Diode

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Diode

Figure 1: Closeup of a diode, showing the squareshaped semiconductor crystal (black object on left).

Figure 2: Various semiconductor diodes.Bottom: A bridge rectifier. In most diodes,a white or black painted band identifies thecathode terminal, that is, the terminal that

positive charge (conventional current)would flow out of when the diode is

conducting.[1][2][3][4]

In electronics, a diode is a two-terminal electronic componentwith an asymmetric transfer characteristic, with low (ideally zero)resistance to current flow in one direction, and high (ideallyinfinite) resistance in the other. A semiconductor diode, the mostcommon type today, is a crystalline piece of semiconductormaterial with a p-n junction connected to two electricalterminals.[5] A vacuum tube diode is a vacuum tube with twoelectrodes, a plate (anode) and heated cathode.

The most common function of a diode is to allow an electriccurrent to pass in one direction (called the diode's forwarddirection), while blocking current in the opposite direction (thereverse direction). Thus, the diode can be viewed as an electronicversion of a check valve. This unidirectional behavior is calledrectification, and is used to convert alternating current to directcurrent, including extraction of modulation from radio signals inradio receivers—these diodes are forms of rectifiers.

However, diodes can have more complicated behavior than thissimple on–off action. Semiconductor diodes begin conductingelectricity only if a certain threshold voltage or cut-in voltage ispresent in the forward direction (a state in which the diode is saidto be forward-biased). The voltage drop across a forward-biaseddiode varies only a little with the current, and is a function oftemperature; this effect can be used as a temperature sensor orvoltage reference.

Semiconductor diodes' nonlinear current–voltage characteristiccan be tailored by varying the semiconductor materials anddoping, introducing impurities into the materials. These areexploited in special-purpose diodes that perform many differentfunctions. For example, diodes are used to regulate voltage (Zenerdiodes), to protect circuits from high voltage surges (avalanchediodes), to electronically tune radio and TV receivers (varactordiodes), to generate radio frequency oscillations (tunnel diodes,Gunn diodes, IMPATT diodes), and to produce light (lightemitting diodes). Tunnel diodes exhibit negative resistance, whichmakes them useful in some types of circuits.

Diodes were the first semiconductor electronic devices. Thediscovery of crystals' rectifying abilities was made by Germanphysicist Ferdinand Braun in 1874. The first semiconductordiodes, called cat's whisker diodes, developed around 1906, weremade of mineral crystals such as galena. Today most diodes aremade of silicon, but other semiconductors such as germanium are sometimes used.[6]

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Figure 3: Structure of a vacuum tube diode. Thefilament may be bare, or more commonly (as shown

here), embedded within and insulated from anenclosing cathode

History

Although the crystal semiconductor diode was popular before thethermionic diode, thermionic (vacuum tube) diodes and solid state(semiconductor) diodes were developed in parallel. Until the1950's vacuum tube diodes were more often used in radios becausesemiconductor alternatives (Cat's Whiskers) were less stable, andbecause most receiving sets would have vacuum tubes foramplification that could easily have diodes included in the tube(for example the 12SQ7 double-diode triode), and vacuum tuberectifiers and gas-filled rectifiers handled some high voltage/highcurrent rectification tasks beyond the capabilities of semiconductordiodes (such as selenium rectifiers) available at the time.

Discovery of vacuum tube diodes

In 1873, Frederick Guthrie discovered the basic principle ofoperation of thermionic diodes.[7] Guthrie discovered that apositively charged electroscope could be discharged by bringing agrounded piece of white-hot metal close to it (but not actuallytouching it). The same did not apply to a negatively chargedelectroscope, indicating that the current flow was only possible inone direction.

Thomas Edison independently rediscovered the principle on February 13, 1880. At the time, Edison wasinvestigating why the filaments of his carbon-filament light bulbs nearly always burned out at the positive-connectedend. He had a special bulb made with a metal plate sealed into the glass envelope. Using this device, he confirmedthat an invisible current flowed from the glowing filament through the vacuum to the metal plate, but only when theplate was connected to the positive supply.

Edison devised a circuit where his modified light bulb effectively replaced the resistor in a DC voltmeter. Edisonwas awarded a patent for this invention in 1884.[8] Since there was no apparent practical use for such a device at thetime, the patent application was most likely simply a precaution in case someone else did find a use for the so-calledEdison effect.

About 20 years later, John Ambrose Fleming (scientific adviser to the Marconi Company and former Edisonemployee) realized that the Edison effect could be used as a precision radio detector. Fleming patented the first truethermionic diode, the Fleming valve, in Britain on November 16, 1904[9] (followed by U.S. Patent 803,684 [10] inNovember 1905).

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Solid-state diodesIn 1874 German scientist Karl Ferdinand Braun discovered the "unilateral conduction" of crystals.[11] Braun patentedthe crystal rectifier in 1899.[12] Copper oxide and selenium rectifiers were developed for power applications in the1930s.Indian scientist Jagadish Chandra Bose was the first to use a crystal for detecting radio waves in 1894.[13][14] Thecrystal detector was developed into a practical device for wireless telegraphy by Greenleaf Whittier Pickard, whoinvented a silicon crystal detector in 1903 and received a patent for it on November 20, 1906.[15] Otherexperimenters tried a variety of other substances, of which the most widely used was the mineral galena (leadsulfide). Other substances offered slightly better performance, but galena was most widely used because it had theadvantage of being cheap and easy to obtain. The crystal detector in these early crystal radio sets consisted of anadjustable wire point-contact (the so-called "cat's whisker"), which could be manually moved over the face of thecrystal in order to obtain optimum signal. This troublesome device was superseded by thermionic diodes by the1920s, but after high purity semiconductor materials became available, the crystal detector returned to dominant usewith the advent of inexpensive fixed-germanium diodes in the 1950s.

EtymologyAt the time of their invention, such devices were known as rectifiers. In 1919, the year tetrodes were invented,William Henry Eccles coined the term diode from the Greek roots di (from δί), meaning "two", and ode (from ὁδός),meaning "path".

