01 of 07Version 2010

What is a ResistorTOKEN

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What is a Resistor

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Resistor is electrical or electronic components whichresisttheflowofcurrentacrosstheresistordevice.

Theresistancetocurrentflowresultsinavoltage dropacrosstheresistordevice.Resistorsareused extensivelythroughoutelectricalandelectronicircuits.

Resistordevicesmayprovideafixed,variable,oradjustable valueofresistance.Adjustableresistorsarereferstoasostats, oriometers.ResistorvaluesareexpressedinOhms, thelectricresistanceunit.

Resistorsareincorporatedwithinaelectricalorelectroniccircuit createaknownvoltagedroporcurrenttovoltagerelationship.Iftheelectricalcurrentinacircuitisknown(currentismeasuredinamperes),thenaresistorcanbeusedtocreateaknownpotentialdifference(voltagedifference)proportionaltothatcurrent.Conversely,ifthevoltagedrop(potentialdifference)acrosstwopointsinacircuitisknown,aresistorcanbeusedtocreateaknowncurrentproportionaltothatdifference.

Anattenuatorisanetworkoftwoormoreresistors(avoltagedivider).Alineterminatorisaresistorattheendofatransmissionlineordaisychainbus,designedtomatchimpedanceandminimizereflectionsoftheelectronicsignal.

02 of 07

WhatisOhm’sLaw?

Version 2010

What is a ResistorTOKEN

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Ohm’slawisasimpleequationthatshowstherelationshipbetweenresistance,voltageandcurrentthroughametalwire,orsomeothertypeofresistivematerial.Inmathematicalterms,Ohm’slawiswrittenas:

I = V/R , whereIisthecurrent(Amps),Visthevoltage(Volts),andRistheresistance(Ohms).

P = Watts

Watts Volts X Amperes

Watts = Amperes2 X Ohms

Watts =

V = Volts

Volts = √ Watts X Ohms

Volts =

Volts = Ohms X Amperes

Volts2

Ohms

WattsAmperes

I = Amperes

Amperes =WattsOhms

Amperes = VoltsOhms

Amperes = WattsVolts

√

R = Ohms

Ohms = Volts

Amperes

Ohms = Watts

Amperes2

Ohms =Volts2

Watts

V*II2 *R

V2/R

P/II*R V*I

V2/P

P/I2

P/VV/R

P*R√

I

R

Amps

Ohms

P

V

Watts

Volts

P/R√

Ohm’slawcanalsoshowtherelationshipbetweenresistance,voltageandpowerusingthefollowingequation:

P = V2 /R ,wherePisthepower(Watts),Visthevoltage(Volts),andRistheresistance(Ohms).

03 of 07Version 2010

What is a ResistorTOKEN

MetalOxideResistorsAtypeofcylindricalresistorthatusesmaterialssuchasrutheniumoxideortinoxideastheresistiveelement.Theseresistorscanbeexcellenthigh-voltageorhigh-powerdevices.

Thick Film ResistorsSpeciallybuiltsurface-mountfilmresistorthatcarrieshighpowerforthepartsize.Forthickfilmresistors,arutheniumoxidefilmormetalglazefilmisappliedusingtraditionalscreen-printingtechnology.Theseresistorfilmcanbeexcellenthigh-voltageorhigh-powerdevices.

ThinFilmResistorsAtypeofsurface-mountfilmresistorwitharelativelythinresistiveelement,measuredinangstroms(millionthsofaninch).Thinfilmresistorsaremadebysputtering(alsoknownasvacuumdeposition)aresistivematerial,suchasnichromeortantalumnitride,ontothesurfaceofasubstrate.

Metal-FilmResistorsAtypeofcylindricalresistorsmadebydepositingaresistiveelementmadeofathinconductingfilmofametalormetalalloy,suchasnichrome,ontoacylindricalceramicorglasscore.Theresistanceiscontrolledbycuttingahelicalgroovethroughtheconductingfilm.

TypesofResistors

FixedResistorsAfixedresistorisoneinwhichthevalueofitsresistancecannotchange.

