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An inductor is a passive electrical device employed in electrical circuits for its property of inductance. An inductor can take many forms. Image File history File links Question_book-3. ... A passive component is an electronic component that does not require a source of energy to perform its intended function. ... A simple electric circuit made up of a voltage source and a resistor. ... An electric current i flowing around a circuit produces a magnetic field and hence a magnetic flux Φ through the circuit. ...

Common inductors.

Symbol used to denote an inductor

Image File history File linksMetadata Download high-resolution version (1170x1038, 154 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Inductor Metadata This file contains additional information, probably added from the digital camera or scanner used to create... Image File history File linksMetadata Download high-resolution version (1170x1038, 154 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Inductor Metadata This file contains additional information, probably added from the digital camera or scanner used to create... Image File history File links Inductor. ... Image File history File links Inductor. ...

Physics

Overview

Inductance (L, measured in Henrys) is an effect which results from the magnetic field that forms around a current-carrying conductor. Electric current through the conductor creates a magnetic flux proportional to the current. A change in this current creates a change in magnetic flux that, in turn, generates an electromotive force (EMF) that acts to oppose this change in current. Inductance is a measure of the amount of EMF generated for a unit change in current. For example, an inductor with an inductance of 1 henry produces an EMF of 1 volt when the current through the inductor changes at the rate of 1 ampere per second. The number of loops, the size of each loop, and the material it is wrapped around all affect the inductance. For example, the magnetic flux linking these turns can be increased by coiling the conductor around a material with a high permeability. An electric current i flowing around a circuit produces a magnetic field and hence a magnetic flux Φ through the circuit. ... The henry (symbol H) is the SI unit of inductance. ... For the indie-pop band, see The Magnetic Fields. ... In science and engineering, conductors, such as copper or aluminum, are materials with atoms having loosely held valence electrons. ... This box:      Electric current is the flow (movement) of electric charge. ... Magnetic flux, represented by the Greek letter Φ (phi), is a measure of quantity of magnetism, taking account of the strength and the extent of a magnetic field. ... Electromotive force (emf) is the amount of energy gained per unit charge that passes through a device in the opposite direction to the electric field existing across that device. ... In electromagnetism, permeability is the degree of magnetization of a material that responds linearly to an applied magnetic field. ...

Stored energy

The energy (measured in joules, in SI) stored by an inductor is equal to the amount of work required to establish the current through the inductor, and therefore the magnetic field. This is given by: The joule (IPA: or ) (symbol: J) is the SI unit of energy. ... Look up si, Si, SI in Wiktionary, the free dictionary. ...

where L is inductance and I is the current through the inductor.

Hydraulic model

Electric current can be modeled by the hydraulic analogy. The inductor can be modeled by the flywheel effect of a turbine rotated by the flow. As can be demonstrated intuitively and mathematically, this mimics the behavior of an electrical inductor; voltage is proportional to the derivative of current with respect to time. Thus a rapid change in current will cause a big voltage spike. Likewise, in cases of a sudden interruption of water flow the turbine will generate a high pressure across the blockage, etc. Magnetic interactions such as in transformers are not modeled hydraulically. Since electric current is invisible and the processes at play in electronics are often difficult to understand in an intuitive way, it is common to teach electronics using analogies to more common sense objects and processes. ... Spoked flywheel Flywheel from stationary engine. ... A Siemens steam turbine with the case opened. ... For other uses, see Transformer (disambiguation). ...

Applications

A choke with two 47mH windings, such as might be found in a power supply.

Inductors are used extensively in analog circuits and signal processing. Inductors in conjunction with capacitors and other components form tuned circuits which can emphasize or filter out specific signal frequencies. This can range from the use of large inductors as chokes in power supplies, which in conjunction with filter capacitors remove residual hum or other fluctuations from the direct current output, to such small inductances as generated by a ferrite bead or torus around a cable to prevent radio frequency interference from being transmitted down the wire. Smaller inductor/capacitor combinations provide tuned circuits used in radio reception and broadcasting, for instance. Image File history File links Metadata Size of this preview: 473 × 599 pixelsFull resolution (856 × 1084 pixel, file size: 239 KB, MIME type: image/jpeg) Other versions None. ... Image File history File links Metadata Size of this preview: 473 × 599 pixelsFull resolution (856 × 1084 pixel, file size: 239 KB, MIME type: image/jpeg) Other versions None. ... A Choke is an inductor designed to have a high reactance to a particular frequency when used in a signal-carrying circuit. ... It has been suggested that this article or section be merged with Analog electronics. ... See Capacitor (component) for a discussion of specific types. ... Television signal splitter consisting of a hi-pass filter (left) and a low-pass filter (right). ... See Capacitor (component) for a discussion of specific types. ... A hum is a sound with a particular timbre (or sound quality), usually a monotone or with slightly varying tones, often produced by machinery in operation or by insects in flight. ... A stack of ferrite magnets Ferrites are electrically non-conductive ferrimagnetic ceramic compound materials, consisting of various mixtures of iron oxides such as Hematite (Fe2O3) or Magnetite (Fe3O4) and the oxides of other metals. ... In geometry, a torus (pl. ... Radio Frequency Interference (RFI) is electromagnetic radiation which is emitted by electrical circuits carrying rapidly changing signals, as a by-product of their normal operation, and which causes unwanted signals (interference or noise) to be induced in other circuits. ... An RLC circuit (sometimes known as resonant or tuned circuit) is an electrical circuit comprising a resistor (R), an inductor (L), and a capacitor (C), connected in series or in parallel. ...

