A capacitor is an electrical/electronic device that can store energy in the electric field between a pair of conductors (called "plates"). A capacitor is a passive electrical component that can store Energy in the Electric field between a pair of conductors In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός In Physics, the space surrounding an Electric charge or in the presence of a time-varying Magnetic field has a property called an electric field (that can In Science and engineering, a conductor is a material which contains movable Electric charges. The process of storing energy in the capacitor is known as "charging", and involves electric charges of equal magnitude, but opposite polarity, building up on each plate. Electric charge is a fundamental conserved property of some Subatomic particles which determines their Electromagnetic interaction.

Capacitors are often used in electric and electronic circuits as energy-storage devices. An electrical network is an interconnection of Electrical elements such as Resistors Inductors Capacitors Transmission lines Voltage Energy storage is the storing of some form of Energy that can be drawn upon at a later time to perform some useful operation They can also be used to differentiate between high-frequency and low-frequency signals. Frequency is a measure of the number of occurrences of a repeating event per unit Time. In the fields of communications, Signal processing, and in Electrical engineering more generally a signal is any time-varying or spatial-varying quantity This property makes them useful in electronic filters. Electronic filters are Electronic circuits which perform Signal processing functions specifically intended to remove unwanted signal components and/or enhance wanted

Capacitors are occasionally referred to as condensers. This is considered an antiquated term in English, but most other languages use an equivalent, like "condensateur" in French, "Kondensator" in German, "condensatore" in Italian, "condensador" in Spanish, or "Kondensa" in Japanese.

Contents 1 History 2 Theory of operation 2.1 Capacitance 2.2 Energy storage 2.3 Hydraulic analogy 2.4 Aging 3 Electric circuits 3.1 DC sources 3.2 AC sources 3.2.1 Impedance 3.2.2 Laplace equivalent (s-domain) 3.3 Displacement current 3.4 Networks 3.4.1 Series or parallel arrangements 3.5 Capacitor/inductor duality 4 Capacitor types 4.1 Dielectric materials 4.2 Structure 5 Applications 5.1 Energy storage 5.2 Power conditioning 5.2.1 Power factor correction 5.3 Filtering 5.3.1 Signal coupling 5.3.2 Decoupling 5.3.3 Noise filters, motor starters, and snubbers 5.4 Signal processing 5.4.1 Tuned circuits 5.5 Other applications 5.5.1 Sensing 5.5.2 Pulsed power and weapons 6 Hazards and safety 6.1 High voltage 7 See also 8 Notes 9 References 10 External links

History

In October 1745, Ewald Georg von Kleist of Pomerania in Germany invented the first recorded capacitor: a glass jar with water inside as one plate was held on the hand as the other plate. Ewald Georg (or Jürgen von Kleist ( 10 June 1700 &ndash December 11, 1748) was a German Jurist, Lutheran cleric Germany, officially the Federal Republic of Germany ( ˈbʊndəsʁepuˌbliːk ˈdɔʏtʃlant is a Country in Central Europe. A wire in the mouth of the bottle received charge from an electric machine, and released it as a spark. ^[1]

In the same year, Dutch physicist Pieter van Musschenbroek independently invented a very similar capacitor. Pieter (Petrus van Musschenbroek ( 14 March 1692, Leiden - 19 September 1761, Leiden was a Dutch scientist who is credited It was named the Leyden jar, after the University of Leyden where van Musschenbroek worked. The Leyden jar is a simple device that "stores" static electricity in large amounts Leiden University (Universiteit Leiden located in the city of Leiden, is the oldest University in The Netherlands. Daniel Gralath was the first to combine several jars in parallel into a "battery" to increase the charge storage capacity.

Benjamin Franklin investigated the Leyden jar, and proved that the charge was stored on the glass, not in the water as others had assumed. Benjamin Franklin ( April 17 1790 was one of the Founding Fathers of the United States of America. The Leyden jar is a simple device that "stores" static electricity in large amounts The earliest unit of capacitance was the 'jar', equivalent to about 1 nanofarad. This is about the capacitance unit of measure For the charge unit see Faraday (unit.

Early capacitors were also known as condensers, a term that is still occasionally used today. It was coined by Alessandro Volta in 1782 (derived from the Italian condensatore), with reference to the device's ability to store a higher density of electric charge than a normal isolated conductor. Count Alessandro Giuseppe Antonio Anastasio Volta was a Lombard physicist known especially for the development of the first electric cell in Most non-English European languages still use a word derived from "condensatore".

Theory of operation

A capacitor consists of two conductive electrodes, or plates, separated by a dielectric, which prevents charge from moving directly between the plates. An electrode is an Electrical conductor used to make contact with a nonmetallic part of a circuit (e A dielectric is a nonconducting substance ie an insulator. The term was coined by William Whewell in response to a request from Michael Faraday. Charge may however be moved indirectly by external influences, such as a battery connecting the terminals. After removing the external influences, the charge on the plates persists. The separated charges attract each other, and an electric field is present between the plates. ---- Bold text Coulomb's law', developed in the 1780s by French physicist Charles Augustin de Coulomb, may be stated in scalar form In Physics, the space surrounding an Electric charge or in the presence of a time-varying Magnetic field has a property called an electric field (that can The simplest practical capacitor consists of two wide, flat, parallel plates separated by a thin dielectric layer.