Non-LinearResistorsAnon-linearresistorisaresistorthathasresistancesthatvarysignificantlywithappliedvoltage,temperatureorlight.Typesofnon-linearresistorsarevaristors,thermistorsandphotoresistors.

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CarbonCompositionResistorsAgeneralclassdescriptionforresistorsconsistingofacarbonmixtureresistivecoreandamoldedouterinsulatingcore.

CeramicCompositionResistorsAtypeofresistorthatconsistsofaclay,alumina,andcarbonmixturethathasbeenblendedandpressurizedintoaresistivecoreandthencoveredwithamoldedouterinsulatingcore.

CarbonFilmResistorsAgeneralclassdescriptionforcylindricalresistorsmadebydepositingacarbonfilmonthesurfaceofacentercoreinsulator.

04 of 07 Version 2010

What is a ResistorTOKEN

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WirewoundResistorsConsistofacylindricalcorewhichiswrappedorwoundwithwire.Thecylindricalcoreistypicallymadefromaceramic,plastic,orfiberglasscorematerial.Thewireisatypeofresistancewire,suchasnichrome.Wirewoundresistorsareatypeofpowerresistorandareaccurate.Wirewoundresistorsareavailableasfixed,oradjustabletobeusedasarheostatorpotentiometer.Typicalapplicationforwirewoundresistorsincludedevicerequiringhighcurrenthandlingcapability,heatdissipationandresistancestabilityandaccuracy.

HighPrecisionResistors

Avarietyoftestinstrumentsrelyonstable,lowTCR,HighaccuracyResistivedevicesforuseasreferencedevicesintheircircuits.

Whiletherearelowcostmetalfilm,chipdevices,andwirewoundresistorswhichofferthedesiredcharacteristics,Token’sThin-FilmtechnologyisuniqueintheirperformanceastheycouldofferveryhighstabilitywithverylowTCR’sandtheabilitytogivealongdriftfreeservice.

NeutralGroundingResistorsNeutralgroundingresistorsareincorporatedintoelectricalcircuitstoprotectthesystemanddevices.Neutralgroundingresistorsprotectelectricalcircuitcomponentsbylimitingthegroundfaultcurrenttoanacceptablelevel.Withinthreephaseelectricvoltagesystem,theneutralbranchisreferencedtoground(earth).Intheeventthatacurrentfaultoccurs(shorttoground),extremecurrentcausesbythefaultwilldamageelectricalcircuitsystemandcomponents.Byinstallinganeutralgroundingresistor,thefaultycurrentwillbelimitedtoapredeterminedlevel.

What is a ResistorTOKENDynamicBrakingResistorDynamicBrakingResistorisahighpower/wattageresistorusedbyaelectricmotortoassistintheprocessknownasdynamicbraking.

DCmotors,unlikeACmotors,actlikeaelectricalgeneratorwhenthemotorhasbeendisconnectedfromthepowersource.ThemotorfunctionslikeageneratorduetotheDCmotorspermanentmagnet.Theresistancetorotationcausesthedynamicbraking.ThevoltageandcurrentproducedbytheDCmotorgenerator)isdirectedintothedynamicbrakingresistortodissipatetheheatenergy.

Installationdesignconsiderations:Dynamicbrakingresistorsshouldbelocatedandmountedintothetargetassemblysuchthatmaximumthermaldissipationthroughtheresistordevicemayoccur.Thermaldissipationwilldependontheresistorselectedandthepowerapplicationdutycycle.Careshouldbetakentoensurethebrakingresistorinstallationisclearofcombustiblematerials.

PowerResistorsPowerResistorsareresistorswhicharecapableofhandlingalotofpower,astheirnameimplies.Theyaredesignedandmanufacturedtohandlemorepowerwithrespecttotheirsizethanotherresistorstypes.Powerresistorsaremanufacturedinavarietyofconfigurations.Someofpowerresistorsarefreewoundsimilartoaelectricalheater element.Freewoundpowerresistorstypicallyrequireexternalsourcesofcoolinginordertohandleanysignificantamountofpower.Powerresistorsmaybecooledbyfans,orimmersedinanon-conductiveliquid.

