. In analog filter networks, they smooth the output of power supplies. In resonant circuits they tune radios to particular frequencies. In electric power transmission systems, they stabilize voltage and power flow. The property of energy storage in capacitors was exploited as dynamic memory in early digital computers.
Capacitor
Several other types of capacitor are available for specialist applications. Supercapacitors store large amounts of energy. Supercapacitors made from carbon aerogel, carbon nanotubes, or highly porous electrode materials, offer extremely high capacitance (up to 5 kF ) and can be used in some applications instead of rechargeable batteries. Alternating current capacitors are specifically designed to work on line (mains) voltage AC power circuits. They are commonly used in electric motor circuits and are often designed to handle large currents, so they tend to be physically large. They are usually ruggedly packaged, often in metal cases that can be easily grounded/earthed. They also are designed with direct current breakdown voltages of at least five times the maximum AC voltage.
Capacitor types
They find use as converters to change voltage, current or frequency, to store or deliver abruptly electric energy or to improve the power factor. The rated voltage range of these capacitors is from approximately 120 V AC (capacitive lighting ballasts) to 100 kV.
Electronic component
Capacitors store and release electrical charge. They are used for filtering power supply lines, tuning resonant circuits, and for blocking DC voltages while passing AC signals, among numerous other uses.
Capacitor
Glass and mica capacitors are extremely reliable, stable and tolerant to high temperatures and voltages, but are too expensive for most mainstream applications.
Film capacitor
Unique mechanical properties of plastic and paper films in some special configurations allow them to be used in capacitors of very large dimensions. The larger film capacitors are used as power capacitors in electrical power installations and plants, capable of withstanding very high power or very high applied voltages. The dielectric strength of these capacitors can reach into the four-digit voltage range.
Applications of capacitors
In schematic diagrams, a capacitor used primarily for DC charge storage is often drawn vertically in circuit diagrams with the lower, more negative, plate drawn as an arc. The straight plate indicates the positive terminal of the device, if it is polarized (see electrolytic capacitor).
Ceramic capacitor
Ceramic capacitors, especially multilayer ceramic capacitors (MLCCs), are the most produced and used capacitors in electronic equipment that incorporate approximately one trillion (10) pieces per year.
Tantalum capacitor
Due to their relatively high price, wet tantalum electrolytic capacitors have few consumer applications. They are used in ruggedized industrial applications, such as in probes for oil exploration. Types with military approvals can provide the extended capacitance and voltage ratings, along with the high quality levels required for avionics, military, and space applications.
Electrolytic capacitor
Aluminum electrolytic capacitors form the bulk of the electrolytic capacitors used in electronics because of the large diversity of sizes and the inexpensive production. Tantalum electrolytic capacitors, usually used in the SMD version, have a higher specific capacitance than the aluminum electrolytic capacitors and are used in devices with limited space or flat design such as laptops. They are also used in military technology, mostly in axial style, hermetically sealed. Niobium electrolytic chip capacitors are a new development in the market and are intended as a replacement for tantalum electrolytic chip capacitors.
RL circuit
In practice, however, capacitors (and RC circuits) are usually preferred to inductors since they can be more easily manufactured and are generally physically smaller, particularly for higher values of components.
Capacitor types
Supercapacitors are rarely interchangeable, especially those with higher energy densities. IEC standard 62391-1 "Fixed electric double layer capacitors for use in electronic equipment" identifies four application classes:
Applications of capacitors
Motor-starting capacitors are typically non-polarized electrolytic types, while running capacitors are conventional paper or plastic film dielectric types.
Supercapacitor
Since capacitors' energy content increases with the square of the voltage, researchers were looking for a way to increase the electrolyte's breakdown voltage. In 1994 using the anode of a 200V high voltage tantalum electrolytic capacitor, David A. Evans developed an "Electrolytic-Hybrid Electrochemical Capacitor". These capacitors combine features of electrolytic and electrochemical capacitors. They combine the high dielectric strength of an anode from an electrolytic capacitor with the high capacitance of a pseudocapacitive metal oxide (ruthenium (IV) oxide) cathode from an electrochemical capacitor, yielding a hybrid electrochemical capacitor. Evans' capacitors, coined Capattery, had an energy content about a factor of 5 higher than a comparable tantalum electrolytic capacitor of the same size. Their high costs limited them to specific military applications.