Rectifiers

Although all diodes rectify, the term rectifier is normally reserved for higher currents and voltages than wouldnormally found in the rectification of lower power signals; examples include:• power supply (half-wave or full-wave or bridge) rectifiers• CRT (especially TV) Extra-high voltage flyback, "damper" or "booster" diodes such as the 6AU4GTA.[16]

Thermionic diodes

Figure 4: The symbol for an indirectheated vacuum-tube diode. From top tobottom, the components are the anode,the cathode, and the heater filament.

Thermionic diodes are thermionic-valve devices (also known as vacuumtubes, tubes, or valves), which are arrangements of electrodes surrounded by avacuum within a glass envelope. Early examples were fairly similar inappearance to incandescent light bulbs.

In thermionic-valve diodes, a current through the heater filament indirectlyheats the thermionic cathode, another internal electrode treated with a mixtureof barium and strontium oxides, which are oxides of alkaline earth metals;these substances are chosen because they have a small work function. (Somevalves use direct heating, in which a tungsten filament acts as both heater andcathode.) The heat causes thermionic emission of electrons into the vacuum.In forward operation, a surrounding metal electrode called the anode ispositively charged so that it electrostatically attracts the emitted electrons.However, electrons are not easily released from the unheated anode surfacewhen the voltage polarity is reversed. Hence, any reverse flow is negligible.

In a mercury-arc valve, an arc forms between a refractory conductive anode and a pool of liquid mercury acting as cathode. Such units were made with ratings up to hundreds of kilowatts, and were important in the development of HVDC power transmission. Some types of smaller thermionic rectifiers sometimes had mercury vapor fill to reduce

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their forward voltage drop and to increase current rating over thermionic hard-vacuum devices.Until the development of semiconductor diodes, valve diodes were used in analog signal applications and asrectifiers in many power supplies. They rapidly ceased to be used for most purposes, an exception being somehigh-voltage high-current applications subject to large transient peaks, where their robustness to abuse made themthe best choice. As of 2012 some enthusiasts favoured vacuum tube amplifiers for audio applications, sometimesusing valve rather than semiconductor rectifiers.

Semiconductor diodes

Electronic symbolsThe symbol used for a semiconductor diode in a circuit diagram specifies the type of diode. There are alternatesymbols for some types of diodes, though the differences are minor.

Diode Light Emitting Diode (LED) Photodiode Schottky diode

TransientVoltage

Suppression(TVS)

Tunnel diode Varicap Zener diode

Figure 7: Typical diode packages in same alignment as diodesymbol. Thin bar depicts the cathode.

Point-contact diodes

A point-contact diode works the same as the junctiondiodes described below, but their construction issimpler. A block of n-type semiconductor is built, and aconducting sharp-point contact made with somegroup-3 metal is placed in contact with thesemiconductor. Some metal migrates into thesemiconductor to make a small region of p-typesemiconductor near the contact. The long-popular1N34 germanium version is still used in radio receiversas a detector and occasionally in specialized analog electronics.

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Junction diodesMost diodes today are silicon junction diodes. A junction is formed between the p and n regions which is also calleda depletion region.

p–n junction diode

A p–n junction diode is made of a crystal of semiconductor. Impurities are added to it to create a region on one sidethat contains negative charge carriers (electrons), called n-type semiconductor, and a region on the other side thatcontains positive charge carriers (holes), called p-type semiconductor. When two materials i.e. n-type and p-type areattached together, a momentary flow of electrons occur from n to p side resulting in a third region where no chargecarriers are present. It is called Depletion region due to the absence of charge carriers (electrons and holes in thiscase). The diode's terminals are attached to each of these regions. The boundary between these two regions, called ap–n junction, is where the action of the diode takes place. The crystal allows electrons to flow from the N-type side(called the cathode) to the P-type side (called the anode), but not in the opposite direction.

Schottky diode

Another type of junction diode, the Schottky diode, is formed from a metal–semiconductor junction rather than ap–n junction, which reduces capacitance and increases switching speed.

Current–voltage characteristicA semiconductor diode’s behavior in a circuit is given by its current–voltage characteristic, or I–V graph (see graphbelow). The shape of the curve is determined by the transport of charge carriers through the so-called depletion layeror depletion region that exists at the p–n junction between differing semiconductors. When a p–n junction is firstcreated, conduction-band (mobile) electrons from the N-doped region diffuse into the P-doped region where there isa large population of holes (vacant places for electrons) with which the electrons "recombine". When a mobileelectron recombines with a hole, both hole and electron vanish, leaving behind an immobile positively charged donor(dopant) on the N side and negatively charged acceptor (dopant) on the P side. The region around the p–n junctionbecomes depleted of charge carriers and thus behaves as an insulator.However, the width of the depletion region (called the depletion width) cannot grow without limit. For eachelectron–hole pair that recombines, a positively charged dopant ion is left behind in the N-doped region, and anegatively charged dopant ion is left behind in the P-doped region. As recombination proceeds more ions are created,an increasing electric field develops through the depletion zone that acts to slow and then finally stop recombination.At this point, there is a "built-in" potential across the depletion zone.If an external voltage is placed across the diode with the same polarity as the built-in potential, the depletion zonecontinues to act as an insulator, preventing any significant electric current flow (unless electron/hole pairs areactively being created in the junction by, for instance, light. see photodiode). This is the reverse bias phenomenon.However, if the polarity of the external voltage opposes the built-in potential, recombination can once again proceed,resulting in substantial electric current through the p–n junction (i.e. substantial numbers of electrons and holesrecombine at the junction). For silicon diodes, the built-in potential is approximately 0.7 V (0.3 V for Germaniumand 0.2 V for Schottky). Thus, if an external current is passed through the diode, about 0.7 V will be developedacross the diode such that the P-doped region is positive with respect to the N-doped region and the diode is said tobe "turned on" as it has a forward bias.A diode’s I–V characteristic can be approximated by four regions of operation.

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Figure 5: I–V characteristics of a p–n junctiondiode (not to scale—the current in the reverseregion is magnified compared to the forward

region, resulting in the apparent slopediscontinuity at the origin; the actual I–V curve is

smooth across the origin).

