Lub zog hloov hluav taws xob ripple yog inevitable. Peb lub hom phiaj kawg yog kom txo cov zis ripple mus rau qib siab. Qhov kev daws teeb meem tseem ceeb tshaj plaws kom ua tiav lub hom phiaj no yog kom tsis txhob muaj cov ripples. Ua ntej tshaj plaws Thiab qhov ua rau.
Nrog rau qhov hloov ntawm SWITCH, qhov tam sim no nyob rau hauv inductance L kuj fluctuates nce thiab nqis ntawm tus nqi siv tau ntawm cov zis tam sim no. Yog li ntawd, tseem yuav muaj ib qho ripple uas yog tib zaus li Hloov ntawm qhov tso zis kawg. Feem ntau, cov ripples ntawm riber hais txog qhov no, uas muaj feem xyuam rau lub peev xwm ntawm cov zis capacitor thiab ESR. Qhov zaus ntawm qhov ripple no zoo ib yam li qhov hloov hluav taws xob, nrog rau ntau yam ntawm kaum mus rau pua pua kHz.
Tsis tas li ntawd, Hloov feem ntau siv bipolar transistors lossis MOSFETs. Tsis muaj teeb meem dab tsi, yuav muaj qhov nce thiab txo lub sijhawm thaum nws qhib thiab tuag. Lub sijhawm no, yuav tsis muaj suab nrov hauv Circuit Court uas zoo ib yam li lub sijhawm nce raws li Lub Sijhawm nce siab txo qis, lossis ob peb zaug, thiab feem ntau yog kaum ntawm MHz. Ib yam li ntawd, lub diode D yog nyob rau hauv thim rov qab. Qhov sib npaug Circuit Court yog cov kab hluav taws xob tiv thaiv thiab inductors, uas yuav ua rau muaj suab nrov, thiab lub suab nrov yog kaum ntawm MHz. Ob lub suab nrov no feem ntau hu ua high-frequency suab nrov, thiab lub amplitude feem ntau loj dua lub ripple.
Yog hais tias nws yog AC / DC converter, ntxiv rau saum toj no ob ripples (suab nrov), kuj muaj AC suab. Qhov zaus yog qhov zaus ntawm cov tswv yim AC fais fab mov, txog 50-60Hz. Kuj tseem muaj lub suab nrov co-mode, vim hais tias cov khoom siv hluav taws xob ntawm ntau lub zog hloov hluav taws xob siv lub plhaub ua lub tshuab hluav taws xob, uas ua rau muaj qhov sib npaug.
Kev ntsuas ntawm switching zog ripples
Cov kev xav tau yooj yim:
Coupling nrog oscilloscope AC
20MHz bandwidth txwv
Unplug hauv av xaim ntawm kev sojntsuam
1.AC coupling yog tshem tawm cov superposition DC voltage thiab tau txais qhov tseeb waveform.
2. Qhib 20MHz bandwidth txwv yog los tiv thaiv kev cuam tshuam ntawm lub suab nrov nrov thiab tiv thaiv qhov yuam kev. Vim hais tias lub amplitude ntawm high-frequency muaj pes tsawg leeg yog loj, nws yuav tsum tau muab tshem tawm thaum ntsuas.
3. Unplug hauv av clip ntawm oscilloscope sojntsuam, thiab siv cov av ntsuas ntsuas kom txo tau kev cuam tshuam. Ntau lub tuam tsev tsis muaj rings hauv av. Tab sis xav txog qhov no thaum txiav txim seb nws puas tsim nyog.
Lwm qhov taw qhia yog siv 50Ω davhlau ya nyob twg. Raws li cov ntaub ntawv ntawm oscilloscope, 50Ω module yog tshem tawm DC tivthaiv thiab ntsuas cov AC tivthaiv kom raug. Txawm li cas los xij, muaj ob peb oscilloscopes nrog cov kev soj ntsuam tshwj xeeb. Feem ntau, kev siv cov tshuaj ntsuam xyuas los ntawm 100kΩ mus rau 10MΩ yog siv, uas yog ib ntus tsis meej.
Cov saum toj no yog cov kev ceev faj yooj yim thaum ntsuas qhov hloov ripple. Yog hais tias lub oscilloscope sojntsuam tsis ncaj qha mus rau cov zis taw tes, nws yuav tsum tau ntsuas los ntawm twisted kab los yog 50Ω coaxial cables.