Rectifier
Typically these rectifiers were made up of stacks of metal plates or washers, held together by a central bolt, with the number of stacks determined by voltage; each cell was rated for about 20 V. An automotive battery charger rectifier might have only one cell: the high-voltage power supply for a vacuum tube might have dozens of stacked plates. Current density in an air-cooled selenium stack was about 600 mA per square inch of active area (about 90 mA per square centimeter).
Silicon diodes are the most widely used rectifiers for lower voltages and powers, and have largely replaced other rectifiers. Due to their substantially lower forward voltage (0.3V versus 0.7V for silicon diodes) germanium diodes have an inherent advantage over silicon diodes in low voltage circuits.
Capacitor types
Capacitors made by twisting 2 pieces of insulated wire together are called gimmick capacitors.
Gimmick capacitors were used in commercial and amateur radio receivers.Variable capacitors may have their capacitance changed by mechanical motion. Generally two versions of variable capacitors has to be to distinguishedVariable capacitors include capacitors that use a mechanical construction to change the distance between the plates, or the amount of plate surface area which overlaps. They mostly use air as dielectric medium.
Applications of capacitors
5.Signal processing.
The energy stored in capacitor can be used to represent information, either in binary form, as in DRAMs, or in analogue form, as in analog sampled filters and Charge-coupled device CCDs. Capacitors can be used in analog circuits as components of integrators or more complex filters and in negative feedback loop stabilization. Signal processing circuits also use capacitors to integrate a current signal.
Capacitor types
An AC load only can be applied to a non-polarized capacitor. Capacitors for AC applications are primarily film capacitors, metallized paper capacitors, ceramic capacitors and bipolar electrolytic capacitors.
Capacitor
Some old, large oil-filled paper or plastic film capacitors contain polychlorinated biphenyls (PCBs). It is known that waste PCBs can leak into groundwater under landfills. Capacitors containing PCB were labelled as containing "Askarel" and several other trade names. PCB-filled paper capacitors are found in very old (pre-1975) fluorescent lamp ballasts, and other applications.
Niobium capacitor
Tantalum electrolytic capacitors with solid electrolyte as surface-mountable chip capacitors are mainly used in electronic devices in which little space is available or a low profile is required. They operate reliable over a wide temperature range without large parameter deviations.
Capacitor types
Capacitors, together with resistors, and inductors, belong to the group of "passive components" used in electronic equipment. Although, in absolute figures, the most common capacitors are integrated capacitors (e.g. in DRAMs or flash memory structures), this article is concentrated on the various styles of capacitors as discrete components.
Capacitor
Motor-starting capacitors are typically non-polarized electrolytic types, while running capacitors are conventional paper or plastic film dielectric types.
Aluminum electrolytic capacitor
The first common application of wet aluminum electrolytic capacitors was in large telephone exchanges, to reduce relay hash (noise) on the 48 volt DC power supply. The development of AC-operated domestic radio receivers in the late 1920s created a demand for large-capacitance (for the time) and high-voltage capacitors for the valve amplifier technique, typically at least 4 microfarads and rated at around 500 volts DC. Waxed paper and oiled silk film capacitors were available, but devices with that order of capacitance and voltage rating were bulky and prohibitively expensive.
Capacitor
A capacitor can store electric energy when disconnected from its charging circuit, so it can be used like a temporary battery, or like other types of rechargeable energy storage system. Capacitors are commonly used in electronic devices to maintain power supply while batteries are being changed. (This prevents loss of information in volatile memory.)
Ceramic capacitor
In many applications of capacitors dielectric absorption is not a problem but in some applications, such as long-time-constant integrators, sample-and-hold circuits, switched-capacitor analog-to-digital converters and very low-distortion filters, it is important that the capacitor does not recover a residual charge after full discharge, and capacitors with low absorption are specified. The voltage at the terminals generated by dielectric absorption may in some cases possibly cause problems in the function of an electronic circuit or can be a safety risk to personnel. In order to prevent shocks, most very large capacitors like power capacitors are shipped with shorting wires that are removed before use.