At very large reverse bias, beyond the peak inverse voltage or PIV, a process called reverse breakdown occurs thatcauses a large increase in current (i.e., a large number of electrons and holes are created at, and move away from thep–n junction) that usually damages the device permanently. The avalanche diode is deliberately designed for use inthe avalanche region. In the Zener diode, the concept of PIV is not applicable. A Zener diode contains a heavilydoped p–n junction allowing electrons to tunnel from the valence band of the p-type material to the conduction bandof the n-type material, such that the reverse voltage is "clamped" to a known value (called the Zener voltage), andavalanche does not occur. Both devices, however, do have a limit to the maximum current and power in the clampedreverse-voltage region. Also, following the end of forward conduction in any diode, there is reverse current for ashort time. The device does not attain its full blocking capability until the reverse current ceases.The second region, at reverse biases more positive than the PIV, has only a very small reverse saturation current. Inthe reverse bias region for a normal P–N rectifier diode, the current through the device is very low (in the µA range).However, this is temperature dependent, and at sufficiently high temperatures, a substantial amount of reversecurrent can be observed (mA or more).The third region is forward but small bias, where only a small forward current is conducted.As the potential difference is increased above an arbitrarily defined "cut-in voltage" or "on-voltage" or "diodeforward voltage drop (Vd)", the diode current becomes appreciable (the level of current considered "appreciable" andthe value of cut-in voltage depends on the application), and the diode presents a very low resistance. Thecurrent–voltage curve is exponential. In a normal silicon diode at rated currents, the arbitrary cut-in voltage isdefined as 0.6 to 0.7 volts. The value is different for other diode types—Schottky diodes can be rated as low as 0.2V, Germanium diodes 0.25 to 0.3 V, and red or blue light-emitting diodes (LEDs) can have values of 1.4 V and 4.0V respectively.[17]

At higher currents the forward voltage drop of the diode increases. A drop of 1 V to 1.5 V is typical at full ratedcurrent for power diodes.

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Shockley diode equationThe Shockley ideal diode equation or the diode law (named after transistor co-inventor William Bradford Shockley)gives the I–V characteristic of an ideal diode in either forward or reverse bias (or no bias). The equation is:

whereI is the diode current,IS is the reverse bias saturation current (or scale current),VD is the voltage across the diode,VT is the thermal voltage, andn is the ideality factor, also known as the quality factor or sometimes emission coefficient. The ideality factorn typically varies from 1 to 2 (though can in some cases be higher), depending on the fabrication process andsemiconductor material and in many cases is assumed to be approximately equal to 1 (thus the notation n isomitted).

The thermal voltage VT is approximately 25.85 mV at 300 K, a temperature close to "room temperature" commonlyused in device simulation software. At any temperature it is a known constant defined by:

where k is the Boltzmann constant, T is the absolute temperature of the p–n junction, and q is the magnitude ofcharge on an electron (the elementary charge).The reverse saturation current, IS, is not constant for a given device, but varies with temperature; usually moresignificantly than VT, so that VD typically decreases as T increases.The Shockley ideal diode equation or the diode law is derived with the assumption that the only processes giving riseto the current in the diode are drift (due to electrical field), diffusion, and thermal recombination–generation (R–G).It also assumes that the R–G current in the depletion region is insignificant. This means that the Shockley equationdoesn’t account for the processes involved in reverse breakdown and photon-assisted R–G. Additionally, it doesn’tdescribe the "leveling off" of the I–V curve at high forward bias due to internal resistance.Under reverse bias voltages (see Figure 5) the exponential in the diode equation is negligible, and the current is aconstant (negative) reverse current value of −IS. The reverse breakdown region is not modeled by the Shockley diodeequation.For even rather small forward bias voltages (see Figure 5) the exponential is very large because the thermal voltageis very small, so the subtracted ‘1’ in the diode equation is negligible and the forward diode current is oftenapproximated as

The use of the diode equation in circuit problems is illustrated in the article on diode modeling.

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Small-signal behaviorFor circuit design, a small-signal model of the diode behavior often proves useful. A specific example of diodemodeling is discussed in the article on small-signal circuits.

Reverse-recovery effectFollowing the end of forward conduction in a p–n type diode, a reverse current flows for a short time. The devicedoes not attain its blocking capability until the mobile charge in the junction is depleted.The effect can be significant when switching large currents very quickly.[18] A certain amount of "reverse recoverytime" tr (on the order of tens of nanoseconds to a few microseconds) may be required to remove the reverse recoverycharge Qr from the diode. During this recovery time, the diode can actually conduct in the reverse direction. Incertain real-world cases it can be important to consider the losses incurred by this non-ideal diode effect.[19]

However, when the slew rate of the current is not so severe (e.g. Line frequency) the effect can be safely ignored.For most applications, the effect is also negligible for Schottky diodes.The reverse current ceases abruptly when the stored charge is depleted; this abrupt stop is exploited in step recoverydiodes for generation of extremely short pulses.

Types of semiconductor diode

Figure 8: Several types of diodes. The scale iscentimeters.

There are several types of p–n junction diodes, which either emphasizea different physical aspect of a diode often by geometric scaling,doping level, choosing the right electrodes, are just an application of adiode in a special circuit, or are really different devices like the Gunnand laser diode and the MOSFET:

Normal (p–n) diodes, which operate as described above, are usuallymade of doped silicon or, more rarely, germanium. Before thedevelopment of silicon power rectifier diodes, cuprous oxide and laterselenium was used; its low efficiency gave it a much higher forwardvoltage drop (typically 1.4 to 1.7 V per "cell", with multiple cellsstacked to increase the peak inverse voltage rating in high voltagerectifiers), and required a large heat sink (often an extension of thediode’s metal substrate), much larger than a silicon diode of the samecurrent ratings would require. The vast majority of all diodes are thep–n diodes found in CMOS integrated circuits, which include twodiodes per pin and many other internal diodes.