Assuming that the area of the plates A is much greater than their separation d, the instantaneous electric field between the plates E(t) is identical at any location away from the edges. If the instantaneous charge on a plate − q(t) is spread evenly,

,

where is the permittivity of the dielectric. Permittivity is a Physical quantity that describes how an Electric field affects and is affected by a Dielectric medium and is determined by the ability The voltage v(t) between the plates is given by

,

where z is a position between the plates

Capacitance

A property called the capacitance C, which is a measure of the charge stored on each plate for a given voltage such that

q(t) = Cv(t),

where

for an ideal parallel plate capacitor. Capacitance is a measure of the amount of Electric charge stored (or separated for a given Electric potential. Electric charge is a fundamental conserved property of some Subatomic particles which determines their Electromagnetic interaction.

In SI units, a capacitor has a capacitance of one farad when one coulomb of charge storage corresponds to one volt between its plates. This is about the capacitance unit of measure For the charge unit see Faraday (unit. The coulomb (symbol C) is the SI unit of Electric charge. It is named after Charles-Augustin de Coulomb. The volt (symbol V) is the SI derived unit of electric Potential difference or Electromotive force. Since the farad is a very large unit, capacitance is usually expressed in microfarads (µF), nanofarads (nF), or picofarads (pF). In general, capacitance is greater in devices with large plate areas, separated by small distances. When a dielectric is present between two charged plates, its molecules become polarized and reduce the internal electric field and hence the voltage. Polarization ( ''Brit'' polarisation) is a property of Waves that describes the orientation of their oscillations The capacitance is therefore strongly dependent on the quality of the dielectric.

Energy storage

Work must be done by an external influence to move charge between the plates in a capacitor. In Thermodynamics, work is the quantity of Energy transferred from one system to another without an accompanying transfer of Entropy. When the external influence is removed, the charge separation persists and energy is stored in the electric field. In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός If charge is later allowed to return to its equilibrium position, the energy is released. The work done in establishing the electric field, and hence the amount of energy stored, is given by

The maximum energy that can be stored safely in a capacitor is limited by the breakdown voltage of the dielectric. Breakdown Voltage of an Insulator is the minimum voltage that causes a portion of an insulator to become electrically conductive. Therefore, all capacitors made with a particular dielectric have approximately identical maximum energy density if the dielectric dominates their volume. Energy density is the amount of Energy stored in a given system or region of space per unit Volume, or per unit Mass, depending on the context although

Hydraulic analogy

Main article: Hydraulic analogy

As electrical circuitry can be modeled by fluid flow, a capacitor can be modeled as a chamber with a flexible diaphragm separating the input from the output. The electronic&ndash hydraulic analogy (derisively referred to as the drain-pipe theory by Oliver Heaviside) is the most widely used analogy for "electron fluid" Fluid dynamics is the sub-discipline of Fluid mechanics dealing with fluid flow: Fluids ( Liquids and Gases in motion A diaphragm seal is a flexible membrane that seals and isolates an enclosure As can be determined intuitively as well as mathematically, this provides the correct characteristics:

• The pressure difference (voltage difference) across the unit is proportional to the integral of the flow (current). Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface
• A steady state current cannot pass through it because the pressure will build up across the diaphragm until it equally opposes the source pressure,
• but a transient pulse or alternating current can be transmitted. Steady state is a more general situation than Dynamic equilibrium.
• An overpressure results in bursting of the diaphragm, analogous to dielectric breakdown.
• The capacitance of units connected in parallel is equivalent to the sum of their individual capacitances.

Aging

The capacitance of certain capacitors decreases as the component ages. In ceramic capacitors, this is caused by degradation of the dielectric. The type of dielectric and the ambient operating and storage temperatures are the most significant aging factors, while the operating voltage has a smaller effect. The aging process may be reversed by heating the component above the Curie point. The Curie point ( Tc) or Curie temperature, is a term in Physics and Materials science, named after Pierre Curie (1859-1906 Aging is fastest near the beginning of life of the component, and the device stabilizes over time. ^[2] Electrolytic capacitors age as the electrolyte evaporates. An electrolytic capacitor is a type of Capacitor that uses an ionic conducting liquid as one of its plates In contrast with ceramic capacitors, this occurs towards the end of life of the component.

Electric circuits

When a capacitor is connected to a current source, charge is transfered between its plates at a rate i(t) = dq(t) / dt. As the voltage between the plates is proportional to the charge, it follows that

.

Conversely, if a capacitor is connected to a voltage source, the resulting current is

DC sources

A circuit containing only a resistor, a capacitor, a switch and a constant (DC) voltage source v_src(t) = V₀ in series is known as a charging circuit. |- align = "center"| |width = "25"| | |- align = "center"| || Potentiometer |- align = "center"| | | |- align = "center"| Resistor| | From Kirchhoff's voltage law it follows that

,

where v_r(t) and v_c(t) are the voltages across the resistor and capacitor respectively. For other laws named after Gustav Kirchhoff, see Kirchhoff's laws. This reduces to a first order differential equation

Assuming that the capacitor is initially uncharged, there is no internal electric field, and the initial current is I₀ = V₀ / R. This initial condition allows solution of the differential equation as

.

The corresponding voltage drop across the capacitor is

.

Therefore, as charge increases on the capacitor plates, the voltage across the capacitor increases, until it reaches a steady-state value of V₀, and the current drops to zero. Both the current, and the difference between the source and capacitor voltage decay exponentially with respect to time. The time constant of the decay is given by τ = RC. In Physics and Engineering, the time constant usually denoted by the Greek letter \tau, (tau characterizes the Frequency

AC sources

When connected to an alternating current (AC) voltage source, the plates on a capacitor repeatedly charge and discharge relative to each other. An alternating current ( AC) is an Electric current whose direction reverses cyclically as opposed to Direct current, whose direction remains constant The current varies sinusoidally, with a nonzero amplitude. Amplitude is the magnitude of change in the oscillating variable with each Oscillation, within an oscillating system For this reason, capacitors effectively conduct AC although charge ideally never passes directly through the dielectric. Since the current is proportional to the time derivative of the voltage, a sinusoidal current leads the voltage by a 90 degree phase shift, or equivalently a quarter cycle. The amplitude of the voltage depends on the amplitude of the current divided by the product of the frequency of the current with the capacitance, C.

Impedance

The ratio of the phasor voltage across a circuit element to the phasor current through that element is called the impedance Z. In Physics and Engineering, a phase vector ("phasor" is a representation of a Sine wave whose amplitude ( A) phase ( θ) Electrical impedance, or simply impedance, describes a measure of opposition to a sinusoidal Alternating current (AC For a capacitor, the impedance is given by

where is the capacitive reactance, is the angular frequency, f is the frequency), C is the capacitance in farads, and j is the imaginary unit. Do not confuse with Angular velocity In Physics (specifically Mechanics and Electrical engineering) angular frequency Frequency is a measure of the number of occurrences of a repeating event per unit Time. Definition By definition the imaginary unit i is one solution (of two of the Quadratic equation

While this relation (between the frequency domain voltage and current associated with a capacitor) is always true, the ratio of the time domain voltage and current amplitudes is equal to X_C only for sinusoidal (AC) circuits in steady state.

See derivation Deriving capacitor impedance.

Hence, capacitive reactance is the negative imaginary component of impedance. The negative sign indicates that the current leads the voltage by 90° for a sinusoidal signal, as opposed to the inductor, where the current lags the voltage by 90°.

The impedance is analogous to the resistance of a resistor. Electrical resistance is a ratio of the degree to which an object opposes an Electric current through it measured in Ohms Its reciprocal quantity is |- align = "center"| |width = "25"| | |- align = "center"| || Potentiometer |- align = "center"| | | |- align = "center"| Resistor| | The impedance of a capacitor is inversely proportional to the frequency - that is, for very high-frequency alternating currents the reactance approaches zero - so that a capacitor is nearly a short circuit to a very high frequency AC source. This article is about proportionality the mathematical relation Short Circuit is a 1986 comedy Science fiction film starring Ally Sheedy and Steve Guttenberg and directed by Conversely, for very low frequency alternating currents, the reactance increases without bound so that a capacitor is nearly an open circuit to a very low frequency AC source. This frequency dependent behaviour accounts for most uses of the capacitor (see "Applications", below).

Reactance is so called because the capacitor does not dissipate power, but merely stores energy. In electrical circuits, as in mechanics, there are two types of load, resistive and reactive. Resistive loads (analogous to an object sliding on a rough surface) dissipate the energy delivered by the circuit as heat, while reactive loads (analogous to a spring or frictionless moving object) store this energy, ultimately delivering the energy back to the circuit.

Also significant is that the impedance is inversely proportional to the capacitance, unlike resistors and inductors for which impedances are linearly proportional to resistance and inductance respectively. This is why the series and shunt impedance formulae (given below) are the inverse of the resistive case. In series, impedances sum. In parallel, conductances sum.

Laplace equivalent (s-domain)

When using the Laplace transform in circuit analysis, the capacitive impedance is represented in the s domain by:

where C is the capacitance, and s (= σ+jω) is the complex frequency. In Mathematics, the Laplace transform is one of the best known and most widely used Integral transforms It is commonly used to produce an easily soluble algebraic

Displacement current

The physicist James Clerk Maxwell invented the concept of displacement current, dD/dt, to make Ampère's law consistent with conservation of charge in cases where charge is accumulating as in a capacitor. James Clerk Maxwell (13 June 1831 &ndash 5 November 1879 was a Scottish mathematician and theoretical physicist. Displacement current is a quantity that arises in a changing electric field He interpreted this as a real motion of charges, even in vacuum, where he supposed that it corresponded to motion of dipole charges in the aether. In physics there are two kinds of dipoles ( Hellènic: di(s- = two- and pòla = pivot hinge An electric dipole is a In the late 19th century " luminiferous aether " (or " ether " meaning light-bearing aether, was the term used to describe a medium for the propagation Although this interpretation has been abandoned, Maxwell's correction to Ampère's law remains valid.

