PNPVSNPN:Workingprinciple,instructions
Thetriodeisthemostimportantdeviceinanelectroniccircuit,anditsmainfunctioniscurrent amplificationandswitching
Therearetwotypesoftriodes:germaniumtubesandsilicontubesEachofthemhastwo structuralforms,NPNandPNP,butthemostcommonlyusedtransistorsaresiliconNPNandPNP. Bothofthemhavethesameworkingprincipleexceptforthepolarityofthepowersupply
Thecommontriodesare9012,s8550,9013,bd140ands8050Themainfunctionofthetriodein thesingle-chipmicrocomputerapplicationcircuitistheswitchingfunction.Amongthem,9012 and8550arepnptransistors,whichcanbeuseduniversallyAmongthem,9013and8050are npntypetransistors,whichcanbeuseduniversally.
TheNPNtransistorconsistsoftwoN-typesemiconductorsandoneP-typesemiconductor,with theP-typesemiconductorinthemiddleandtwoN-typesemiconductorsonbothsides
ThePNP-typetransistorisatransistorcomposedoftwoP-typesemiconductorssandwichingan N-typesemiconductor,soitiscalledaPNP-typetransistorItcanalsobedescribedasatriode wherecurrentflowsfromtheemitterE
Theworkingprincipleofthetriode
Theprincipleofthetriodehasthreeworkingstates:cut-off,amplification,andsaturation.The enlargedstateismainlyusedinanalogcircuits,andtheusageandcalculationmethodsare relativelycomplicated,sowewillnotuseittemporarily.Thedigitalcircuitmainlyusesthe switchingcharacteristicsofthetriode,andonlyusesthetwostatesofcut-offandsaturation
WhatwegenerallycallanordinarytriodeisadevicewithcurrentamplificationOthertriodes alsoextendtheirfunctionsbasedonthisprinciple.Thestructureandsymbolofthetriodeare showninthefigurebelow
NPNandPNParemainlydifferentinthedirectionofcurrentandthe positiveandnegativevoltage
HerewetaketheNPNtriodeasanexampletoexplainitsworkingprinciple
ItisadevicethatdrivesthecurrentIcflowingthroughcewithb(base) currentIb,anditsworkingprincipleisverysimilartoacontrollable valve.
Thesmallbluewaterflowimpulseleverinthethintubeontheleftwidens thevalveofthelargewaterpipe,allowingalargerflowofredwater topassthroughthevalve.Whenthebluewaterflowislarger,thered waterflowinthelargepipeisalsolarger.Ifthemagnificationis100, thenwhenthesmallbluewaterflowis1kg/hr,thenthebigpipeisallowed toflow100kg/hrofwater.Similarly,whenthemagnificationofthetriode is100andIb(basecurrent)is1mA,acurrentof100mAisallowedtopass throughIce.Theworkingprinciplesofthetwotriodesaresummarizedas follows:theemitter(e)oftheNPNisgrounded,thecollector(c)is connectedtoahighlevel,thebase(b)isconnectedtothecontrolsignal, andthecurrent(Ib)ofb-eisusedtocontrolthecurrentofc-e(Ic), thepotentialoftheepoleisthelowest,andthepotentialofthecpole isusuallythehighestduringnormalamplification,thatis,Vc>Vb> VeThetriodeisturnedon,andthecurrentflowsfromthecpoletothe epole.Theemitter(e)ofPNPisconnectedtothehighlevel,thecollector (c)isconnectedtoalowlevel,thebase(b)isconnectedtothecontrol signal,andthecurrent(Ib)ofe-bisusedtocontrolthecurrent(Ic) ofe-c,andthepotentialofe-poleisthehighest,andthec-pole potentialisusuallythelowestduringnormalamplification,thatis,Vc <Vb<Ve.Thetriodeisturnedon,thatis,thecurrentflowsfromthe epoletothecpole.
2.Howtousetriode?
Theusagecharacteristicsofthetriode,thekeypointisthevoltage betweenthebpole(base)andtheelevel(emitter)ForPNP,theepole voltageisonly0.7Vhigherthantheblevel.Thereissmoothconduction betweenstagesThatis,thecontrollingendisbetweenbande,andthe controlledendisbetweeneandc.Similarly,theturn-onvoltageofthe NPNtransistoris0.7Vhigherthanthebpolethantheepole.Thisis theexplanationof"theconductionvoltagepassesalongthearrow,and thevoltageconducts".Let'stakeacommoncontrolLEDcircuitasan exampletoillustratetheworkingstateofcut-offandsaturation.As showninthefigurebelow,thebaseofthetriodeisconnectedtoanIO portofthemicrocontrollerthrougha10Kresistor,assumingitisP1, theemitterisdirectlyconnectedtothe5Vpowersupply,thecollector isconnectedtoanLED,anda1Kcurrentlimiterisconnectedinseries TheresistorisfinallyconnectedtothenegativeGNDofthepowersupply.
IfP1isgivenahighlevel1byourprogram,thenthebasebandtheemitter eareboth5V,thatistosay,therewillbeno0.7Vvoltagedropfrom etobAtthistime,theemitterandthecollectorwillalsoItwillnot beturnedon,sothecircuitisdisconnectedatthetriodewhenviewed verticallyIfthereisnocurrentpassingthrough,theLEDwillnotlight up.IftheprogramgivesP1alowlevelof0,thentheepoleisstill 5V,sothereisavoltagedifferencebetweeneandb,andthetransistors eandbarealsoturnedon,andthereisabout0.7Vbetweenthetransistor eandbThevoltagedrop,thenthereisavoltageof(5-0.7)Vacrossthe resistorR47.[Note]TheoutputhighleveloftheP1porthereis5V,and thehigh-leveloutputvoltageoftheIOportofdifferentsingle-chip microcomputersisdifferent.TheIOoutputofsomesingle-chip microcomputersis1.2V,whichrequirestriodeamplificationtodriveLEDs, etcWork.
Atthistime,theconnectionbetweeneandcwillalsobeturnedon,so theLEDitselfhasavoltagedropof2V,andthetriodeitselfhasavoltage dropofabout0.2Vbetweeneandc,whichweignore.Thentherewillbe avoltagedropofabout3VonR41,anditcanbecalculatedthatthecurrent ofthisbranchisabout3mA,whichcansuccessfullylightuptheLED.As mentionedearlier,thetriodehasthreestates:cut-off,amplification, andsaturationNeedlesstosay,thecut-offisaslongasthereisno conductionbetweeneandb.Wewantthistriodetobeinasaturatedstate, whichiswhatwecallswitchingcharacteristics,andaconditionmustbe met.Thetriodehasanamplificationfactorβ.Tobeinsaturation,the b-polecurrentmustbegreaterthanthecurrentvaluebetweeneandc dividedbyβ.Thisβcanbeconsideredtobeabout100forcommonlyused triodesThenwehavetocalculatetheresistancevalueofR47aboveJust nowwecalculatedthatthecurrentbetweeneandcis3mA,thentheminimum currentofthebpoleis3mAdividedby100equals30uA,about43Vvoltage willfallonthebaseresistor,thenthemaximumvalueofthebaseresistor is4.3V/30uA=143K.Aslongastheresistancevalueissmallerthanthis value,itisfine.Ofcourse,itcan’tbetoosmall.Toosmallwillcause theIOportcurrentofthemicrocontrollertoburnoutthetriodeorthe microcontroller.Themaximumtheoreticalvalueoftheinputcurrentof
theIOportis25mAIrecommendnotexceeding6mABycalculatingthe voltageandcurrent,theminimumresistancevaluecanbecalculated.
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