Two (or more) inductors which have coupled magnetic flux form a transformer, which is a fundamental component of every electric utility power grid. The efficiency of a transformer decreases as the frequency increases but size can be decreased as well; for this reason, aircraft use 400 hertz alternating current rather than the usual 50 or 60 hertz, allowing a great saving in weight from the use of smaller transformers. For other uses, see Transformer (disambiguation). ... A public utility is a company that maintains the infrastructure for a public service. ...

An inductor is used as the energy storage device in some switchmode power supplies. The inductor is energized for a specific fraction of the regulator's switching frequency, and de-energized for the remainder of the cycle. This energy transfer ratio determines the input-voltage to output-voltage ratio. This X_L is used in complement with an active semiconductor device to maintain very accurate voltage control. A switching-mode power supply for laboratory use. ...

Inductors are also employed in electrical transmission systems, where they are used to intentionally depress system voltages or limit fault current. In this field, they are more commonly referred to as reactors. A term generally used to indicate an abnormal flow of current in an electric circuit due to a fault (usually a short circuit or abnormally low impedance path). ...

As inductors tend to be larger and heavier than other components, their use has been reduced in modern equipment; solid state switching power supplies eliminate large transformers, for instance, and circuits are designed to use only small inductors, if any; larger values are simulated by use of gyrator circuits. The gyrator is an electric circuit which inverts an impedance. ...

Inductor construction

Inductors. Major scale in centimetres.

An inductor is usually constructed as a coil of conducting material, typically copper wire, wrapped around a core either of air or of ferromagnetic material. Core materials with a higher permeability than air confine the magnetic field closely to the inductor, thereby increasing the inductance. Inductors come in many shapes. Most are constructed as enamel coated wire wrapped around a ferrite bobbin with wire exposed on the outside, while some enclose the wire completely in ferrite and are called "shielded". Some inductors have an adjustable core, which enables changing of the inductance. Inductors used to block very high frequencies are sometimes made with a wire passing through a ferrite cylinder or bead. Image File history File linksMetadata Download high resolution version (684x854, 91 KB) Some inductors. ... Image File history File linksMetadata Download high resolution version (684x854, 91 KB) Some inductors. ... A centimetre (American spelling centimeter, symbol cm) is a unit of length that is equal to one hundredth of a metre, the current SI base unit of length. ... A coil is a series of loops. ... In science and engineering, conductors, such as copper or aluminum, are materials with atoms having loosely held valence electrons. ... A magnetic core is the core of an electromagnet or inductor. ... Ferromagnetism is a phenomenon by which a material can exhibit a spontaneous magnetization, and is one of the strongest forms of magnetism. ... In electromagnetism, permeability is the degree of magnetization of a material that responds linearly to an applied magnetic field. ... A stack of ferrite magnets Ferrites are electrically non-conductive ferrimagnetic ceramic compound materials, consisting of various mixtures of iron oxides such as Hematite (Fe2O3) or Magnetite (Fe3O4) and the oxides of other metals. ... A bobbin is a spindle or cylinder, with or without flanges, on which wire, yarn, thread or film is wound. ...

Small inductors can be etched directly onto a printed circuit board by laying out the trace in a spiral pattern. Small value inductors can also be built on integrated circuits using the same processes that are used to make transistors. In these cases, aluminium interconnect is typically used as the conducting material. However, practical constraints make it far more common to use a circuit called a "gyrator" which uses a capacitor and active components to behave similarly to an inductor. Part of a 1983 Sinclair ZX Spectrum computer board. ... This article does not cite any references or sources. ... Integrated circuit of Atmel Diopsis 740 System on Chip showing memory blocks, logic and input/output pads around the periphery Microchips with a transparent window, showing the integrated circuit inside. ... Assorted discrete transistors A transistor is a semiconductor device, commonly used as an amplifier or an electrically controlled switch. ... The term connection (also rendered connexion - this alternative spelling is now generally considered old-fashioned, but it was the house style of The Times of London until at least the late 1970s) has various uses, including: An act of connecting two or more physical entities in a physical sense or... The gyrator is an electric circuit which inverts an impedance. ... See Capacitor (component) for a discussion of specific types. ...