Networks

Series or parallel arrangements

Main article: Series and parallel circuits

Capacitors in a parallel configuration each have the same potential difference (voltage). If two or more circuit components are connected end to end like a daisy chain it is said they are connected in series. If two or more circuit components are connected end to end like a daisy chain it is said they are connected in series. Their total capacitance (C_eq) is given by:

The reason for putting capacitors in parallel is to increase the total amount of charge stored. In other words, increasing the capacitance also increases the amount of energy that can be stored. Its expression is:

The current through capacitors in series stays the same, but the voltage across each capacitor can be different. If two or more circuit components are connected end to end like a daisy chain it is said they are connected in series. The sum of the potential differences (voltage) is equal to the total voltage. Their total capacitance is given by:

In parallel, the effective area of the combined capacitor has increased, increasing the overall capacitance. However, in series, the distance between the plates has effectively been increased, reducing the overall capacitance.

In practice capacitors will be placed in series as a means of economically obtaining very high voltage capacitors, for example for smoothing ripples in a high voltage power supply. Three "600 volt maximum" capacitors in series, will increase their overall working voltage to 1800 volts. This is of course offset by the capacitance obtained being only one third of the value of the capacitors used. This can be countered by connecting 3 of these series set-ups in parallel, resulting in a 3x3 matrix of capacitors with the same overall capacitance as an individual capacitor but operable under three times the voltage. In this application, a large resistor would be connected across each capacitor to ensure that the total voltage is divided equally across each capacitor and also to discharge the capacitors for safety when the equipment is not in use. |- align = "center"| |width = "25"| | |- align = "center"| || Potentiometer |- align = "center"| | | |- align = "center"| Resistor| |

Another application is for use of polarized capacitors in alternating current circuits; the capacitors are connected in series, in reverse polarity, so that at any given time one of the capacitors is not conducting.

Capacitor/inductor duality

In mathematical terms, the ideal capacitor can be considered as an inverse of the ideal inductor, because the voltage-current equations of the two devices can be transformed into one another by exchanging the voltage and current terms. An inductor is a passive electrical component designed to provide Inductance in a circuit Just as two or more inductors can be magnetically coupled to make a transformer, two or more charged conductors can be electrostatically coupled to make a capacitor. A transformer is a device that transfers Electrical energy from one circuit to another through inductively coupled Electrical conductors The mutual capacitance of two conductors is defined as the current that flows in one when the voltage across the other changes by unit voltage in unit time.

Capacitor types

Main article: capacitor (component)

Practical capacitors are available commercially in many different forms. Practical capacitors are often classified according to the material used as the dielectric with the dielectrics divided into two broad categories bulk insulators and metal-oxide 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.

Dielectric materials

Most types of capacitor include a dielectric spacer, which increases their capacitance. However, low capacitance devices are available with a vacuum between their plates, which allows extremely high voltage operation and low losses. This vacuum means "absence of matter" or "an empty area or space" for the cleaning appliance see Vacuum cleaner. Air filled variable capacitors are also commonly used in radio tuning circuits.

Several solid dielectrics are available, including paper, plastic, glass, mica and ceramic materials. Paper is thin material mainly used for writing upon printing upon or packaging Plastic is the general common term for a wide range of synthetic or semisynthetic organic solid materials suitable for the manufacture of industrial products Glass in the common sense refers to a Hard, Brittle, transparent Solid, such as that used for Windows many The word "mica" is thought to be derived from the Latin word la micare, "glitteren" in reference to the brilliant appearance of this mineral (especially The word ceramic is derived from the Greek word κεραμικός ( keramikos) Paper was used extensively in older devices and offers relatively high voltage performance. However, it is susceptible to water absorption, and has been largely replaced by plastic film capacitors. Plastics offer better stability and aging performance, which makes them useful in timer circuits, although they may be limited to low operating temperatures and frequencies. Ceramic capacitors are generally small, cheap and useful for high frequency applications, although their capacitance varies strongly with voltage, and they age poorly. They are broadly categorized as Class 1 dielectrics, which have predictable variation of capacitance with temperature or Class 2 dielectrics, which can operate at higher voltage. The EIA Class 1 dielectric materials are Ceramic Dielectric materials used in ceramic capacitors of small values (typically The EIA Class 2 dielectric materials are Ceramic Dielectric materials used in ceramic capacitors. Glass and mica capacitors are extremely reliable, stable and tolerant to high temperatures and voltages, but are too expensive for most mainstream applications.