Capacitor
Electrolytic capacitors use an aluminum or tantalum plate with an oxide dielectric layer. The second electrode is a liquid electrolyte, connected to the circuit by another foil plate. Electrolytic capacitors offer very high capacitance but suffer from poor tolerances, high instability, gradual loss of capacitance especially when subjected to heat, and high leakage current. Poor quality capacitors may leak electrolyte, which is harmful to printed circuit boards. The conductivity of the electrolyte drops at low temperatures, which increases equivalent series resistance. While widely used for power-supply conditioning, poor high-frequency characteristics make them unsuitable for many applications. Electrolytic capacitors suffer from self-degradation if unused for a period (around a year), and when full power is applied may short circuit, permanently damaging the capacitor and usually blowing a fuse or causing failure of rectifier diodes. For example, in older equipment, this may cause arcing in rectifier tubes. They can be restored before use by gradually applying the operating voltage, often performed on antique vacuum tube equipment over a period of thirty minutes by using a variable transformer to supply AC power. The use of this technique may be less satisfactory for some solid state equipment, which may be damaged by operation below its normal power range, requiring that the power supply first be isolated from the consuming circuits. Such remedies may not be applicable to modern high-frequency power supplies as these produce full output voltage even with reduced input.
Dielectric
Commercially manufactured capacitors typically use a solid dielectric material with high permittivity as the intervening medium between the stored positive and negative charges. This material is often referred to in technical contexts as the "capacitor dielectric".
Inductor
Inductors are used extensively in analog circuits and signal processing. Applications range from the use of large inductors in power supplies, which in conjunction with filter capacitors remove ripple which is a multiple of the mains frequency (or the switching frequency for switched-mode power supplies) from the direct current output, to the small inductance of the ferrite bead or torus installed around a cable to prevent radio frequency interference from being transmitted down the wire. Inductors are used as the energy storage device in many switched-mode power supplies to produce DC current. The inductor supplies energy to the circuit to keep current flowing during the "off" switching periods and enables topographies where the output voltage is higher than the input voltage.
Memory cell (computing)
Over the history of computing many different memory cell architectures have been used including core memory and bubble memory, but the most common ones used are flip-flops and capacitors.
Capacitor
Groups of large, specially constructed, low-inductance high-voltage capacitors ("capacitor banks") are used to supply huge pulses of current for many pulsed power applications. These include electromagnetic forming, Marx generators, pulsed lasers (especially TEA lasers), pulse forming networks, radar, fusion research, and particle accelerators.
Solid
A dielectric, or electrical insulator, is a substance that is highly resistant to the flow of electric current. A dielectric, such as plastic, tends to concentrate an applied electric field within itself, which property is used in capacitors. A capacitor is an electrical device that can store energy in the electric field between a pair of closely spaced conductors (called 'plates'). When voltage is applied to the capacitor, electric charges of equal magnitude, but opposite polarity, build up on each plate. Capacitors are used in electrical circuits as energy-storage devices, as well as in electronic filters to differentiate between high-frequency and low-frequency signals.
Decoupling capacitor
Since capacitors differ in their high-frequency characteristics (and capacitors with good high-frequency properties are often types with small capacity, while large capacitors usually have worse high-frequency response), decoupling often involves the use of a combination of capacitors. For example in logic circuits, a common arrangement is ~100 nF ceramic per logic IC (multiple ones for complex ICs), combined with electrolytic or tantalum capacitor(s) up to a few hundred μF per board or board section.
Ceramic capacitor
Power ceramic capacitors are mostly specified for much higher than 200 volt-amps. The great plasticity of ceramic raw material and the high dielectric strength of ceramics deliver solutions for many applications and are the reasons for the enormous diversity of styles within the family of power ceramic capacitors. These power capacitors have been on the market for decades. They are produced according to the requirements as class 1 power ceramic capacitors with high stability and low losses or class 2 power ceramic capacitors with high volumetric efficiency.
Tantalum capacitor
The required capacitance tolerance is determined by the particular application. Electrolytic capacitors, which are often used for filtering and bypassing capacitors don’t have the need for narrow tolerances because they are mostly not used for accurate frequency applications like oscillators.
Capacitive power supply
A capacitive power supply, also called a capacitive dropper, is a type of power supply that uses the capacitive reactance of a capacitor to reduce the mains voltage to a lower voltage. There are two important limitations: First, the high withstanding voltage required of the capacitor, along with the high-capacitance required for a given output current, mean that this type of supply is generally used only in low-power applications. (Generally, a capacitor of a given size or budget can have a high voltage rating or high capacitance, but not both.) The second is that due to the absence of electrical isolation, the circuit must be encapsulated and isolated to avoid direct (galvanic) contact with the users.