In electric circuits

While a capacitor opposes changes in voltage, an inductor opposes changes in current. An ideal inductor would offer no resistance to a constant direct current; however, only superconducting inductors have truly zero electrical resistance. See Capacitor (component) for a discussion of specific types. ... Direct current (DC or continuous current) is the continuous flow of electricity through a conductor such as a wire from high to low potential. ... Superconductivity is a phenomenon occurring in certain materials at low temperatures, characterised by the complete absence of electrical resistance and the damping of the interior magnetic field (the Meissner effect. ... Electrical resistance is a measure of the degree to which an electrical component opposes the passage of current. ...

In general, the relationship between the time-varying voltage v(t) across an inductor with inductance L and the time-varying current i(t) passing through it is described by the differential equation: Visualization of airflow into a duct modelled using the Navier-Stokes equations, a set of partial differential equations. ...

When there is a sinusoidal alternating current (AC) through an inductor, a sinusoidal voltage is induced. The amplitude of the voltage is proportional to the product of the amplitude (I_P) of the current and the frequency ( f ) of the current. In mathematics, the trigonometric functions are functions of an angle, important when studying triangles and modeling periodic phenomena. ... City lights viewed in a motion blurred exposure. ...

In this situation, the phase of the current lags that of the voltage by 90 degrees. This article is about a portion of a periodic process. ...

Laplace circuit analysis (s-domain)

When using the Laplace transform in circuit analysis, the transfer impedance of an ideal inductor with no initial current is represented in the s domain by: In the branch of mathematics called functional analysis, the Laplace transform, , is a linear operator on a function f(t) (original ) with a real argument t (t ≥ 0) that transforms it to a function F(s) (image) with a complex argument s. ...

where

L is the inductance, and

s is the complex frequency

If the inductor does have initial current, it can be represented by:

• adding a voltage source in series with the inductor, having the value:

(Note that the source should have a polarity that opposes the initial current)

• or by adding a current source in parallel with the inductor, having the value:

where

L is the inductance, and

I₀ is the initial current in the inductor.

Inductor networks

Main article: Series and parallel circuits

Inductors in a parallel configuration each have the same potential difference (voltage). To find their total equivalent inductance (L_eq): Electrical circuit components can be connected together in one of two ways: series or parallel. ... Electrical circuit components can be connected together in one of two ways: series or parallel. ...

The current through inductors in series stays the same, but the voltage across each inductor can be different. The sum of the potential differences (voltage) is equal to the total voltage. To find their total inductance: Image File history File links Inductors_in_parallel. ... Electrical circuit components can be connected together in one of two ways: series or parallel. ...

These simple relationships hold true only when there is no mutual coupling of magnetic fields between individual inductors. Image File history File links Inductors_in_series. ...

Q factor

An ideal inductor will be lossless irrespective of the amount of current through the winding. However, typically inductors have winding resistance from the metal wire forming the coils. Since the winding resistance appears as a resistance in series with the inductor, it is often called the series resistance. The inductor's series resistance converts electrical current through the coils into heat, thus causing a loss of inductive quality. The quality factor (or Q) of an inductor is the ratio of its inductive reactance to its resistance at a given frequency, and is a measure of its efficiency. The higher the Q factor of the inductor, the closer it approaches the behavior of an ideal, lossless, inductor. This article or section does not cite any references or sources. ...

The Q factor of an inductor can be found through the following formula, where R is its internal electrical resistance: Electrical resistance is a measure of the degree to which an electrical component opposes the passage of current. ...

By using a ferromagnetic core the inductance is increased for the same amount of copper, raising the Q. Cores however also introduce losses that increase with frequency. A grade of core material is chosen for best results for the frequency band. At VHF or higher frequencies an air core is likely to be used. Inductors wound around a ferromagnetic core may saturate at high currents, causing a dramatic decrease in inductance (and Q). This phenomenon can be avoided by using a (physically larger) air core inductor. A well designed air core inductor may have a Q of several hundred. Ferromagnetism is a phenomenon by which a material can exhibit a spontaneous magnetization, and is one of the strongest forms of magnetism. ... Very high frequency (VHF) is the radio frequency range from 30 MHz to 300 MHz. ... For magnetic materials, saturation is the state when the material can not absorb a stronger magnetic field, such that an increase of magnetization produces no significant change in magnetic flux density. ...