Electrolytic capacitors use an aluminum or tantalum plate with an oxide dielectric layer. The second electrode is a liquid electrolyte. An electrolyte is any substance containing free Ions that behaves as an electrically conductive medium 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. The conductivity of the electrolyte drops at low temperatures, which increases equivalent series resistance. Equivalent series resistance (ESR is an effective resistance that is used to describe the resistive parts of the impedance of certain electrical components While widely used for power-supply conditioning, poor high-frequency characteristics make them unsuitable for many applications. Tantalum capacitors offer better frequency and temperature characteristics than aluminum, but higher dielectric absorption and leakage. ^[3] OS-CON (or OC-CON) capacitors are a polymerized organic semiconductor solid-electrolyte type that offer longer life at higher cost than standard electrolytic capacitors. OSCON or OS-CON Capacitors are a polymerized organic semiconductor solid-electrolyte device

Several other types of capacitor are available for specialist applications. Supercapacitors made from carbon aerogel, carbon nanotubes, or highly porous electrode materials offer extremely high capacity and can be used in some applications instead of rechargeable batteries. Electric double-layer capacitors, also known as supercapacitors, electrochemical double layer capacitors ( EDLCs) or ultracapacitors Aerogel is a low-density solid-state material derived from Gel in which the liquid component of the gel has been replaced with gas See also Rechargeable electricity storage system A rechargeable battery, also known as a storage battery, is a group of two or more secondary Alternating current capacitors are specifically designed to work on line (mains) voltage AC power circuits. An alternating current ( AC) is an Electric current whose direction reverses cyclically as opposed to Direct current, whose direction remains constant They are commonly used in electric motor circuits and are often designed to handle large currents, so they tend to be physically large. An electric motor uses Electrical energy to produce Mechanical energy. They are usually ruggedly packaged, often in metal cases that can be easily grounded/earthed. They also tend to have rather high direct current breakdown voltages. Direct current ( DC) is the unidirectional flow of Electric charge.

Structure

Capacitors may have their plates arranged in many configurations, for example axially or radially. Small, cheap discoidal ceramic capacitors have existed since the 1930s, and remain in widespread use. Since the 1980s, surface mount packages for capacitors have been widely used. Surface-mount technology ( SMT) is a method for constructing electronic circuits in which the components (SMC or Surface Mounted Components are mounted directly onto These packages are extremely small and lack connecting leads, allowing them to be soldered directly onto the surface of printed circuit boards. A printed circuit board, or PCB, is used to mechanically support and electrically connect Electronic components using conductive pathways or traces Surface mount components avoid undesirable high-frequency effects due to the leads and simplify automated assembly, although manual handling is made difficult due to their small size.

Variable capacitors are available in various forms. A variable capacitor is a Capacitor whose capacitance may be intentionally and repeatedly changed mechanically or electronically 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. Very cheap variable capacitors squeeze together alternating layers of aluminum and plastic with a screw, but the resulting capacitance is unstable, and unreproducible. A trimmer is a miniature adjustable electrical component It is meant to be set correctly when installed in some device and never seen or adjusted by the device's user Electrical control of capacitance is achievable with varactors (or varicaps), which are reverse-biased semiconductor diodes whose depletion region width varies with applied voltage. In Electronics, a varicap diode, varactor diode, variable capacitance diode or tuning diode is a type of Diode which has a variable Reverse-biased usually refers to how a Diode is used in a Circuit. Dioden2jpg|thumb|right|150px|Figure 2 Various semiconductor diodes In Semiconductor physics, the depletion region, also called depletion layer, depletion zone, junction region or the space charge region They are used in phase-locked loops, amongst other applications. A phase-locked loop or phase lock loop (PLL is a Control system that generates a signal that has a fixed relation to the phase of a "reference"

Applications

Capacitor symbols

Capacitor	Polarized capacitors	Variable capacitor

Capacitors have various uses in electronic and electrical systems.

Energy storage

A capacitor can store electric energy when disconnected from its charging circuit, so it can be used like a temporary battery. In electronics a battery is a combination of two or more Electrochemical cells which store chemical Energy which can be converted into electrical energy Capacitors are commonly used in electronic devices to maintain power supply while batteries are being changed. (This prevents loss of information in volatile memory. )

Power conditioning

Reservoir capacitors are used in power supplies where they smooth the output of a full or half wave rectifier. A reservoir capacitor is a Capacitor that is used to smooth the pulsating DC from an AC Rectifier. Power supply is a reference to a source of Electrical power. A device or system that supplies Electrical or other types of Energy to an output load A rectifier is an electrical device that converts Alternating current (AC to Direct current (DC a process known as rectification. They can also be used in charge pump circuits as the energy storage element in the generation of higher voltages than the input voltage. A charge pump is an Electronic circuit that uses Capacitors as energy storage elements to create either a higher or lower Voltage power source

Capacitors are connected in parallel with the power circuits of most electronic devices and larger systems (such as factories) to shunt away and conceal current fluctuations from the primary power source to provide a "clean" power supply for signal or control circuits. Audio equipment, for example, uses several capacitors in this way, to shunt away power line hum before it gets into the signal circuitry. The capacitors act as a local reserve for the DC power source, and bypass AC currents from the power supply. This is used in car audio applications, when a stiffening capacitor compensates for the inductance and resistance of the leads to the lead-acid car battery. Car audio/video (car AV is a term used to describe the sound or video system fitted in an Automobile. Lead-acid batteries, invented in 1859 by French Physicist Gaston Planté, are the oldest type of Rechargeable battery. A car battery is a type of Rechargeable battery that supplies electric energy to an Automobile.