Rechargeable battery
Ultracapacitors are being developed for transportation, using a large capacitor to store energy instead of the rechargeable battery banks used in hybrid vehicles. One drawback of capacitors compared to batteries is that the terminal voltage drops rapidly; a capacitor that has 25% of its initial energy left in it will have one-half of its initial voltage. By contrast, battery systems tend to have a terminal voltage that does not decline rapidly until nearly exhausted. The undesirable characteristic complicates the design of power electronics for use with ultracapacitors. However, there are potential benefits in cycle efficiency, lifetime, and weight compared with rechargeable systems. China started using ultracapacitors on two commercial bus routes in 2006; one of them is route 11 in Shanghai.
Film capacitor
The most important advantages of film capacitors are the stability of their electrical values over long durations, their reliability, and lower cost than some other types for the same applications. Especially for applications with high current pulse loads or high AC loads in electrical systems, heavy-duty film capacitors, here called "power capacitors", are available with dielectric ratings of several kilovolts.
Filter capacitor
Filter capacitors are capacitors used for filtering of undesirable frequencies. They are common in electrical and electronic equipment, and cover a number of applications, such as:
Capacitor types
Electrolytic capacitors for special applications include motor start capacitors, flashlight capacitors and audio frequency capacitors.
Capacitor types
The types of capacitors used for power applications have a specified rated value for maximum ripple current. These are primarily aluminum electrolytic capacitors, and tantalum as well as some film capacitors and Class 2 ceramic capacitors.
Electrolytic capacitor
The non-solid or so-called "wet" aluminum electrolytic capacitors were and are the cheapest among all other conventional capacitors. They not only provide the cheapest solutions for high capacitance or voltage values for decoupling and buffering purposes but are also insensitive to low ohmic charging and discharging as well as to low-energy transients. Non-solid electrolytic capacitors can be found in nearly all areas of electronic devices, with the exception of military applications.
Tantalum
The major use for tantalum, as the metal powder, is in the production of electronic components, mainly capacitors and some high-power resistors. Tantalum electrolytic capacitors exploit the tendency of tantalum to form a protective oxide surface layer, using tantalum powder, pressed into a pellet shape, as one "plate" of the capacitor, the oxide as the dielectric, and an electrolytic solution or conductive solid as the other "plate". Because the dielectric layer can be very thin (thinner than the similar layer in, for instance, an aluminium electrolytic capacitor), a high capacitance can be achieved in a small volume. Because of the size and weight advantages, tantalum capacitors are attractive for portable telephones, personal computers, automotive electronics and cameras.
Coltan
Coltan is used primarily for the production of tantalum capacitors, used in many electronic devices. Many sources mention coltan's importance in the production of mobile phones, but tantalum capacitors are used in almost every kind of electronic device. Niobium and tantalum have a wide range of uses, including refractive lenses for glasses, cameras, phones and printers. They are also used in semiconductor circuits, and capacitors for small electronic devices such as hearing aids, pacemakers, and mp3 players, as well as in computer hard drives, automobile electronics, and surface acoustic wave (SAW) filters for mobile phones.
Ceramic capacitor
The tests and requirements to be met by ceramic capacitors for use in electronic equipment for approval as standardized types are set out in the following sectional specifications:Multilayer ceramic capacitors are increasingly used to replace tantalum and low capacitance aluminium electrolytic capacitors in applications such as bypass or high frequency switched-mode power supplies as their cost, reliability and size becomes competitive. In many applications, their low ESR allows the use of a lower nominal capacitance value.
Film capacitor
Polypropylene film capacitors meet the criteria for stability Class 1 capacitors, and have low electrical losses and nearly linear behavior over a very wide temperature and frequency range. They are used for oscillators and resonant circuits; for electronic filter applications with high quality factor (Q) such as high-pass filters, low-pass filters and band-pass filters as well as for tuning circuits; for audio crossovers in loudspeakers; in sample and hold A/D converters and in peak voltage detectors. Tight capacitance tolerances are required for timing applications in signal lights or pulse width generators to control the speed of motors, PP film capacitors are also well-suited because of their very low leakage current.