Thaum ntsuas lub suab nrov nrov, tag nrho cov qhab ntawm oscilloscope feem ntau yog ntau pua mega rau GHz. Lwm tus kuj zoo ib yam li cov saum toj no. Tej zaum cov tuam txhab sib txawv muaj cov kev sim sib txawv. Hauv qhov kev ntsuam xyuas zaum kawg, koj yuav tsum paub koj cov txiaj ntsig kev xeem.
Hais txog oscilloscope:
Qee cov oscilloscope digital tsis tuaj yeem ntsuas ripples kom raug vim muaj kev cuam tshuam thiab cia qhov tob. Lub sijhawm no, lub oscilloscope yuav tsum tau hloov. Qee lub sij hawm txawm hais tias qhov qub simulation oscilloscope bandwidth tsuas yog kaum ntawm mega, qhov kev ua tau zoo dua li cov oscilloscope digital.
Inhibition ntawm switching zog ripples
Rau kev hloov ripples, theoretically thiab yeej muaj. Muaj peb txoj hauv kev los txwv lossis txo nws:
1. Ua kom cov inductance thiab tso zis capacitor lim
Raws li cov qauv ntawm cov khoom siv hluav taws xob hloov pauv, qhov hloov pauv tam sim no loj thiab inductance tus nqi ntawm cov inductive inductance ua inversely proportional, thiab cov zis ripples thiab output capacitors yog inversely proportional. Yog li ntawd, nce hluav taws xob thiab tso zis capacitor tuaj yeem txo ripples.
Daim duab saum toj no yog qhov tam sim no waveform nyob rau hauv lub switching fais fab mov inductor L. Nws ripple tam sim no △ kuv tuaj yeem xam los ntawm cov qauv hauv qab no:
Nws tuaj yeem pom tias nce L tus nqi lossis nce qhov zaus hloov pauv tuaj yeem txo qhov kev hloov pauv tam sim no hauv inductance.
Ib yam li ntawd, kev sib raug zoo ntawm cov zis ripples thiab cov zis capacitors: VRIPPLE = IMAX/(CO × F). Nws tuaj yeem pom tau tias nce qhov tso zis capacitor tus nqi tuaj yeem txo qhov ripple.
Txoj kev niaj zaus yog siv txhuas electrolytic capacitors rau cov zis capacitance kom ua tiav lub hom phiaj ntawm lub peev xwm loj. Txawm li cas los xij, electrolytic capacitors tsis muaj txiaj ntsig zoo hauv kev tawm suab nrov nrov, thiab ESR yog qhov loj, yog li nws yuav txuas lub ceramic capacitor ntawm nws los ua kom tsis muaj txhuas electrolytic capacitor.
Nyob rau tib lub sij hawm, thaum lub hwj chim mov ua hauj lwm, qhov voltage VIN ntawm lub input davhlau ya nyob twg yog tsis hloov, tab sis tam sim no hloov nrog lub hloov. Lub sijhawm no, cov khoom siv hluav taws xob input tsis muab lub qhov dej tam sim no, feem ntau nyob ze ntawm qhov tam sim no input davhlau ya nyob twg (siv hom puck raws li piv txwv, yog nyob ze Hloov), thiab txuas lub capacitance los muab tam sim no.
Tom qab siv qhov kev ntsuas no, Buck hloov hluav taws xob yog qhia hauv daim duab hauv qab no:
Txoj hauv kev saum toj no tsuas yog txo qis ripples. Vim lub ntim txwv, qhov inductance yuav tsis loj heev; cov zis capacitor nce mus rau ib qho degree, thiab tsis muaj kev cuam tshuam rau kev txo cov ripples; qhov nce ntawm qhov hloov zaus yuav ua rau qhov hloov pauv poob. Yog li thaum cov kev cai nruj heev, txoj kev no tsis zoo heev.
Rau cov hauv paus ntsiab lus ntawm kev hloov hluav taws xob, koj tuaj yeem xa mus rau ntau hom kev hloov hluav taws xob tsim cov ntawv qhia.