An almost ideal inductor (Q approaching infinity) can be created by immersing a coil made from a superconducting alloy in liquid helium or liquid nitrogen. This supercools the wire, causing its winding resistance to disappear. Because a superconducting inductor is virtually lossless, it can store a large amount of electrical energy within the surrounding magnetic field (see superconducting magnetic energy storage). Superconductivity is a phenomenon occurring in certain materials at low temperatures, characterised by the complete absence of electrical resistance and the damping of the interior magnetic field (the Meissner effect. ... An alloy is a homogeneous hybrid of two or more elements, at least one of which is a metal, and where the resulting material has metallic properties. ... Helium exists in liquid form only at very low temperatures. ... A tank of liquid nitrogen, used to supply a cryogenic freezer (for storing laboratory samples at a temperature of about -150 Celsius). ... the flow of direct current in a superconducting coil which has been cryogenically cooled to a temperature below its superconducting critical temperature. ...

Formulae

The table below lists some common formulae for calculating the theoretical inductance of several inductor constructions.

Construction	Formula	Dimensions
Cylindrical coil		L = inductance in henries (H) μ0 = permeability of free space = 4π × 10-7 H/m μr = relative permeability of core material N = number of turns A = area of cross-section of the coil in square metres (m2) l = length of coil in metres (m)
Straight wire conductor		L = inductance (H) l = length of conductor (m) d = diameter of conductor (m)
		L = inductance (nH) l = length of conductor (in) d = diameter of conductor (in)
Short air-core cylindrical coil		L = inductance (µH) r = outer radius of coil (in) l = length of coil (in) N = number of turns
Multilayer air-core coil		L = inductance (µH) r = mean radius of coil (in) l = physical length of coil winding (in) N = number of turns d = depth of coil (outer radius minus inner radius) (in)
Flat spiral air-core coil		L = inductance (H) r = mean radius of coil (m) N = number of turns d = depth of coil (outer radius minus inner radius) (m)
		L = inductance (µH) r = mean radius of coil (in) N = number of turns d = depth of coil (outer radius minus inner radius) (in)
Toroidal core (circular cross-section)		L = inductance (H) μ0 = permeability of free space = 4π × 10-7 H/m μr = relative permeability of core material N = number of turns r = radius of coil winding (m) D = overall diameter of toroid (m)

The henry (symbol H) is the SI unit of inductance. ... This article is in need of attention. ... In electromagnetism, permeability is the degree of magnetization of a material that responds linearly to an applied magnetic field. ... A square metre (US spelling: square meter) is by definition the area enclosed by a square with sides each 1 metre long. ... This article is about the unit of length. ... In electromagnetism, permeability is the degree of magnetization of a material that responds linearly to an applied magnetic field. ... Look up Vacuum in Wiktionary, the free dictionary. ...

See also

Various components An electronic component is a basic electronic element usually packaged in a discrete form with two or more connecting leads or metallic pads. ... See Capacitor (component) for a discussion of specific types. ... Resistor symbols (American) Resistor symbols (Europe, IEC) Axial-lead resistors on tape. ... Electricity (from New Latin ēlectricus, amberlike) is a general term for a variety of phenomena resulting from the presence and flow of electric charge. ... This article is about the engineering discipline. ... The gyrator is an electric circuit which inverts an impedance. ... An electric current i flowing around a circuit produces a magnetic field and hence a magnetic flux Φ through the circuit. ... An induction coil or spark coil (archaically known as a Ruhmkorff coil) is a type of disruptive discharge coil. ... Induction Hob (Top View) An induction cooker uses induction heating for cooking. ... This article needs to be wikified. ... A magnetic core is the core of an electromagnet or inductor. ... A saturable reactor was a special form of inductor where the magnetic core could be deliberately saturated by means of a dc current flowing in a control winding. ... For other uses, see Transformer (disambiguation). ... It has been suggested that Electric reactance be merged into this article or section. ... This article does not cite any references or sources. ... An RLC circuit (also known as a resonant circuit or a tuned circuit) is an electrical circuit consisting of a resistor (R), an inductor (L), and a capacitor (C), connected in series or in parallel. ...

Synonyms

• coil
• Choke (electronics)
• reactor

A coil is a series of loops. ... A Choke is an inductor designed to have a high reactance to a particular frequency when used in a signal-carrying circuit. ... Reactor may relate to the folowing: A chemical reactor: a device for containing and controlling a chemical reaction. ...

External links

General

• How stuff works The initial concept, made very simple
• Capacitance and Inductance - A chapter from an online textbook
• Spiral inductor models. Good article on inductor characteristics and modeling.
• Online coil inductance calculator. Online calculator calculates the inductance of conventional and toroidal coils using formulas 3, 4, 5, and 6, above.
• AC circuits
• [1]- Understanding coils and transforms
• [2] - Circuit Schematic Symbols