Power factor correction

Capacitors are used in power factor correction. Such capacitors often come as three capacitors connected as a three phase load. This article deals with the basic mathematics and principles of three-phase electricity If an electric circuit has a well-defined output terminal the circuit connected to this terminal (or its Input impedance) is the load. Usually, the values of these capacitors are given not in farads but rather as a reactive power in volt-amperes reactive (VAr). This article deals with power in AC systems See Mains electricity for information on utility supplied AC power The purpose is to counteract inductive loading from electric motors and fluorescent lighting in order to make the load appear to be mostly resistive. An induction motor (IM is a type of asynchronous AC motor where power is supplied to the rotating device by means of electromagnetic induction. A fluorescent lamp or fluorescent tube is a Gas-discharge lamp that uses Electricity to excite mercury Vapor.

Filtering

Signal coupling

Main article: capacitive coupling

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. In Electronics, capacitive coupling is the transfer of energy within an Electrical network by means of the Capacitance between circuit nodes In the fields of communications, Signal processing, and in Electrical engineering more generally a signal is any time-varying or spatial-varying quantity 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.

Decoupling

Main article: decoupling capacitor

A decoupling capacitor is a capacitor used to decouple one part of a circuit from another. A decoupling capacitor is a Capacitor used to Decouple one part of an Electrical network (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.

Noise filters, motor starters, and snubbers

When an inductive circuit is opened, the current through the inductance collapses quickly, creating a large voltage across the open circuit of the switch or relay. If the inductance is large enough, the energy will generate a spark, causing the contact points to oxidize, deteriorate, or sometimes weld together, or destroying a solid-state switch. A snubber capacitor across the newly opened circuit creates a path for this impulse to bypass the contact points, thereby preserving their life; these were commonly found in contact breaker ignition systems, for instance. A snubber is a device used to suppress ("snub" voltage transients in electrical systems pressure transients in fluid systems or excess force or rapid movement in mechanical A contact breaker (or "points" is a type of electrical Switch, and the term typically refers to the switching device found in the Distributor of the An ignition system is a system for igniting a fuel-air mixture Similarly, in smaller scale circuits, the spark may not be enough to damage the switch but will still radiate undesirable radio frequency interference (RFI), which a filter capacitor absorbs. A spark-gap transmitter is a device for generating Radio frequency electromagnetic waves. Snubber capacitors are usually employed with a low-value resistor in series, to dissipate energy and minimize RFI. Such resistor-capacitor combinations are available in a single package.

In single phase squirrel cage motors, the primary winding within the motor housing isn't capable of starting a rotational motion on the rotor, but is capable of sustaining one. A squirrel cage rotor is the rotating part often used in an AC Induction motor. To start the motor, a secondary winding is used in series with a non-polarized starting capacitor to introduce a lag in the sinusoidal current through the secondary winding. When the secondary winding is placed at an angle with respect to the primary winding, a rotating electric field is created. The force of the rotational field is not constant, but is sufficient to start the rotor spinning. The capacitor is typically mounted to the side of the motor housing.

Capacitors are also used in parallel to interrupt units of a high-voltage circuit breaker in order to equally distribute the voltage between these units. A circuit breaker is an automatically-operated electrical Switch designed to protect an electrical circuit from damage caused by overload or In this case they are called grading 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). An electrolytic capacitor is a type of Capacitor that uses an ionic conducting liquid as one of its plates

Signal processing

The energy stored in a capacitor can be used to represent information, either in binary form, as in DRAMs, or in analogue form, as in analog sampled filters and CCDs. Information as a concept has a diversity of meanings from everyday usage to technical settings An analog sampled filter an Electronic filter that is a hybrid between an analog and a Digital filter. A charge-coupled device ( CCD) is an analog Shift register, that enables the transportation of analog signals (electric charges through successive stages (capacitors Capacitors can be used in analog circuits as components of integrators or more complex filters and in negative feedback loop stabilization. Analogue electronics (or analog in American English) are those electronic systems with a continuously Variable signal Negative Feedback feeds part of a System 's output inverted into the system's input generally with the result that fluctuations are attenuated Signal processing circuits also use capacitors to integrate a current signal. The European Space Agency 's INTErnational Gamma-Ray Astrophysics Laboratory ( INTEGRAL) is detecting some of the most energetic radiation that comes from space

Tuned circuits

Capacitors and inductors are applied together in tuned circuits to select information in particular frequency bands. An inductor is a passive electrical component designed to provide Inductance in a circuit An RLC circuit (also known as a Resonant circuit tuned circuit or LCR circuit is an Electrical circuit consisting of a Resistor (R an 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. Audio crossovers are a class of Electronic filters designed specifically for use in audio applications especially Hi-fi.