2. Ob-theem filtering yog ntxiv thawj-theem LC lim
Cov nyhuv inhibitory ntawm LC lim ntawm lub suab nrov ripple yog qhov pom tseeb. Raws li qhov ripple zaus yuav tsum tau muab tshem tawm, xaiv qhov tsim nyog inductor capacitor los tsim cov lim lim. Feem ntau, nws tuaj yeem txo cov ripples zoo. Hauv qhov no, koj yuav tsum xav txog qhov piv txwv ntawm qhov tawm tswv yim voltage. (Raws li qhia hauv qab no)
Cov ntsiab lus piv txwv raug xaiv ua ntej LC lim (PA), thiab cov zis hluav taws xob yuav raug txo. Vim tias ib qho inductance muaj DC tsis kam, thaum muaj qhov tso tawm tam sim no, yuav muaj qhov poob qis hauv qhov inductance, uas ua rau txo qis hauv qhov tso zis hluav taws xob ntawm lub zog hluav taws xob. Thiab qhov no voltage poob hloov nrog cov zis tam sim no.
Cov ntsiab lus piv txwv raug xaiv tom qab LC lim (PB), kom cov zis hluav taws xob yog qhov hluav taws xob peb xav tau. Txawm li cas los xij, ib qho inductance thiab lub capacitor tau nkag rau hauv lub zog hluav taws xob, uas yuav ua rau lub cev tsis ruaj khov.
3. Tom qab qhov tso zis ntawm lub zog hloov pauv, txuas LDO lim
Qhov no yog txoj hauv kev zoo tshaj plaws los txo cov ripples thiab suab nrov. Cov zis hluav taws xob tsis tu ncua thiab tsis tas yuav hloov pauv qhov kev tawm tswv yim thawj zaug, tab sis nws kuj yog tus nqi tshaj plaws - ua haujlwm zoo thiab siv lub zog siab tshaj plaws.
Txhua LDO muaj qhov taw qhia: suab nrov txo qis. Nws yog qhov nkhaus zaus-DB, raws li qhia hauv daim duab hauv qab no yog qhov nkhaus ntawm LT3024 LT3024.
Tom qab LDO, qhov hloov pauv ripple feem ntau qis dua 10mV. Cov duab hauv qab no yog qhov sib piv ntawm ripples ua ntej thiab tom qab LDO:
Piv nrog rau qhov nkhaus ntawm daim duab saum toj no thiab lub waveform ntawm sab laug, nws tuaj yeem pom tias cov nyhuv inhibitory ntawm LDO zoo heev rau kev hloov ripples ntawm ntau pua KHz. Tab sis nyob rau hauv ntau zaus, cov nyhuv ntawm LDO tsis yog qhov zoo tagnrho.
Txo ripples. PCB thaiv kev hloov hluav taws xob hloov pauv tseem ceeb heev. Rau lub suab nrov nrov, vim yog qhov loj ntawm qhov ntau zaus, txawm hais tias tom qab-stage filtering muaj qee qhov cuam tshuam, cov nyhuv tsis pom tseeb. Muaj kev kawm tshwj xeeb hauv qhov no. Txoj hauv kev yooj yim yog nyob ntawm diode thiab capacitance C lossis RC, lossis txuas cov inductance hauv koob.
Daim duab saum toj no yog qhov sib npaug ntawm qhov tseeb diode. Thaum lub diode yog high-speed, parasitic tsis yuav tsum tau xav txog. Thaum lub sij hawm rov qab los ntawm lub diode, qhov sib npaug inductance thiab sib npaug capacitance tau dhau los ua RC oscillator, tsim kom muaj ntau zaus oscillation. Txhawm rau txhawm rau txhim kho qhov siab tshaj plaws oscillation, nws yog ib qho tsim nyog los txuas kev sib txuas c los yog rc ntas yeej ntawm ob qho kawg ntawm Diode. Qhov tsis kam yog feem ntau 10Ω-100 ω, thiab lub peev xwm yog 4.7PF-2.2NF.
Lub capacitance C lossis RC ntawm diode C lossis RC tuaj yeem txiav txim siab los ntawm kev sim rov ua dua. Yog tias nws tsis raug xaiv kom raug, nws yuav ua rau oscillation hnyav dua.
Lub sij hawm xa tuaj: Plaub Hlis-08-2023
