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1MOSFET在感性负载下的开关损耗公式张兴柱博士2015年6月2一:分析MOSFET开关过程的原理图3)(tvgsDGS)(tid)(tiLoV)(tvd)(tis)(tvdsgV1:电流负载下的等效电路下面的分析中假定:---电感电流在开关过程中保持不变;---MOSFET要考虑其寄生参数;---二极管分两种情况(无反向恢复和有反向恢复)。42:分析用MOSFET的简化等效电路)(tvgsDGSgsCdsCgdC)(tid)(tiLoV)(tvd)(tis)(tvds)(tvdrive1ggR2ggRgV)(tidsgdossdsCCCgdissgsCCCrssgdCC为了简化分析,先对进行分析然后再从它的分析结果,来对比分析获得时的结果0dsC0dsC5二:MOSFET的开关过程原理及分析0dsC(二极管无反向恢复)6--在t0前,MOSFET工作于截止状态,t0时,MOSFET被驱动开通;开通过程的轨迹图开通过程的波形图[t0-t1]区间:图中红色Phase1这点轨迹。MOSFET的GS电压经Vcc对Cgs充电而上升,在t1时刻,到达维持电压Vgs(th),MOSFET开始导电。)(tvgsDGSgsCgdC)(tid)(tiLoV)(tvd)(tis)(tvdsccV1ggR2ggRgV)(tids[t0-t1]区间的等效电路)1ln()(1011ccthgsgsggVVCRttt0)()(titidssopeakdsdsVVtv)1()(dsVfsLthgsgsGIVV1)(1dsI1LI)(thgsV1ont2ont)1(peakdsVccgsVVPhase1Phase2Phase4Phase3ccV)(tvgs)(tis)(tvds)1(peakdsV2ont1ont)(thgsVontt1LIccV)(tvdrive)(thgsV)(tids1LI1gsV0t4t1t2t3t1:MOSFET的开通过程原理推导见下页7[t0-t1]区间:ccgsgsgsggVVdtdVCR10)(0tVgs)1()(10gsggCRttccgseVtV)(1)1()(101thgsCRttccgsVeVtVgsgg)1ln()(111ccthgsgsggoVVCRtttccV)(tvgs)(tis)(tvds)1(peakdsV2ont1ont)(thgsVontt1LIccV)(tvdrive)(thgsV)(tids1LI1gsV0t4t1t2t3t)(tvgsDGSgsCgdC)(tid)(tiLoV)(tvd)(tis)(tvdsccV1ggR2ggRgV)(tids方程初始值解t1时刻该间隔是MOSFET的延迟开通间隔。8开通过程的轨迹图开通过程的波形图[t1-t2]区间:图中黄色Phase2这段轨迹。)(tvgsDGSgsCgdC)(tid)(tiLoV)(tvd)(tis)(tvds1ggR2ggRgV)(tidsccV])([)()(thgsgsfsdsVtvGti[t1-t2]区间的等效电路opeakdsdsVVtv)1()(dsVfsLthgsgsGIVV1)(1dsI1LI)(thgsV1ont2ont)1(peakdsVccgsVVPhase1Phase2Phase4Phase3ccV)(tvgs)(tis)(tvds)1(peakdsV2ont1ont)(thgsVontt1LIccV)(tvdrive)(thgsV)(tids1LI1gsV0t4t1t2t3t1)(11lngsccthgsccgsggonVVVVCRt另外:])([)()(thgsgsfsdsVtvGti当DS电流增加到,该间隔结束,二极管关断。此时:fsLthgsgsgsGIVVtv1)(1)(1LIMOSFET的DS电流因Vgs的增加而增加,如下式:从上式,可将DS看作是一个受控电流源。