snubber

snubberSnubberCircuit2021-12-0809:56缓冲电路（SnubberCircuit）又称为吸收电路。其中的电阻和电容分别称为缓冲电阻（snubberresistence）和缓冲电容（Snubbercapacitance）。其作用是抑制电力电子器件的内因过电压、du/dt或者过电流di/dt,减小器件的开关损耗。缓冲电路可分为关断缓冲电路和开通缓冲电路。关断缓冲电路又称为du/dt抑制电路，用于吸收器件的关断过电压和换相过电压，抑制du/dt，减小关断损耗。开通缓冲电路又称为di/dt，用于抑制器件开通时的电流过冲和di/dt，减小器件的开通损耗。可将关断缓冲电路和开通缓冲电路结合在一起，称其为复合缓冲电路。还可以用另外的分类方法：缓冲电路中储能元件的能量如果消耗在其吸收电阻上，则称其为耗能式缓冲电路；如果缓冲电路能将其储能元件的能量回馈给负载或电源，则称其为馈能式缓冲电路，或称为无损吸收电路。SnubberFromWikipedia,thefreeencyclopediaElectricalsystemsSnubbersarefrequentlyusedinelectricalsystemswithaninductiveloadwherethesuddeninterruptionofcurrentflowwouldleadtoasharpriseinvoltageacrossthedevicecreatingtheinterruption.Thissharpriseinvoltagemightleadtoatransientorpermanentfailureofthecontrollingdevice.Asparkislikelytobegenerated(arcing)andtocauseelectromagneticinterference.Thesnubberpreventsthisundesiredvoltagebyconductingtransientcurrentaroundthedevice.[edit]RCsnubbersRCsnubbersAsimplesnubbercomprisingasmallresistor(R)inserieswithasmallcapacitor(C)isoftenused.Thiscombinationcanbeusedtosuppress（抑制）therapid（快速）riseinvoltageacrossathyristor,preventingtheerroneousturn-onofthethyristor;itdoesthisbylimitingtherateofriseinvoltage(dV/dt)acrossthethyristortoavaluewhichwillnottriggerit.Snubbersarealsooftenusedtopreventarcingacrossthecontactsofrelaysandswitchesandtheelectricalinterferenceandwelding/stickingofthecontactsthatcanoccur.Anappropriately-designedRCsnubbercanbeusedwitheitherdcoracloads.Thissortofsnubberiscommonlyusedwithinductiveloadssuchaselectricmotors.Thevoltageacrossacapacitorcannotchangeinstantaneously,soadecreasingtransientcurrentwillflowthroughitforasmallfractionofasecond,allowingthevoltageacrosstheswitchtoincreasemoreslowlywhentheswitchisopened.Whilethevaluescanbeoptimisedfortheapplication,a100ohmresistorinserieswitha100nanofaradcapacitorofappropriatevoltageratingisusuallyeffective.Thistypeofsnubberisoftenmanufacturedasasinglecomponent.[edit]DiodesnubbersMainarticle:flybackdiodeWhenthecurrentflowingisDC,asimplerectifierdiodeisoftenemployedasanotherformofsnubber.Thesnubberdiodeiswiredinparallelwithaninductiveload(suchasarelaycoilorelectricmotor).Thediodeisinstalledsothatitdoesnotconductundernormalconditions.Whencurrenttotheinductiveloadisrapidlyinterrupted,alargevoltagespikewouldbeproducedinthereversedirection(astheinductorattemptstokeepcurrentflowinginthecircuit).Thisspikeisknownasaninductivekick.Placingthesnubberdiodeininverseparallelwiththeinductiveloadallowsthecurrentfromtheinductortoflowthroughthedioderatherthanthroughtheswitchingelement,dissipatingtheenergystoredintheinductiveloadovertheseriesresistanceoftheinductorandthe(usuallymuchsmaller)resistanceofthediode(over-voltageprotection).Onedisadvantageofsimplerectifierdiodeusedasasnubberisthatthediodeallowscurrenttocontinueflowing,whichmaycausetherelaytoremainactuatedforslightlylonger;somecircuitdesignsmustaccountforthisdelayinthedropping-outoftherelay.[edit]More-sophisticatedsolid-statesnubbersInsomedccircuits,avaristorortwoinverse-seriesZenerdiodes(collectivelycalledatransorb)maybeusedinsteadofthesimplediode.Becausethesedevicesdissipatesignificantpower,therelaymaydrop-outfasterthanitwouldwithasimplerectifierdiode.Anadvantagetousingatransorboverjustonediodehowever,isthatitwillprotectagainstbothoverandundervoltageifconnectedtoground,forcingthevoltagetostaybetweentheconfinesofthebreakdownvoltagesoftheZenerdiodes.JustoneZenerdiodeconnectedtogroundwillonlyprotectagainstpositivetransients.Inaccircuitsarectifierdiodesnubbercannotbeused;ifasimpleRCsnubberisnotadequateamorecomplexbidirectionalsnubberdesignmustbeused.