Avalanche diodesDiodes that conduct in the reverse direction when the reverse bias voltage exceeds the breakdown voltage.These are electrically very similar to Zener diodes, and are often mistakenly called Zener diodes, but breakdown by a different mechanism, the avalanche effect. This occurs when the reverse electric field across thep–n junction causes a wave of ionization, reminiscent of an avalanche, leading to a large current. Avalanchediodes are designed to break down at a well-defined reverse voltage without being destroyed. The differencebetween

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Typical datasheet drawing showing thedimensions of a DO-41 diode package.

the avalanche diode (which has a reverse breakdown above about 6.2 V)and the Zener is that the channel length of the former exceeds the meanfree path of the electrons, so there are collisions between them on the wayout. The only practical difference is that the two types have temperaturecoefficients of opposite polarities.

Cat’s whisker or crystal diodesThese are a type of point-contact diode. The cat’s whisker diode consistsof a thin or sharpened metal wire pressed against a semiconductingcrystal, typically galena or a piece of coal. The wire forms the anode andthe crystal forms the cathode. Cat’s whisker diodes were also calledcrystal diodes and found application in crystal radio receivers. Cat’swhisker diodes are generally obsolete, but may be available from a fewmanufacturers.

Constant current diodes

These are actually a JFET[20] with the gate shorted to the source, and function like a two-terminalcurrent-limiter analog to the Zener diode, which is limiting voltage. They allow a current through them to riseto a certain value, and then level off at a specific value. Also called CLDs, constant-current diodes,diode-connected transistors, or current-regulating diodes.

Esaki or tunnel diodesThese have a region of operation showing negative resistance caused by quantum tunneling,[21] allowingamplification of signals and very simple bistable circuits. Due to the high carrier concentration, tunnel diodesare very fast, may be used at low (mK) temperatures, high magnetic fields, and in high radiationenvironments.[22] Because of these properties, they are often used in spacecraft.

Gunn diodesThese are similar to tunnel diodes in that they are made of materials such as GaAs or InP that exhibit a regionof negative differential resistance. With appropriate biasing, dipole domains form and travel across the diode,allowing high frequency microwave oscillators to be built.

Light-emitting diodes (LEDs)In a diode formed from a direct band-gap semiconductor, such as gallium arsenide, carriers that cross the junction emit photons when they recombine with the majority carrier on the other side. Depending on the material, wavelengths (or colors)[23] from the infrared to the near ultraviolet may be produced.[24] The forward potential of these diodes depends on the wavelength of the emitted photons: 2.1 V corresponds to red, 4.0 V to violet. The first LEDs were red and yellow, and higher-frequency diodes have been developed over time. All LEDs produce incoherent, narrow-spectrum light; "white" LEDs are actually combinations of three LEDs of a

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different color, or a blue LED with a yellow scintillator coating. LEDs can also be used as low-efficiencyphotodiodes in signal applications. An LED may be paired with a photodiode or phototransistor in the samepackage, to form an opto-isolator.

Laser diodesWhen an LED-like structure is contained in a resonant cavity formed by polishing the parallel end faces, alaser can be formed. Laser diodes are commonly used in optical storage devices and for high speed opticalcommunication.

Thermal diodesThis term is used both for conventional p–n diodes used to monitor temperature due to their varying forwardvoltage with temperature, and for Peltier heat pumps for thermoelectric heating and cooling.. Peltier heatpumps may be made from semiconductor, though they do not have any rectifying junctions, they use thediffering behaviour of charge carriers in N and P type semiconductor to move heat.

PhotodiodesAll semiconductors are subject to optical charge carrier generation. This is typically an undesired effect, somost semiconductors are packaged in light blocking material. Photodiodes are intended to senselight(photodetector), so they are packaged in materials that allow light to pass, and are usually PIN (the kind ofdiode most sensitive to light).[25] A photodiode can be used in solar cells, in photometry, or in opticalcommunications. Multiple photodiodes may be packaged in a single device, either as a linear array or as atwo-dimensional array. These arrays should not be confused with charge-coupled devices.

PIN diodesA PIN diode has a central un-doped, or intrinsic, layer, forming a p-type/intrinsic/n-type structure.[26] They areused as radio frequency switches and attenuators. They are also used as large volume ionizing radiationdetectors and as photodetectors. PIN diodes are also used in power electronics, as their central layer canwithstand high voltages. Furthermore, the PIN structure can be found in many power semiconductor devices,such as IGBTs, power MOSFETs, and thyristors.

Schottky diodesSchottky diodes are constructed from a metal to semiconductor contact. They have a lower forward voltagedrop than p–n junction diodes. Their forward voltage drop at forward currents of about 1 mA is in the range0.15 V to 0.45 V, which makes them useful in voltage clamping applications and prevention of transistorsaturation. They can also be used as low loss rectifiers, although their reverse leakage current is in generalhigher than that of other diodes. Schottky diodes are majority carrier devices and so do not suffer fromminority carrier storage problems that slow down many other diodes—so they have a faster reverse recoverythan p–n junction diodes. They also tend to have much lower junction capacitance than p–n diodes, whichprovides for high switching speeds and their use in high-speed circuitry and RF devices such asswitched-mode power supply, mixers, and detectors.

Super barrier diodesSuper barrier diodes are rectifier diodes that incorporate the low forward voltage drop of the Schottky diodewith the surge-handling capability and low reverse leakage current of a normal p–n junction diode.

Gold-doped diodesAs a dopant, gold (or platinum) acts as recombination centers, which helps a fast recombination of minoritycarriers. This allows the diode to operate at signal frequencies, at the expense of a higher forward voltage drop.Gold-doped diodes are faster than other p–n diodes (but not as fast as Schottky diodes). They also have lessreverse-current leakage than Schottky diodes (but not as good as other p–n diodes).[27][28] A typical example isthe 1N914.

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Snap-off or Step recovery diodesThe term step recovery relates to the form of the reverse recovery characteristic of these devices. After aforward current has been passing in an SRD and the current is interrupted or reversed, the reverse conductionwill cease very abruptly (as in a step waveform). SRDs can, therefore, provide very fast voltage transitions bythe very sudden disappearance of the charge carriers.

Stabistors or Forward Reference Diodes

The term stabistor refers to a special type of diodes featuring extremely stable forward voltage characteristics.These devices are specially designed for low-voltage stabilization applications requiring a guaranteed voltageover a wide current range and highly stable over temperature.

