MOSFET的原理特性作用及应用.ppt

2020 1 17 1 MOSFET的原理特性作用及應用 2020 1 17 2 MOSFET的全稱 MOSFET全稱 MetalOxideSemiconductortypeFieldEffectTransistor金屬氧化物半導體場效應晶體管又叫絕緣柵場效應管 是指其柵極處於不導電 絕緣 狀態 輸入阻抗高 2020 1 17 3 TheStructureofMOSFET DEPLETION 耗盡 用盡BULK 塊SUBSTRATE 底板HEAVILY 濃烈的DOPE 塗層 2020 1 17 4 TheStructureofMOSFET cont Epitaxial 取向附生的 2020 1 17 5 TheStructureofMOSFET cont 2020 1 17 6 TheStructureofMOSFET cont 2020 1 17 7 MOSFET的工作原理 MOSFET就是利用柵極電壓的大小 來改變半導體表面感生電荷的大小 從而控制漏極電流的大小 2020 1 17 8 MOSFET的分類 符號 優點 缺點 作用 1 分類增強型和耗盡型兩種增強型是指vgs 0時 沒有導電溝道 id 0 黨vgs vt時 才有導電溝道 才有id 耗盡型是指vgs 0時 有導電溝道 id不等於0增強型又分N型MOSFET和P型MOSFET兩種2 符號NMOSFETPMOSFET3 優缺點a 輸入阻抗高b 動作快 工作蘋率高 c 具正溫度係數 並聯可自動均流d 耐壓高e 導通電流難做大 4 作用主要是作為開關元件 2020 1 17 9 TheSpecificationofMOSFET 2020 1 17 10 TheSpecificationofMOSFET cont 2020 1 17 11 ThegatedrivermustsupplyI1toC1andI2toC2 BecauseoftheMillereffect I2maybegraterthanI1eventhoughC1maybe10timesaslargerC2 Assume Vgs 10V Vdc in 12VC1 1800pF C2 150pF Tr 50nS 2020 1 17 12 Shootthrough GateBounce CapacitivecouplinghappensespeciallyatQgdperiod Tostopgatebounce 2020 1 17 13 TheSpecificationofMOSFET cont 2020 1 17 14 TheSpecificationofMOSFET cont Ton Toff 2020 1 17 15 OutputCharacteristicCurveofMOSFET cont OutputCharacteristicCurve 2020 1 17 16 TransferCharacteristicCurveofMOSFET cont TransferCharacteristicCurve 2020 1 17 17 GateChargeDiagramandCrossover 2020 1 17 18 EquivalentcircuitsoftheMOSFETturn on equivalentcircuitofperiodt3 t4 equivalentcircuitofperiodt0 t1 equivalentcircuitofperiodt1 t2 equivalentcircuitofperiodt2 t3 2020 1 17 19 工作區ofMOSFET VGS VT 0 VDS VGS VT夾止區 飽和區 定電流區 工作區 信號放大區 2020 1 17 20 工作區ofMOSFET cont VGS VT 0 VDS VGS VT線性區 未飽和區 歐姆區 2020 1 17 21 工作區ofMOSFET cont Ohmicregion Constantresistanceregion Ifdrain to sourcevoltageiszero thedraincurrentalsobecomeszeroregardlessofgate to sourcevoltage ThisregionisattheleftsideofVGS VGS th VDSboundaryline VGS VGS th VDS 0 andinthisregion evenifthedraincurrentisverylarge thepowerdissipationcouldbemaintainedbyminimizingtheVDS on Saturationregion Constantcurrentregion ItisattherightsideofVGS VGS th VDSboundaryline andinthisregion thedraincurrentdiffersbythegate to sourcevoltage notbythedrain to sourcevoltage Here thedraincurrentiscalledsaturated Cut offregion Itiscalledcut offregion whenthegate to sourcevoltageislowerthanVGS th thresholdvoltage 2020 1 17 22 MOSFETpowerlossforDC DCConversion ThereareseveralpossiblepowerlosssourcesinaMOSFET1 PS SwitchingTransitionLosses2 PG GateDriveLosses3 PC ConductionLosses4 PL DraintoSourceLeakageCurrentLosses5 PD InternalDiodeLosses 2020 1 17 23 MOSFETpowerlossforDC DCConversion cont 2020 1 17 24 MOSFETpowerlossforDC DCConversion cont 2020 1 17 25 MOSFETpowerlossforDC DCConversion cont 2020 1 17 26 MOSFETpowerlossforDC DCConversion cont 2020 1 17 27 MOSFETpowerlossforDC DCConversion cont 2020 1 17 28 MOSFETSelectionforLoadSwitch 2020 1 17 29 MOSFETSelectionforLoadSwitch cont 2020 1 17 30 MOSFETSelectionforLoadSwitch cont 2020 1 17 31 MOSFETSelectionforLoadSwitch cont 2020 1 17 32 BasicDC DCbuckconverterarchitecture SGND Vcc Rin Vcc Pvcc LPCB1 LOUT COUT LPCB2 RISEN PGND SGND Driver PWMControllor SGND VID0VID1VID2VID3VID4 ISEN PWM VSEN EN PGOOD COMP FB 2020 1 17 33 1 H Sturnoff L Sturnon 0V 0V Vsync die 0V 0V Iout constant 2020 1 17 34 t1 t3 VGS plateau VGS th 2020 1 17 35 2 H Sturnon L Sturnoff Qgs2period lowdi dt Qgd Qgs2 2020 1 17 36 2 H Sturnon L Sturnoff Qgs2period lowdi dt Lowdi dt 2020 1 17 37 2 H Sturnon L Sturnoff Qgs2period lowdi dt VLpcb1 VLs cont VLs sync VLpcb2 Iout constant Vsnode Vsync die Id contincreasing Id syncdecreasing Vsnode Vin VLpcb1 VLS cont Vcont die Vcont die 2020 1 17 38 3 H Sturnon L Sturnoff Qgdperiod highdi dt Qgs2 Qgd 2020 1 17 39 3 H Sturnon L Sturnoff Qgdperiod highdi dt highdi dt 2020 1 17 40 3 H Sturnon L Sturnoff Qgdperiod highdi dt VLpcb1 VLs cont VLs sync VLpcb2 Iout constant Vsync die Id synckeepdecreasing AlmostzerobytheendofQgd Vsnode Vin VLpcb1 Vcont die VLS cont Vsnode Vin IfVin 12VVsnode 16VpkLpcb1 Lpcb2Ls cont Ls sync Vsync die 12V 4V 4V 20V Vcont die 2020 1 17 41 Vds 0 Isd Id syncthroughbodydiodealmostconstant DuringQgs2 VLS sync Vcpcb2 Id decreasing H S OFFL S ON H S OFFL S OFF H S ONL S OFFQgs2 Qgd H S ONL S OFF Id rampdown Idrampup Id decreasing 21 0 Ids Vds DuetoQrr Qoss Vds H S L S Vsd 2020 1 17 42 Considerationfactorofmosfetapplication 1 Vdsfornotebook atleast30v2 IdsIds 2 3 Ipeak3 Vgs 20vduetospikeect Factor Vgsselectionshouldkeepmargin ifgatetosourcebreakdown mosfetwilldamagefor ever4 ForH smosfetinBUCKcircuit mainlossisswitchingloss ShouldselectmosfetwithsmallQgdandCissforL SmosfetinBUCKcircuit mainlossisconductionloss shouldselectsmallRds on mosfet 2020 1 17 43 HowtoCalculateTj 2020 1 17 44 HowtoCalculateTj cont 2020 1 17 4