Film capacitor
As of 2012, only five plastic materials continued to be widely used in the capacitor industry as films for capacitors: PET, PEN, PP, PPS and PTFE. Other plastic materials are no longer in common use, either because they are no longer manufactured, or they have been replaced with better materials. Even the long-time manufactured polystyrene (PS) and polycarbonate (PC) film capacitors have been largely replaced by the previously-mentioned film types, though at least one PC capacitor manufacturer retains the ability to make its own films from raw polycarbonate feedstock. The less-common plastic films are described briefly here, since they are still encountered in older designs, and are still available from some suppliers.
Applications of capacitors
High-voltage capacitors can benefit from a pre-charge to limit in-rush currents at power-up of high voltage direct current (HVDC) circuits. This will extend the life off the component and may mitigate high-voltage hazards.
Refractory metals
Many important uses have been found for tantalum owing to this property, particularly in the medical and surgical fields, and also in harsh acidic environments. It is also used to make superior electrolytic capacitors. Tantalum films provide the second most capacitance per volume of any substance after Aerogel, and allow miniaturization of electronic components and circuitry. Many cellular phones and computers contain tantalum capacitors.
Applications of capacitors
Groups of large, specially constructed, low-inductance high-voltage capacitors ("capacitor banks") are used to supply huge pulses of current for many pulsed power applications. These include electromagnetic forming, Marx generators, pulsed lasers (especially TEA lasers), pulse forming networks, fusion research, and particle accelerators.
Polymer capacitor
These capacitors were used in devices for applications that required the lowest possible ESR or highest possible ripple current. One OS-CON e-cap could replace three more bulky "wet" e-caps or two Ta-caps. By 1995, the Sanyo OS-CON became the preferred decoupling capacitor for Pentium processor-based IBM personal computers.
The Sanyo OS-CON e-cap product line was sold in 2010 to Panasonic. Panasonic then replaced the TCNQ salt with a conducting polymer under the same brand.
Film capacitor
These capacitors have a low dissipation factor and because of their relatively temperature-independent electrical properties of about ±80 ppm over the entire temperature range, they had many applications for low-loss and temperature-stable applications such as timing circuits, precision analog circuits, and signal filters in applications with tough environmental conditions. PC film capacitors had been manufactured since the mid-1950s, but the main supplier of polycarbonate film for capacitors had ceased the production of this polymer in film form as of the year 2000. As a result, most of the manufacturers of polycarbonate film capacitors worldwide had to stop their production of PC film capacitors and changed to polypropylene film capacitors instead. Most of the former PC capacitor applications have found satisfactory substitutes with PP film capacitors.
Comparator
The most frequent application for comparators is the comparison between a voltage and a stable reference. Most comparator manufacturers also offer comparators in which a reference voltage is integrated on to the chip. Combining the reference and comparator in one chip not only saves space, but also draws less supply current than a comparator with an external reference. ICs with wide range of references are available such as MAX9062 (200 mV reference), LT6700 (400 mV reference), ADCMP350 (600 mV reference), MAX9025 (1.236 V reference), MAX9040 (2.048 V reference), TLV3012 (1.24 V reference) and TSM109 (2.5 V reference).
Capacitor
Most of the plastic films now used offer better stability and ageing performance than such older dielectrics such as oiled paper, which makes them useful in timer circuits, although they may be limited to relatively low operating temperatures and frequencies, because of the limitations of the plastic film being used. Large plastic film capacitors are used extensively in suppression circuits, motor start circuits, and power factor correction circuits.
Capacitor
Practical capacitors are available commercially in many different forms. The type of internal dielectric, the structure of the plates and the device packaging all strongly affect the characteristics of the capacitor, and its applications.
Supercapacitor
Supercapacitors are used in applications requiring many rapid charge/discharge cycles rather than long term compact energy storage: within cars, buses, trains, cranes and elevators, where they are used for regenerative braking, short-term energy storage or burst-mode power delivery. Smaller units are used as memory backup for static random-access memory (SRAM).
Film capacitor
Historically, the first “film” type capacitors were paper capacitors of film/foil configuration. They were fairly bulky, and not particularly reliable. As of 2012, paper is used in the form of metallized paper for MP capacitors with self-healing properties used for EMI suppression. Paper is also used as an insulating mechanical carrier of metallized-layer electrodes, and combined with polypropylene dielectric, mostly in power capacitors rated for high current AC and high voltage DC applications.