Transient voltage suppression diode (TVS)These are avalanche diodes designed specifically to protect other semiconductor devices from high-voltagetransients.[29] Their p–n junctions have a much larger cross-sectional area than those of a normal diode,allowing them to conduct large currents to ground without sustaining damage.

Varicap or varactor diodesThese are used as voltage-controlled capacitors. These are important in PLL (phase-locked loop) and FLL(frequency-locked loop) circuits, allowing tuning circuits, such as those in television receivers, to lock quickly.They also enabled tunable oscillators in early discrete tuning of radios, where a cheap and stable, butfixed-frequency, crystal oscillator provided the reference frequency for a voltage-controlled oscillator.

Zener diodesDiodes that can be made to conduct backward. This effect, called Zener breakdown, occurs at a preciselydefined voltage, allowing the diode to be used as a precision voltage reference. In practical voltage referencecircuits, Zener and switching diodes are connected in series and opposite directions to balance the temperaturecoefficient to near-zero. Some devices labeled as high-voltage Zener diodes are actually avalanche diodes (seeabove). Two (equivalent) Zeners in series and in reverse order, in the same package, constitute a transientabsorber (or Transorb, a registered trademark). The Zener diode is named for Dr. Clarence Melvin Zener ofCarnegie Mellon University, inventor of the device.

Other uses for semiconductor diodes include sensing temperature, and computing analog logarithms (see Operationalamplifier applications#Logarithmic_output).

Numbering and coding schemesThere are a number of common, standard and manufacturer-driven numbering and coding schemes for diodes; thetwo most common being the EIA/JEDEC standard and the European Pro Electron standard:

EIA/JEDECThe standardized 1N-series numbering EIA370 system was introduced in the US by EIA/JEDEC (Joint ElectronDevice Engineering Council) about 1960. Among the most popular in this series were: 1N34A/1N270 (Germaniumsignal), 1N914/1N4148 (Silicon signal), 1N4001-1N4007 (Silicon 1A power rectifier) and 1N54xx (Silicon 3Apower rectifier)[30][31][32]

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JISThe JIS semiconductor designation system has all semiconductor diode designations starting with "1S".

Pro ElectronThe European Pro Electron coding system for active components was introduced in 1966 and comprises two lettersfollowed by the part code. The first letter represents the semiconductor material used for the component (A =Germanium and B = Silicon) and the second letter represents the general function of the part (for diodes: A =low-power/signal, B = Variable capacitance, X = Multiplier, Y = Rectifier and Z = Voltage reference), for example:•• AA-series germanium low-power/signal diodes (e.g.: AA119)•• BA-series silicon low-power/signal diodes (e.g.: BAT18 Silicon RF Switching Diode)•• BY-series silicon rectifier diodes (e.g.: BY127 1250V, 1A rectifier diode)•• BZ-series silicon Zener diodes (e.g.: BZY88C4V7 4.7V Zener diode)Other common numbering / coding systems (generally manufacturer-driven) include:• GD-series germanium diodes (e.g.: GD9) – this is a very old coding system• OA-series germanium diodes (e.g.: OA47) – a coding sequence developed by Mullard, a UK companyAs well as these common codes, many manufacturers or organisations have their own systems too – for example:•• HP diode 1901-0044 = JEDEC 1N4148• UK military diode CV448 = Mullard type OA81 = GEC type GEX23

Related devices•• Rectifier•• Transistor• Thyristor or silicon controlled rectifier (SCR)•• TRIAC•• Diac•• VaristorIn optics, an equivalent device for the diode but with laser light would be the Optical isolator, also known as anOptical Diode, that allows light to only pass in one direction. It uses a Faraday rotator as the main component.

Applications

Radio demodulationThe first use for the diode was the demodulation of amplitude modulated (AM) radio broadcasts. The history of thisdiscovery is treated in depth in the radio article. In summary, an AM signal consists of alternating positive andnegative peaks of a radio carrier wave, whose amplitude or envelope is proportional to the original audio signal. Thediode (originally a crystal diode) rectifies the AM radio frequency signal, leaving only the positive peaks of thecarrier wave. The audio is then extracted from the rectified carrier wave using a simple filter and fed into an audioamplifier or transducer, which generates sound waves.

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Power conversionRectifiers are constructed from diodes, where they are used to convert alternating current (AC) electricity into directcurrent (DC). Automotive alternators are a common example, where the diode, which rectifies the AC into DC,provides better performance than the commutator or earlier, dynamo. Similarly, diodes are also used inCockcroft–Walton voltage multipliers to convert AC into higher DC voltages.

Over-voltage protectionDiodes are frequently used to conduct damaging high voltages away from sensitive electronic devices. They areusually reverse-biased (non-conducting) under normal circumstances. When the voltage rises above the normalrange, the diodes become forward-biased (conducting). For example, diodes are used in (stepper motor andH-bridge) motor controller and relay circuits to de-energize coils rapidly without the damaging voltage spikes thatwould otherwise occur. (Any diode used in such an application is called a flyback diode). Many integrated circuitsalso incorporate diodes on the connection pins to prevent external voltages from damaging their sensitive transistors.Specialized diodes are used to protect from over-voltages at higher power (see Diode types above).

Logic gatesDiodes can be combined with other components to construct AND and OR logic gates. This is referred to as diodelogic.

Ionizing radiation detectorsIn addition to light, mentioned above, semiconductor diodes are sensitive to more energetic radiation. In electronics,cosmic rays and other sources of ionizing radiation cause noise pulses and single and multiple bit errors. This effectis sometimes exploited by particle detectors to detect radiation. A single particle of radiation, with thousands ormillions of electron volts of energy, generates many charge carrier pairs, as its energy is deposited in thesemiconductor material. If the depletion layer is large enough to catch the whole shower or to stop a heavy particle, afairly accurate measurement of the particle’s energy can be made, simply by measuring the charge conducted andwithout the complexity of a magnetic spectrometer, etc. These semiconductor radiation detectors need efficient anduniform charge collection and low leakage current. They are often cooled by liquid nitrogen. For longer-range (abouta centimetre) particles, they need a very large depletion depth and large area. For short-range particles, they need anycontact or un-depleted semiconductor on at least one surface to be very thin. The back-bias voltages are nearbreakdown (around a thousand volts per centimetre). Germanium and silicon are common materials. Some of thesedetectors sense position as well as energy. They have a finite life, especially when detecting heavy particles, becauseof radiation damage. Silicon and germanium are quite different in their ability to convert gamma rays to electronshowers.Semiconductor detectors for high-energy particles are used in large numbers. Because of energy loss fluctuations,accurate measurement of the energy deposited is of less use.

