Mosfet功耗介绍与计算

MOSFET功耗種類介紹與計算Preparedby:StevenHsuMOSFET功耗通常在一些資訊中只提到導通損失和開關損失，在上下橋接或同步整流應用實務上還包含下列幾項損失，在功耗上的貢獻，在不同的應用拓樸會有不同程度的貢獻，以下我們將進一步來探討。•1.導通損失Conductionloss•2.開關損失Switchingloss•3.柵極驅動損失Gatedriveloss•4.体二極管導通損失Bodydiodeconductionloss•5.体二極管逆向恢復損失Diodereverse-recoveryloss•6.輸出電容損失OutputcapacitancelossMOSFET功耗種類介紹1.導通損失Conductionloss:MOSFET控制導通狀態下，洩極電流流經MOSFET洩、源及所產生之功耗損失稱之，在圖1MOSFET動作波形時序圖中，為在t4~t6週期時間所產生的功耗，其功耗等於:Pcond=Irms²xRds(on)。MOSFET功耗種類介紹圖1MOSFET動作波形時序圖MOSFET功耗種類介紹2.開關損失Switchingloss:MOSFET控制開通與關斷轉態下，所產生之開關切換功耗損失稱之，在圖1MOSFET動作波形時序圖中，為在t2~t3與t7~t8週期時間所產生的功耗。其中t2~t3週期為開通時之開關損失，t7~t8週期則為關斷之開關損失。值得注意的是有些時候開關損失會大於導通損失，所以才會發展出零電壓、零電流等柔性切換拓樸產生，來降低開關切換動作時所帶來之功耗損失。其功耗在不同拓樸會有些許變化，以下為buck同步整流範例，其功耗等於:*t2+t3=t7+t8MOSFET功耗種類介紹3.柵極驅動損失Gatedriveloss:MOSFET控制開通必須將柵極充電至最高驅動電壓，此時向柵極充滿電荷所產生之驅動功耗損失稱之，在圖1MOSFET動作波形時序圖中下方，為在t1~t4顯示柵極各周期電荷量，控制開通時從t1開始充電，直至t4柵極充滿電荷，關斷時t7開始放電，直至t9完全放電，以下為buck同步整流範例，其功耗等於:Pgate(HS)=Qg(HS)xVdriverxfswPgate(LS)=Qg(HS)xVdriverxfswMOSFET功耗種類介紹4.体二極管導通損失Bodydiodeconductionloss:MOSFET在柵極未轉態前或防止開關同時導通而提前關閉柵極電壓時間(deadtime)，而源極電流流經MOSFET源、洩間之寄生体二極管及所產生之導通功耗損失稱之，在圖2MOSFET動作波形時序圖中，為在Td週期時間所產生的功耗，其功耗等於:Pdiode=IsdxVdxtdxfsw。圖2MOSFET動作波形時序圖MOSFET功耗種類介紹5.体二極管逆向恢復損失Diodereverse-recoveryloss:MOSFET控制關斷轉態下，MOS開關之体二極管如PN介面二極館特性一樣會有延遲關斷現象所產生之体二極管逆向恢復功耗損失稱之，在下圖，以下為buck同步整流範例，其功耗等於:圖3diodereverse-recoverywaveformMOSFET功耗種類介紹6.輸出電容損失Outputcapacitanceloss:MOSFET在關斷時其洩、源極間之寄生輸出電容會被充電，此時向寄生輸出電容充滿電荷所產生之功耗損失稱之，以下為flyback同步整流範例，其功耗等於:Pcoss_pwm=1/2xCoss_pwmxVds_pwm²xfswPcoss_sr=1/2xCoss_srxVds_sr²xfswMOSFET功耗計算範例PWMMOSParameterDataUnitOutputvoltage:Vo5VOutputcurrent:Io2ADutycycle:D45%GateThresholdVoltage:VTH3VPRIMOSRMScurrent0.36AForwardTransconductance65STotalGateCharg:QG105nCGate-SourceCharg:QGS24nCGate-DrainCharg:QGD31nCReverseRecoveryCharge:Qrr46nCInputCapacitanc:CISS(typ)1200pFOutputCapacitance:COSS(typ)100pFReverseTransferCapacitance:Crss10pFTurnonresistance:RDS(ON)2ΩGateResistance:Rg(typ)3ΩForwardOnVoltage:VSD1VDeadtime:DT100nSDrivevoltage:VDriver12VVGSforQGtestcondition10VExternalGateresitence200ΩDriveroutputresitence10ΩInputvoltage:VIN95VSwitchingfrrequency:fsw75kHZQGforVdriver126nCReflectvoltageVr76VPrimaryIp0.55ASRMOSParameterDataUnitGateThresholdVoltage:VTH3VSRMOSRMScurrent2.3AForwardTransconductance65STotalGateCharg:QG85nCGate-SourceCharg:QGS24nCGate-DrainCharg:QGD31nCReverseRecoveryCharge:Qrr46nCInputCapacitanc:CISS(typ)5000pFOutputCapacitance:COSS(typ)2550pFReverseTransferCapacitance:Crss35pFTurnonresistance:RDS(ON)16mΩGateResistance:Rg(typ)3ΩForwardOnVoltage:VSD1VDeadtime:DT100nSDrivevoltage:VDriver12VVGSforQGtestcondition10VExternalGateresitence10ΩDriveroutputresitence10ΩSRMOSvoltage:VDS50VSwitchingfrrequency:fsw75kHZQGforVdriver102.00nCFlybackMOSFET參數表MOSFET功耗計算範例FLYBACKPRIMOSFETLOSSCALCULATIONPWMMOSFET10%load20%load30%load40%load50%load60%load70%load80%laod90%load100%loadConductionloss(W)0.0030.0100.0230.0410.0650.0930.1270.1660.2100.259Switchingloss(W)0.0040.0160.0240.0320.0400.0480.0560.0640.0720.080Gatedriveloss(W)0.0230.0570.0910.1130.1130.1130.1130.1130.1130.113Bodydiodeloss(W)0.0000.0000.0000.0000.0000.0000.0000.0000.0000.000Diodereverse-recoveryloss(W)0.0000.0000.0000.0000.0000.0000.0000.0000.0000.000Outputcapacitanceloss(W)0.0070.0170.0270.0340.0340.0340.0340.0340.0340.034TotallossforPWM(W)0.0360.1000.1650.2210.2520.2890.3300.3770.4290.487Outputpower(W)1.02.03.04.05.06.07.08.09.010.0Efficiency(%)78.9873.7874.4576.1678.2880.1181.3382.1582.6883.01SRMOSFET10%load20%load30%load40%load50%load60%load70%load80%laod90%load100%loadConductionloss(W)0.0010.0030.0080.0140.0210.0300.0410.0540.0690.085Switchingloss(W)0.0000.0000.0000.0000.0000.0000.0000.0000.0000.000Gatedriveloss(W)0.0180.0460.0730.0920.0920.0920.0920.0920.0920.092Bodydiodeloss(W)0.0130.0260.0390.0520.0650.0780.0910.1040.1170.130Diodereverse-recoveryloss(W)0.0040.0100.0160.0200.0200.0200.0200.0200.0200.020Outputcapacitanceloss(W)0.0100.0600.1530.1910.2390.2390.2390.2390.2390.239Totalloss(W)0.0460.1450.2890.3690.4370.4590.4830.5090.5360.565Outputpower(W)1.02.03.04.05.06.07.08.09.010.0MOSFET功耗計算範例Excel計算工具參考: