Nyob rau hauv tus txheej txheem ntawm kev tsim ib tug switching fais fab mov, lub lim capacitor yuav tsum tau xaiv kom raug?
Lub lim capacitor plays lub luag haujlwm tseem ceeb hauv kev hloov hluav taws xob. Yuav ua li cas xaiv lub lim capacitor kom raug, tshwj xeeb tshaj yog kev xaiv ntawm cov zis lim capacitor yog ib qho teeb meem uas txhua tus engineer thiab cov kws tshaj lij muaj kev txhawj xeeb heev. Peb tuaj yeem pom ntau yam capacitors ntawm lub zog lim hluav taws xob, 100uF, 10uF, 100nF, 10nF nrog cov nqi sib txawv, yog li cov kev ntsuas no tau txiav txim siab li cas? Tsis txhob qhia kuv tias kuv tau theej lwm tus tus schematic daim duab, huh, huh.
Rau cov electrolytic capacitors siv nyob rau hauv 50Hz fais fab zaus circuits, lub pulsating voltage zaus tsuas yog 100Hz, thiab lub sij hawm them thiab tawm yog nyob rau hauv qhov kev txiav txim ntawm milliseconds. Yuav kom tau txais ib qho me me pulsation coefficient, qhov yuav tsum tau muaj peev xwm yog siab li ntau pua txhiab μF. Yog li ntawd, lub hom phiaj ntawm qhov zoo tib yam tsawg zaus txhuas electrolytic capacitors yog ua kom lub capacitance. Lub ntsiab parameter ntawm pros thiab cons. Txawm li cas los xij, cov zis lim electrolytic capacitor nyob rau hauv cov khoom siv hluav taws xob hloov hluav taws xob muaj qhov hluav taws xob sawtooth yoj voltage ntau npaum li kaum tawm kHz, lossis txawm kaum ntawm MHz. Lub sij hawm no, lub capacitance tsis yog lub ntsiab qhia. Tus qauv ntsuas qhov zoo ntawm high-frequency aluminium electrolytic capacitors yog "impedance-" zaus" cov yam ntxwv, nws yuav tsum muaj qhov sib npaug qis dua nyob rau hauv kev khiav hauj lwm zaus ntawm kev hloov hluav taws xob, thiab tib lub sijhawm muaj kev lim dej zoo. cuam tshuam rau lub high-frequency spikes generated thaum lub semiconductor ntaus ntawv ua hauj lwm.
Ordinary low-frequency electrolytic capacitors pib qhia inductivity nyob ib ncig ntawm 10kHz, uas tsis tuaj yeem ua tau raws li qhov yuav tsum tau muaj ntawm kev hloov khoom siv hluav taws xob. Lub high-frequency txhuas electrolytic capacitor nplooj siab rau lub switching fais fab mov muaj plaub terminals. Ob qhov kawg ntawm daim ntawv zoo txhuas yog feem ntau kos tawm raws li qhov zoo electrode ntawm lub capacitor, thiab ob qhov kawg ntawm daim ntawv tsis zoo txhuas kuj raug cuam tshuam raws li qhov tsis zoo electrode. Tam sim no ntws los ntawm ib lub davhlau ya nyob twg zoo ntawm plaub lub davhlau ya nyob twg capacitor, dhau los ntawm sab hauv ntawm lub capacitor, thiab tom qab ntawd ntws los ntawm lwm qhov zoo tshaj plaws mus rau lub load; Tam sim no rov qab los ntawm lub load kuj ntws los ntawm ib qho tsis zoo davhlau ya nyob twg ntawm lub capacitor, thiab ces ntws los ntawm lwm yam tsis zoo davhlau ya nyob twg mus rau qhov tsis zoo davhlau ya nyob twg ntawm lub hwj chim mov.
Txij li thaum plaub lub davhlau ya nyob twg capacitor muaj cov yam ntxwv siab zaus, nws muab cov txiaj ntsig zoo heev rau kev txo cov pulsating tivthaiv ntawm qhov hluav taws xob thiab txo qis lub suab nrov ntawm kev hloov pauv. High-frequency aluminium electrolytic capacitors kuj muaj ntau daim ntawv, uas yog, cov ntawv txhuas txhuas tau muab faib ua ob peb ntu luv, thiab ntau cov hlau lead yog txuas nrog rau tib lub sijhawm kom txo cov impedance tivthaiv hauv capacitive reactance. Thiab kev siv cov ntaub ntawv uas tsis tshua muaj zog raws li cov hlau lead-out terminals txhim kho lub peev xwm ntawm lub capacitor kom tiv taus cov dej loj.
Rau cov hluav taws xob digital kom ua haujlwm ruaj khov thiab ntseeg tau, cov khoom siv hluav taws xob yuav tsum "huv", thiab lub zog ntxiv yuav tsum tau raws sijhawm, uas yog, lim thiab decoupling yuav tsum zoo. Dab tsi yog filtering thiab decoupling, yooj yim muab, nws yog khaws cia lub zog thaum lub nti tsis xav tau tam sim no, thiab kuv tuaj yeem ntxiv zog rau lub sijhawm thaum koj xav tau tam sim no. Tsis txhob qhia kuv tias lub luag haujlwm no tsis yog rau DCDC thiab LDO? Yog lawm, ntawm qhov tsawg zaus lawv tuaj yeem tswj tau nws, tab sis kev kub ceev digital systems txawv.