Temperature measurementsA diode can be used as a temperature measuring device, since the forward voltage drop across the diode depends ontemperature, as in a silicon bandgap temperature sensor. From the Shockley ideal diode equation given above, itmight appear that the voltage has a positive temperature coefficient (at a constant current), but usually the variationof the reverse saturation current term is more significant than the variation in the thermal voltage term. Most diodestherefore have a negative temperature coefficient, typically −2 mV/˚C for silicon diodes at room temperature. This isapproximately linear for temperatures above about 20 kelvins. Some graphs are given for: 1N400x [33] series, andCY7 cryogenic temperature sensor [34].

Diode 14

Current steeringDiodes will prevent currents in unintended directions. To supply power to an electrical circuit during a power failure,the circuit can draw current from a battery. An uninterruptible power supply may use diodes in this way to ensurethat current is only drawn from the battery when necessary. Likewise, small boats typically have two circuits eachwith their own battery/batteries: one used for engine starting; one used for domestics. Normally, both are chargedfrom a single alternator, and a heavy-duty split-charge diode is used to prevent the higher-charge battery (typicallythe engine battery) from discharging through the lower-charge battery when the alternator is not running.Diodes are also used in electronic musical keyboards. To reduce the amount of wiring needed in electronic musicalkeyboards, these instruments often use keyboard matrix circuits. The keyboard controller scans the rows andcolumns to determine which note the player has pressed. The problem with matrix circuits is that, when several notesare pressed at once, the current can flow backwards through the circuit and trigger "phantom keys" that cause "ghost"notes to play. To avoid triggering unwanted notes, most keyboard matrix circuits have diodes soldered with theswitch under each key of the musical keyboard. The same principle is also used for the switch matrix in solid-statepinball machines.

AbbreviationsDiodes are usually referred to as D for diode on PCBs. Sometimes the abbreviation CR for crystal rectifier isused.[35]

Two-terminal nonlinear devicesMany other two-terminal nonlinear devices exist, for example a neon lamp has two terminals in a glass envelope andhas interesting and useful nonlinear properties. Lamps including arc-discharge lamps, incandescent lamps,fluorescent lamps and mercury vapor lamps have two terminals and display nonlinear current–voltagecharacteristics.

References[1] Tooley, Mike (2012). Electronic Circuits: Fundamentals and Applications, 3rd Ed. (http:/ / books. google. com/

books?id=NunPn6R__TAC& pg=PA81& dq=diode+ cathode+ anode+ n-type). Routlege. pp. 81. ISBN 1136407316. .[2] Lowe, Doug (2013). "Electronics Components: Diodes" (http:/ / www. dummies. com/ how-to/ content/ electronics-components-diodes.

html). Electronics All-In-One Desk Reference For Dummies. John Wiley & Sons. . Retrieved January 4, 2013.[3] Crecraft, David; Stephen Gergely (2002). Analog Electronics: Circuits, Systems and Signal Processing (http:/ / books. google. com/

books?id=lS7qN6iHyBYC& pg=PA110& dq=diode+ cathode+ anode+ n-type+ p-type). Butterworth-Heinemann. pp. 110. ISBN 0750650958..

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books?id=09Zsv97IH1MC& pg=PA88). IEEE Transactions on Microwave Theory and Techniques 45 (12): 2267–2273.Bibcode 1997ITMTT..45.2267E. doi:10.1109/22.643830. . Retrieved 2010-01-19.

Diode 15

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[15] U.S. Patent 836,531 (http:/ / www. google. com/ patents?vid=836531)[16] "Electronic Valve - AWV,Diode, Type 6AU5GTA" (http:/ / museumvictoria. com. au/ collections/ items/ 414981/

electronic-valve-awv-diode-type-6au4gta-1960-1965). Museum Victoria. . Retrieved 9 January 2013.[17][17] citation needed[18] (http:/ / ecee. colorado. edu/ ~ecen5817/ hw/ hw1/ Diode reverse recovery in a boost converter. pdf)[19] (http:/ / ecee. colorado. edu/ ~ecen5797/ course_material/ SwLossSlides. pdf)[20] Current regulator diodes (http:/ / digikey. com/ Web Export/ Supplier Content/ Vishay_8026/ PDF/ Vishay_CurrentRegulatorDiodes. pdf)[21] Jonscher, A. K. The physics of the tunnel diode. British Journal of Applied Physics 12 (Dec. 1961), 654–659.[22] Dowdey, J. E., and Travis, C. M. An analysis of steady-state nuclear radiation damage of tunnel diodes. IRE Transactions on Nuclear

Science 11, 5 (November 1964), 55–59.[23] Classification of components (http:/ / digikey. com/ Web Export/ Supplier Content/ Vishay_8026/ PDF/

Vishay_ClassificationOfComponents. pdf)[24] "Component Construction" (http:/ / www. element-14. com/ community/ docs/ DOC-22517/ l/

component-construction--vishay-optoelectronics). 2010-05-25. . Retrieved 2010-08-06.[25] Component Construction (http:/ / digikey. com/ Web Export/ Supplier Content/ Vishay_8026/ PDF/ Vishay_ComponentConstruction. pdf)[26] "Physics and Technology" (http:/ / www. element-14. com/ community/ docs/ DOC-22516/ l/

physics-and-technology--vishay-optoelectronics). 2010-05-25. . Retrieved 2010-08-06.[27] Fast Recovery Epitaxial Diodes (FRED) Characteristics - Applications - Examples (http:/ / www. ixyspower. com/ images/

technical_support/ Application Notes By Topic/ FREDs, Schottky and GaAS Diodes/ IXAN0044. pdf)[28] S. M. Sze, Modern Semiconductor Device Physics, Wiley Interscience, ISBN 0-471-15237-4[29] Protecting Low Current Loads in Harsh Electrical Environments (http:/ / digikey. com/ Web Export/ Supplier Content/ Vishay_8026/ PDF/

Vishay_ProtectingLowCurrentLoads. pdf)[30] "About JEDEC" (http:/ / www. jedec. org/ Home/ about_jedec. cfm). Jedec.org. . Retrieved 2008-09-22.[31] "EDAboard.com" (http:/ / news. elektroda. net/ introduction-dates-of-common-transistors-and-diodes-t94332. html). News.elektroda.net.