Film capacitor
Most power capacitors, the largest capacitors made, generally use polypropylene film as the dielectric. PP film capacitors are used for high-frequency high-power applications such as induction heating, for pulsed power energy discharge applications, and as AC capacitors for electrical distribution. The AC voltage ratings of these capacitors can range up to 400 kV.
Aluminum electrolytic capacitor
In general, a capacitor is seen as a storage component for electric energy. But this is only one capacitor function. A capacitor can also act as an AC resistor. Especially aluminum electrolytic capacitors are used in many applications as a decoupling capacitors to filter or bypass undesired biased AC frequencies to the ground or for capacitive coupling of audio AC signals. Then the dielectric is used only for blocking DC. For such applications the AC resistance, the impedance is as important as the capacitance value.
Electrolytic capacitor
The large capacitance of electrolytic capacitors makes them particularly suitable for passing or bypassing low-frequency signals, and for storing large amounts of energy. They are widely used for decoupling or noise filtering in power supplies and DC link circuits for variable-frequency drives, for coupling signals between amplifier stages, and storing energy as in a flashlamp.
Applications of capacitors
A decoupling capacitor is a capacitor used to decouple one part of a circuit from another. Noise caused by other circuit elements is shunted through the capacitor, reducing the effect they have on the rest of the circuit. It is most commonly used between the power supply and ground.
An alternative name is "bypass capacitor" as it is used to bypass the power supply or other high impedance component of a circuit.
Capacitor types
Aluminium electrolytic capacitors, the most common type for power supplies, experience shorter life expectancy at higher ripple currents. Exceeding the limit tends to result in explosive failure.
Energy storage
Supercapacitors bridge the gap between conventional capacitors and rechargeable batteries. 
They store the most energy per unit volume or mass (energy density) among capacitors. They support up to 10,000 farads/1.2 volt, up to 10,000 times that of electrolytic capacitors, but deliver or accept less than half as much power per unit time (power density).
Water capacitor
Although the design and materials used in capacitors have changed greatly throughout history, the basic fundamentals remain the same. In general, capacitors are very simple electrical devices which can have many uses in today's technologically advanced world. A modern capacitor usually consists of two conducting plates sandwiched around an insulator. Electrical researcher Nicola Tesla described capacitors as the "electrical equivalent of dynamite".
Capacitor
Reservoir capacitors are used in power supplies where they smooth the output of a full or half wave rectifier. They can also be used in charge pump circuits as the energy storage element in the generation of higher voltages than the input voltage.
Varicap
Varactors are used as voltage-controlled capacitors. They are commonly used in voltage-controlled oscillators, parametric amplifiers, and frequency multipliers. Voltage-controlled oscillators have many applications such as frequency modulation for FM transmitters and phase-locked loops. Phase-locked loops are used for the frequency synthesizers that tune many radios, television sets, and cellular telephones.
Supercapacitor
In applications with fluctuating loads, such as laptop computers, PDA's, GPS, portable media players, hand-held devices, and photovoltaic systems, supercapacitors can stabilize the power supply.
Applications of capacitors
Capacitors and inductors are applied together in tuned circuits to select information in particular frequency bands. For example, radio receivers rely on variable capacitors to tune the station frequency. Speakers use passive analog crossovers, and analog equalizers use capacitors to select different audio bands.
Capacitor
However, low value capacitors are available with a vacuum between their plates to allow extremely high voltage operation and low losses. Variable capacitors with their plates open to the atmosphere were commonly used in radio tuning circuits. Later designs use polymer foil dielectric between the moving and stationary plates, with no significant air space between the plates.
Energy storage
A capacitor (originally known as a 'condenser') is a passive two-terminal electrical component used to store energy electrostatically. Practical capacitors vary widely, but all contain at least two electrical conductors (plates) separated by a dielectric (i.e., insulator). A capacitor can store electric energy when disconnected from its charging circuit, so it can be used like a temporary battery, or like other types of rechargeable energy storage system. Capacitors are commonly used in electronic devices to maintain power supply while batteries change. (This prevents loss of information in volatile memory.) Conventional capacitors provide less than 360 joules per kilogram, while a conventional alkaline battery has a density of 590 kJ/kg.