Powerresistorsaredesignedtooperateatmaximumpowerratinginthesmallestpackagesize,thecoreonwhichthewindingsaremadeisamaterialwhichexhibitsahighheatconductivity.Typicalpowerresistorcoresforwouldtypepowerresistorsare;Steatite,Alumina,BerylliumOxide,orhardanodizedAluminum.Powerresistorsareavailableinvariousshapes,suchas;oval,flat,orcylindrical.Often,powerresistorsarepackagedorintegratedwithaconvectiontypeheatsink.

05 of 07Version 2010 http://www.token.com.tw/ rfq token.com.tw

What is a ResistorTOKEN

RheostatArheostatisanelectricalcomponentthathasanadjustableresistance.Itisatypeofpotentiometerthathastwoterminalsinsteadofthree.Thetwomaintypesofrheostataretherotaryandslider.Thesymbolforarheostatisaresistorsymbolwithanarrowdiagonallyacross it.Theyareusedinmanydifferentapplications,fromlightdimmerstothemotorcontrollersinlargeindustrialmachines.

TheRheostatisthesimplestwayofusingavariableresistor.Twoterminalsareused:oneconnectedtoanendofthetrack,theothertothemoveablewiper.Turningthespindlechangestheresistancebetweenthetwoterminalsfromzerouptothemaximumresistance.

Rheostatsareoftenusedtovarycurrent,forexampletocontrolthebrightnessofalamportherateatwhichacapacitorcharges.

Therheostatisstillacommonandfundamentalelectroniccomponentusedtocontroltheflowofcurrentinacircuit.However,ithaslargelybeenreplacedbythetriac,asolid-statedevicealsoknownasasiliconcontrolledrectifier(SCR).Atriacdonotwasteasmuchpowerasarheostatandhasbetterreliabilityduetotheabsenceofmechanicalparts.Rheostatscommonlyfailbecausetheircontactsbecomedirtyorthecoilwirecorrodesandbreaks.

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VariableResistorsVariableresistorsconsistofaresistancetrackwithconnectionsatbothendsandawiperwhichmovesalongthetrackasyouturnthespindle.Thetrackisusuallyrotarybutstraighttrackversions,usuallycalledsliders,arealsoavailable.Thetrackmaybemadefromcarbon,cermet(ceramicandmetalmixture)oracoilofwire(forlowresistances).

Variableresistorsareoftencalledpotentiometersinbooksandcatalogues.Theyarespecifiedbytheirmaximumresistance,linearorlogarithmictrack,andtheirphysicalsize.

Variableresistorsmaybeusedasarheostatwithtwoconnections(thewiperandjustoneendofthetrack)orasapotentiometerwithallthreeconnectionsinuse.

Miniatureversionscalledpresetsaremadeforsettingupcircuitswhichwillnotrequirefurtheradjustment.

What is a ResistorTOKEN

07 of 07Version 2010 http://www.token.com.tw/ rfq token.com.tw

PotentiometerVariableresistorsusedaspotentiometershaveallthreeterminalsconnected.Thisarrangementisnormallyusedtovaryvoltage,forexampletosettheswitchingpointofacircuitwithasensor,orcontrolthevolume(loudness)inanamplifiercircuit.Iftheterminalsattheendsofthetrackareconnectedacrossthepowersupplythenthewiperterminalwillprovideavoltagewhichcanbevariedfromzerouptothemaximumofthesupply.

PresetsTheseareminiatureversionsofthestandardvariableresistor.Theyaredesignedtobemounteddirectlyontothecircuitboardandadjustedonlywhenthecircuitisbuilt.Forexampletosetthefrequencyofanalarmtoneorthesensitivityofalight-sensitivecircuit.Asmallscrewdriverorsimilartoolisrequiredtoadjustpresets.

Presetsaremuchcheaperthanstandardvariableresistorssotheyaresometimesusedinprojectswhereastandardvariableresistorwouldnormallybeused.

MultiturnpresetsMultiturnPresetsareusedwhereverypreciseadjustmentsmustbemade.Thescrewmustbeturnedmanytimes(10+)tomovethesliderfromoneendofthetracktotheother,givingveryfinecontrol.

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