In a tuned circuit such as a radio receiver, the frequency selected is a function of the inductance (L) and the capacitance (C) in series, and is given by:

This is the frequency at which resonance occurs in an LC circuit. An LC circuit is a variety of resonant circuit or tuned circuit and consists of an Inductor, represented by the letter L and a Capacitor, represented This article is about a radio receiver for other uses see Radio (disambiguation. Frequency is a measure of the number of occurrences of a repeating event per unit Time. In Physics, resonance is the tendency of a system to Oscillate at maximum Amplitude at certain frequencies, known as the system's An LC circuit is a variety of resonant circuit or tuned circuit and consists of an Inductor, represented by the letter L and a Capacitor, represented

Other applications

Sensing

Most capacitors are designed to maintain a fixed physical structure. However, various factors can change the structure of the capacitor; the resulting change in capacitance can be used to sense those factors. A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument

Changing the dielectric: The effects of varying the physical and/or electrical characteristics of the dielectric can also be of use. Capacitors with an exposed and porous dielectric can be used to measure humidity in air.

Changing the distance between the plates: Capacitors are used to accurately measure the fuel level in airplanes. Overview Fixed-wing aircraft range from small training and recreational aircraft to Wide-body aircraft and military cargo aircraft. Capacitors with a flexible plate can be used to measure strain or pressure. Capacitors are used as the sensor in condenser microphones, where one plate is moved by air pressure, relative to the fixed position of the other plate. A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument Some accelerometers use MEMS capacitors etched on a chip to measure the magnitude and direction of the acceleration vector. An accelerometer is a device for measuring Acceleration and gravity induced reaction forces Microelectromechanical systems ( MEMS) is the technology of the very small and merges at the nano-scale into Nanoelectromechanical systems (NEMS and Nanotechnology They are used to detect changes in acceleration, eg. as tilt sensors or to detect free fall, as sensors triggering airbag deployment, and in many other applications. An airbag is part of a vehicle's safety restraint system a flexible envelope designed for rapid inflation in an automobile Collision, to prevent vehicle occupants Some fingerprint sensors use capacitors. Fingerprint recognition or fingerprint authentication refers to the Automated method of verifying a match between two human Fingerprints Fingerprints are Additionally, a user can adjust the pitch of a theremin musical instrument by moving his hand since this changes the effective capacitance between the user's hand and the antenna.

Changing the effective area of the plates: capacitive touch switches [1] [2] [3].

Pulsed power and weapons

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. In Electrical circuits, any Electric current i produces a Magnetic field and hence generates a total Magnetic flux \Phi acting Pulsed power is the term used to describe the science and technology of accumulating Energy over a relatively long period of time and releasing it very quickly thus increasing These include electromagnetic forming, Marx generators, pulsed lasers (especially TEA lasers), pulse forming networks, radar, fusion research, and particle accelerators. Electromagnetic forming ( EM forming or Magneforming) is a type of high energy rate metal forming process that uses Pulsed power techniques A Marx generator is a type of Electrical circuit first described by Erwin Otto Marx in 1924 whose purpose is to generate a high- Voltage pulse A laser is a device that emits Light ( Electromagnetic radiation) through a process called Stimulated emission. The CO2 TEA Laser was invented in the late 1960s by Dr Jacques Beaulieu working at the Defence Research Establishment Valcartier in Quebec, Canada A Pulse Forming Network (PFN accumulates Electrical energy over a comparatively long time then releases the stored energy in the form of a relatively square pulse Radar is a system that uses electromagnetic waves to identify the range altitude direction or speed of both moving and fixed objects such as Aircraft, ships The Z machine is the largest X-ray generator in the world and is designed to test materials in conditions of extreme temperature and pressure

Large capacitor banks(Reservoir) are used as energy sources for the exploding-bridgewire detonators or slapper detonators in nuclear weapons and other specialty weapons. The exploding-bridgewire detonator ( EBW, also known as exploding wire detonator) was invented by Luis Alvarez and Lawrence Johnson for the A slapper detonator is a relatively recent kind of a Detonator developed in Lawrence Livermore National Laboratory. A nuclear weapon is an explosive device that derives its destructive force from Nuclear reactions either fission or a combination of fission and fusion. Experimental work is under way using banks of capacitors as power sources for electromagnetic armour and electromagnetic railguns or coilguns. Electromagnetism is the Physics of the Electromagnetic field: a field which exerts a Force on particles that possess the property of For body armour see Armour, for armoured forces see Armoured warfare, for other uses see Armour (disambiguation. A railgun is a purely electrical Gun that accelerates a conductive projectile along a pair of metal rails using the same principles as the Homopolar motor. A coilgun is a type of synchronous Linear electric motor which is used as a Projectile accelerator that consists of one or more electromagnetic coils

See also Explosively pumped flux compression generator. An explosively pumped flux compression generator (EPFCG is a device used to generate a high-power Electromagnetic pulse by compressing magnetic flux using High explosive

Hazards and safety

Capacitors may retain a charge long after power is removed from a circuit; this charge can cause shocks (sometimes fatal) or damage to 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. A AA battery (double a or /ˈdʌbəl eɪ/ is a dry cell-type battery commonly used in portable Electronic devices This is easily capable of delivering an extremely painful shock.