2010-06-10. . Retrieved 2010-08-06.[32] I.D.E.A. "Transistor Museum Construction Projects Point Contact Germanium Western Electric Vintage Historic Semiconductors Photos

Alloy Junction Oral History" (http:/ / semiconductormuseum. com/ Museum_Index. htm). Semiconductormuseum.com. . Retrieved2008-09-22.

[33] http:/ / www. cliftonlaboratories. com/ 1n400x_diode_family_forward_voltage. htm[34] http:/ / www. omega. com/ Temperature/ pdf/ CY7. pdf[35] John Ambrose Fleming (1919). The Principles of Electric Wave Telegraphy and Telephony (http:/ / books. google. com/

books?id=xHNBAAAAIAAJ& pg=PA550& dq="crystal+ rectifier"+ CR& as_brr=1). London: Longmans, Green. p. 550. .

External links• Diodes and Rectifiers (http:/ / www. allaboutcircuits. com/ vol_3/ chpt_3/ 1. html) - Chapter on All About

Circuits

Interactive and animations• Interactive Explanation of Semiconductor Diode (http:/ / www-g. eng. cam. ac. uk/ mmg/ teaching/ linearcircuits/

diode. html), University of Cambridge• Schottky Diode Flash Tutorial Animation (http:/ / www. ee. byu. edu/ cleanroom/ schottky_animation. phtml)

Article Sources and Contributors 16

Article Sources and ContributorsDiode  Source: http://en.wikipedia.org/w/index.php?oldid=532662257  Contributors: 15.253, 165.123.179.xxx, 203.37.81.xxx, 208.187.134.xxx, 209.130.132.xxx, AK456, Abu-Fool Danyal ibnAmir al-Makhiri, Acather96, Acronymsical, Ahoerstemeier, Ajitkumar 2009, Akash96, Alansohn, Aldie, Aledeniz, Alejo2083, Alfred Centauri, [email protected], Allens, Amr Bekhit, Amram99,Andante1980, Andries, Arch dude, Archimerged, ArdWar, Arisharon, Ark2120, Arnero, Arpit.withu, Atlant, Audriusa, Aulis Eskola, Authalic, Avin, Az1568, Balavenkataraju, Bassington,Bbatsell, Bboothman, Behnammirzay, Bert490, Bggoldie, Biscuittin, Blainster, Blink, Bmwtroll, Bogdangiusca, Bongomatic, Bongwarrior, Bookandcoffee, Braincricket, Branddobbe, BrandonHixson, Brews ohare, BrightStarSky, Brighterorange, CJLL Wright, Cal 1234, Camayoc, Can't sleep, clown will eat me, Capricorn42, Cdc, Chendy, Chetvorno, Cirrone, Coffee, Colossuskid,Conversion script, Corruptcopper, Cpl Syx, Cronium, CyrilB, DARTH SIDIOUS 2, DV8 2XL, Dahamsta, Daniele.tampieri, Darein, Darkhorse, Darth Panda, Davdforg, David R. Ingham,Deadferrets, Deor, Dgrant, Dicklyon, Djordjes, Donarreiskoffer, Drphilharmonic, Dysprosia, EL Willy, Eadthem, Eddiehimself, Edward, Elbreapoly, Electron9, Em3ryguy, EmadIV, Epbr123,Erik Streb, Ertyiopul8, Escape Orbit, Espencer, F-402, Falcon8765, Farideh.soheily, Favonian, Fernblatt, Fisherjs, Flubbit, FocalPoint, Foobaz, Forum Mod Daniel, Frappyjohn, Fresheneesz,Furrykef, GRAHAMUK, GRider, Geheimer, Gene Nygaard, GeoGreg, Geobio, Gerry Ashton, Giftlite, Gilliam, Gimmetrow, Glane23, Glenn, Glogger, Gogo Dodo, Goudzovski, Graham87,Gruu, Gurch, H1voltage, Haham hanuka, Hashemfekry9, Headbomb, HenryLi, Heron, Hooperbloob, Hurricane111, ILike2BeAnonymous, INkubusse, J.delanoy, Jackandbos, JamesBWatson,Jason Leach, Jauhienij, Jay-Sebastos, Jerzy, Jhabib, JimVC3, Jimp, Jll, Jobberone, Jobetheren, John Dalton, John Reid, John of Reading, Johnflux, Johnmathew15, JohnnyKegs, Jojit fb,Joshuachohan, Jp314159, Jp619, Jwheimans, Kartano, Karthiksperla, Katalaveno, Kb1koi, Kevca, Kevinpurcell, Kingpin13, Knutux, KonaBear05, Koumz, KrakatoaKatie, Kreline, Kristleifur,Kurykh, KyraVixen, Lazulilasher, Learner71, Ledgerbob, Leonard G., Light current, LilHelpa, Lindosland, Lindseyrose, Lion789, Lionoche, Lissajous, LittleOldMe, LizardJr8, Lovro, MER-C,MKoltnow, MPerel, Maitchy, Mako098765, Manastuna, MarkEaston, MarsRover, Mataresephotos, Materialscientist, Matt Britt, Maxdlink, Maximus Rex, Maxis ftw, Mbc362, Melchoir,Mephistophelian, Mholland, Michael Hardy, Migul91, Mikhail Ryazanov, Mikiemike, Mild Bill Hiccup, Mimarx, Mindmatrix, Mkratz, Mo0, Morcheeba, Mortivik, Mrseanski, Msdaif, Mssetiadi,Mstrogoff, Mthardy, Mudlock, Nabla, Nanzilla, Naseh nezami, Nczempin, Nedim Ardoğa, Nestorius, Nextext, Nhoss2, Nick Number, NickW557, Nigelj, Niimiish, Nikai, Nimur, Nkendrick,Nonforma, Nopetro, Norkimes, Okedem, Olfzwin, Oliver Sedlacek, Omegatron, Omicronpersei8, OnBeyondZebrax, Opelio, Ovis23, Oxymoron83, PHaze, Padre31, Pandamonia, Paultseung,Pawan vaskar, Philip Trueman, Photodude, Pi.1415926535, Pi3832, Pinethicket, Pjrm, Plober, Poetman22, Pol098, Possum, Pringley Joe, ProperFraction, Publicly Visible, Puelly, Puffin, Quibik,QuiteUnusual, Qwertymnbvc10, R'n'B, R-Joe, R6144, Rbj, Re bill seeker of archery, Rees11, RexNL, Rfl, Rholton, Riana, Richard416282, Richmd, Riflemann, Rjstott, Rogerbrent, Rohitbd,Roman12345, Ross Burgess, Rror, Rwalker, Ryan Norton, S3nbon5akura, SQL, SahRaeH, Salvio giuliano, Sam Blacketer, Sam Gardiner, Sam Hocevar, Savastio, Sbmeirow, Schroedi,Scopeknowledge, Searchme, Sesc, Shekhartit, Shocking Asia, Sietse Snel, Silverxxx, Sir Vicious, Siyamraj, Skizzik, Slowking Man, Smee78, SmoJoe, Smooth O, Snailwalker, Snoyes, Some jerkon the Internet, Sonygal, SpaceFlight89, Speedevil, Spiel496, Springnuts, Srleffler, SteveW, Sthubertus, Stovetopcookies, StradivariusTV, StuartH, Svick, Symane, Syndicate, Tabby, Tarchon,Tasc, TedPavlic, Thatguyflint, The Lightning Stalker, The Photon, TheDog, TheNoise, Theresa knott, Thingg, Tide rolls, Tim Starling, Timwi, Titodutta, Tls60, Tobias Hoevekamp, Tom.Reding,Tomchiukc, Tony Sidaway, Topory, TreeSmiler, Treisijs, Tresiden, TrevorP, Tzarius, Ulfbastel, Ulrich67, Ultramince, Unyoyega, Us441, Username1507, Vedant, Ventusa, Versus22,Vipinratnakaran, VladimirKorablin, W0lfie, WLU, Wavelength, Wbm1058, Weetoddid, Why Not A Duck, Widr, Wiki alf, Wikipelli, Wjbeaty, Wolfoftheazuresky, Wstorr, Wtshymanski,Xezbeth, Xitdiest0day, Xoristzatziki, Youandme, Zee1215, Zfr, Zotel, Zundark, Zvika, Пика Пика, محبوب عالم, రవిచంద్ర, 873 anonymous edits