Cia peb saib ntawm lub capacitor ua ntej. Lub luag haujlwm ntawm lub capacitor tsuas yog khaws cov nqi xwb. Peb txhua tus paub tias capacitor filtering yuav tsum tau ntxiv rau lub hwj chim mov, thiab ib tug {{0}}}.1uF capacitor yuav tsum tau muab tso rau ntawm lub hwj chim tus pin ntawm txhua nti rau decoupling, thiab lwm yam. Vim li cas kuv thiaj li pom tias lub capacitor ib sab ntawm lub hwj chim tus pin ntawm ib co board chips yog 0.1uF los yog 0.01uF Yog, yog dab tsi? Txhawm rau kom nkag siab qhov tseeb no, peb yuav tsum nkag siab txog cov yam ntxwv tiag tiag ntawm capacitor. Ib qho zoo tagnrho capacitor yog ib qho chaw cia khoom xwb, uas yog C. Txawm li cas los xij, qhov tseeb tsim capacitor tsis yooj yim li. Thaum txheeb xyuas qhov kev ncaj ncees ntawm cov khoom siv hluav taws xob, cov qauv siv capacitor feem ntau pom hauv daim duab hauv qab no.
Nyob rau hauv daim duab, ESR yog qhov sib npaug sib npaug ntawm lub capacitor, ESL yog qhov sib npaug inductance ntawm lub capacitor, thiab C yog qhov zoo tagnrho capacitor. ESR thiab ESL yog txiav txim los ntawm cov txheej txheem tsim khoom thiab cov khoom siv ntawm lub capacitor thiab tsis tuaj yeem raug tshem tawm. Ob yam no cuam tshuam li cas rau hauv Circuit Court. ESR cuam tshuam lub ripple ntawm lub hwj chim mov, thiab ESL cuam tshuam rau lub lim zaus yam ntxwv ntawm lub capacitor.
Peb paub tias lub capacitive reactance Zc=1/ωC ntawm lub capacitor, inductive reactance Zl=ωL ntawm inductor, (ω=2πf), thiab qhov nyuaj impedance ntawm lub capacitor tiag yog Z=ESR plus jωL-1/jωC=ESR plus j2πf L-1/j2πf c. Nws tuaj yeem pom tau tias thaum qhov zaus qis heev, lub peev xwm ua haujlwm tau ua lub luag haujlwm, thiab thaum qhov zaus siab mus rau ib theem, lub luag haujlwm ntawm inductance tsis tuaj yeem tsis quav ntsej, thiab thaum qhov zaus siab dua, qhov inductance yuav ua si. coj lub luag haujlwm. Lub capacitor poob nws cov nyhuv lim dej. Yog li nco ntsoov, thaum qhov zaus siab, lub capacitor tsis yog lub capacitor xwb.
Raws li tau hais los saum no, qhov sib npaug series inductance ntawm lub capacitor yog txiav txim siab los ntawm cov txheej txheem tsim khoom thiab cov khoom siv ntawm lub capacitor. Lub ESL ntawm qhov tseeb nti ceramic capacitor ranges ntawm ob peb feem kaum ntawm nH mus rau ntau nH, thiab cov pob me me, qhov me dua ESL.
Los ntawm lub lim nkhaus ntawm lub capacitor saum toj no, peb kuj tuaj yeem pom tias nws tsis tiaj tus, nws zoo li 'V', uas yog hais tias, nws muaj zaus xaiv cov yam ntxwv, thiab peb cia siab tias nws yog tiaj li sai tau ( pre-stage board-level filtering), Thiab qee zaum koj xav kom nws ua kom ntse li sai tau (filtering lossis notching). Dab tsi cuam tshuam rau tus yam ntxwv no yog qhov zoo tshaj plaws Q ntawm lub capacitor, Q=1/ωCESR, qhov loj dua ESR, qhov me Q, thiab qhov nkhaus nkhaus. Ntawm qhov tsis sib xws, qhov me dua ESR, qhov loj dua Q, thiab qhov nkhaus nkhaus. Feem ntau, tantalum capacitors thiab txhuas electrolytics muaj qhov me me ESL, tab sis ESR loj, yog li tantalum capacitors thiab txhuas electrolytics muaj ntau zaus siv tau, uas yog qhov tsim nyog rau lub rooj tsav xwm pem hauv ntej kawg. Qhov ntawd yog hais tias, lub peev xwm loj tantalum capacitor feem ntau yog siv rau kev lim dej ntawm DCDC lossis LDO. Thiab muab qee qhov 10uF thiab 0.1uF capacitors ze ntawm lub nti rau kev txiav, ceramic capacitors muaj ESR qis heev.