Care must be taken to ensure that any large or high-voltage capacitor is properly discharged before servicing the containing equipment. For board-level capacitors, this is done by placing a bleeder resistor across the terminals, whose resistance is large enough that the leakage current will not affect the circuit, but small enough to discharge the capacitor shortly after power is removed. A bleeder resistor is a Resistor placed in parallel with a high-voltage supply for the purposes of discharging the energy stored in the power source's Filter High-voltage capacitors should be stored with the terminals shorted, since temporarily discharged capacitors can develop potentially dangerous voltages when the terminals are left open-circuited. Short Circuit is a 1986 comedy Science fiction film starring Ally Sheedy and Steve Guttenberg and directed by

Large oil-filled old capacitors must be disposed of properly as some contain polychlorinated biphenyls (PCBs). Polychlorinated biphenyls ( PCB s are a class of Organic compounds with 1 to 10 Chlorine atoms attached to Biphenyl which is a molecule composed It is known that waste PCBs can leak into groundwater under landfills. Groundwater is Water located beneath the Ground surface in Soil pore spaces and in the Fractures of lithologic formations For other uses see Water treatment and Land reclamation. A landfill, also known as a dump (and historically as If consumed by drinking contaminated water, PCBs are carcinogenic, even in very tiny amounts. The term carcinogen refers to any substance Radionuclide or radiation that is an agent directly involved in the promotion of Cancer or in the fatation of its propagation If the capacitor is physically large it is more likely to be dangerous and may require precautions in addition to those described above. New electrical components are no longer produced with PCBs. ("PCB" in electronics usually means printed circuit board, but the above usage is an exception. A printed circuit board, or PCB, is used to mechanically support and electrically connect Electronic components using conductive pathways or traces ) Capacitors containing PCB were labelled as containing "Askarel" and several other trade names.

High voltage

Above and beyond usual hazards associated with working with high-voltage high-energy circuits, there are a number of dangers that are specific to high-voltage capacitors. High-voltage capacitors may catastrophically fail when subjected to voltages or currents beyond their rating, or as they reach their normal end of life. Dielectric or metal interconnection failures may create arcing called an arc fault; within oil-filled units, that vaporizes dielectric fluid, resulting in case bulging, rupture, or even an explosion, called flash meltdown, that disperses flammable oil, starts fires, and damages nearby equipment. An explosion is a sudden increase in Volume and release of Energy in an extreme manner usually with the generation of high Temperatures and the release Rigid cased cylindrical glass or plastic cases are more prone to explosive rupture than rectangular cases due to an inability to easily expand under pressure. Capacitors used in RF or sustained high-current applications can overheat, especially in the center of the capacitor rolls. The trapped heat may cause rapid interior heating and destruction, even though the outer case remains relatively cool. Capacitors used within high-energy capacitor banks can violently explode when a fault in one capacitor causes sudden dumping of energy stored in the rest of the bank into the failing unit. High voltage vacuum capacitors can generate soft X-rays even during normal operation. Proper containment, fusing, and preventative maintenance can help to minimize these hazards.

High-voltage capacitors can benefit from a pre-charge to limit in-rush currents at power-up of HVDC circuits. Pre-charge of the powerline voltages in a high voltage DC application is a preliminary mode which current-limits the power source such that a controlled rise time of the system voltage This will extend the life of the component and may mitigate high-voltage hazards.

See also

Notes

References

• Zorpette, Glen (2005). "Super Charged: A Tiny South Korean Company is Out to Make Capacitors Powerful enough to Propel the Next Generation of Hybrid-Electric Cars". IEEE Spectrum 42 (1). IEEE Spectrum is a Magazine edited by the Institute of Electrical and Electronics Engineers. ISSN 0018-9235. An International Standard Serial Number ( ISSN) is a unique eight-digit number used to identify a print or electronic Periodical publication.  
• (1991) The ARRL Handbook for Radio Amateurs, 68th ed, Newington CT USA: The Amateur Radio Relay League.  
• Huelsman, Lawrence P. (1972). Basic Circuit Theory with Digital Computations, Series in computer applications in electrical engineering. Englewood Cliffs: Prentice-Hall. ISBN 0-13-057430-9.  
• Philosophical Transactions of the Royal Society LXXII, Appendix 8, 1782 (Volta coins the word condenser)
• A. K. Maini "Electronic Projects for Beginners", "Pustak Mahal", 2nd Edition: March, 1998 (INDIA)
• Spark Museum (von Kleist and Musschenbroek)
• Biography of von Kleist

External links

• The Capacitor Tutorial
• Capacitance and Inductance - a chapter from an online textbook
• Howstuffworks.com: How Capacitors Work
• CapSite 2007: Introduction to Capacitors
• AC circuits
• Capacitor Tutorial - Includes how to read capacitor temperature codes
• Capacitors in Circuits by Ernest Lee, The Wolfram Demonstrations Project. India, officially the Republic of India (भारत गणराज्य inc-Latn Bhārat Gaṇarājya; see also other Indian languages) is a country
• Instructables: DIY Make a Toy Capacitor
• Capacitor Converters and Calculators

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