Image Sources, Licenses and ContributorsImage:Diode-closeup.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Diode-closeup.jpg  License: Creative Commons Attribution-Sharealike 2.5  Contributors: Original uploader wasMorcheeba at en.wikipediaImage:Dioden2.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Dioden2.jpg  License: GNU Free Documentation License  Contributors: UlfbastelImage:Diode tube schematic.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Diode_tube_schematic.svg  License: Creative Commons Attribution-Sharealike 2.5  Contributors:OjibberishImage:Vacuum diode.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Vacuum_diode.svg  License: Creative Commons Attribution-ShareAlike 3.0 Unported  Contributors:Riflemann, WikipediaMaster, ГороватоImage:Diode symbol.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Diode_symbol.svg  License: GNU Free Documentation License  Contributors: Created by User:OmegatronImage:LED symbol.svg  Source: http://en.wikipedia.org/w/index.php?title=File:LED_symbol.svg  License: GNU Free Documentation License  Contributors: Er Komandante, Jed, Omegatron,Papa November, Rocket000, Sergey kudryavtsev, 11 anonymous editsImage:Photodiode symbol.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Photodiode_symbol.svg  License: GNU Free Documentation License  Contributors: Omegatron,Rocket000, Sergey kudryavtsev, 5 anonymous editsImage:Schottky diode symbol.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Schottky_diode_symbol.svg  License: GNU Free Documentation License  Contributors: Dmitry G,Gvf, Omegatron, ProtocolOH, Rocket000, WikipediaMaster, 2 anonymous editsImage:Transient voltage suppression diode symbol.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Transient_voltage_suppression_diode_symbol.svg  License: Public Domain Contributors: Albedo-ukr, Glenn, Rocket000, W0lfie, 1 anonymous editsImage:Tunnel diode symbol.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Tunnel_diode_symbol.svg  License: GNU Free Documentation License  Contributors: Albedo-ukr,Chetvorno, Glenn, Omegatron, Rocket000, WikipediaMasterImage:Varicap symbol.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Varicap_symbol.svg  License: GNU Free Documentation License  Contributors: Omegatron, Rocket000,Sergey kudryavtsev, Tothwolf, 2 anonymous editsImage:Zener_diode_symbol.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Zener_diode_symbol.svg  License: GNU Free Documentation License  Contributors: Cflm001,Omegatron, Rocket000, Sergey kudryavtsev, 6 anonymous editsImage:Diode pinout en fr.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Diode_pinout_en_fr.svg  License: Creative Commons Attribution-Sharealike 3.0,2.5,2.0,1.0  Contributors:Erik StrebFile:Diode-IV-Curve.svg  Source: http://en.wikipedia.org/w/index.php?title=File:Diode-IV-Curve.svg  License: Creative Commons Attribution-Sharealike 3.0  Contributors: H1voltageImage:Diodes.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Diodes.jpg  License: GNU Free Documentation License  Contributors: Mysid, OmegatronImage:DO-41 Dimensions.svg  Source: http://en.wikipedia.org/w/index.php?title=File:DO-41_Dimensions.svg  License: Public Domain  Contributors: Inductiveload

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