推导见下页9[t1-t2]区间:ccV)(tvgs)(tis)(tvds)1(peakdsV2ont1ont)(thgsVontt1LIccV)(tvdrive)(thgsV)(tids1LI1gsV0t4t1t2t3tccgsgsgsggVVdtdVCR10)(0tVgs)1()(10gsggCRttccgseVtV12102121)(tttttttttoon其中:)1ln()(111ccthgsgsggoVVCRttt)1ln(112ccgsgsggVVCRt11)(2)1()(102gsfsLthgsCRttccgsVGIVeVtVgsgg所以:1)(1121lngsccthgsccgsggonVVVVCRttt)(tvgsDGSgsCgdC)(tid)(tiLoV)(tvd)(tis)(tvds1ggR2ggRgV)(tidsccV])([)()(thgsgsfsdsVtvGti方程初始值解t2时刻该间隔中DS电压保持不变,MOSFET的DS电流则可近似看成线性上升,间隔结束时刚好上升到外部电流。10开通过程的轨迹图开通过程的波形图DGSgsCgdC)(tid)(tiLoV)(tvd)(tis)(tvds1ggR2ggRgV)(tids1LI1gsVccV11gggsccRVV[t2-t3]区间的等效电路)1(211)()(peakdsgdgggsccdsVttCRVVtvdsVfsLthgsgsGIVV1)(1dsI1LI)(thgsV1ont2ont)1(peakdsVccgsVVPhase1Phase2Phase4Phase3ccV)(tvgs)(tis)(tvds)1(peakdsV2ont1ont)(thgsVontt1LIccV)(tvdrive)(thgsV)(tids1LI1gsV0t4t1t2t3t1)(LdsIti11)()1(1232gsccLondspeakdsgdggonVVIRVCRttt[t2-t3]区间:图中蓝色Phase3这段轨迹。至t2时刻,MOSFET的DS电流已上升到外部电流并保持不变,导致GS电压保持不变。由于GS电压不变,驱动电流变成恒定并对GD电容进行充电,导致DS电容上的电压线性减小,直到到达饱和区的边界;推导见下页11[t2-t3]区间:MOSFET在t2时刻其DS电流已为IL1,此后GS电压保持不变,门极电流对Cgd充电,直到其进入饱和区的边界。11gggsccgdgdRVVdtdVC)1(12)(peakdsgsgdVVtV)1(1211)()(peakdsgsgdgggsccgdVVttCRVVtV1)1(111)()1(1232gsccpeakdsgdgggsccLondspeakdsgdggonVVVCRVVIRVCRttt113)(dsgsgdVVtV1)(1LondsdsIRV1)(13)(LondsgsgdIRVtV1)(1)1(12311)(LondsgspeakdsgsgdgggsccIRVVVttCRVVccV)(tvgs)(tis)(tvds)1(peakdsV2ont1ont)(thgsVontt1LIccV)(tvdrive)(thgsV)(tids1LI1gsV0t4t1t2t3tDGSgsCgdC)(tid)(tiLoV)(tvd)(tis)(tvds1ggR2ggRgV)(tids1LI1gsVccV11gggsccRVV方程初始值解t3时刻1)(1LondsdsIRV()()())1(1)(peakdsLondsVIR该间隔中DS电流保持不变,MOSFET的DS电压则可近似看成线性下降,间隔结束时下降到有对应的饱和电压。另外这个间隔中的二极管因电压反偏而截止。1gsV12开通过程的轨迹图开通过程的波形图dsVfsLthgsgsGIVV1)(1dsI1LI)(thgsV1ont2ont)1(peakdsVccgsVVPhase1Phase2Phase4Phase3ccV)(tvgs)(tis)(tvds)1(peakdsV2ont1ont)(thgsVontt1LIccV)(tvdrive)(thgsV)(tids1LI1gsV0t4t1t2t3t--[t3-t4]区间:图中绿色Phase4这段轨迹。MOSFET在t3时刻已进入饱和区边界,GS电压不再维持不变,Vcc继续对Cgs充电,GS电压继续上升,使MOSFET的通态电阻减小,从而DS电压也继续减小,直到t4时刻,GS电压上升到Vcc为止。由于这个间隔内,MOSFET的通态压降虽有减小,但变化不大,所以可不计为开通损耗,而将其看作通态损耗。)(tvgsDGSgsCgdC)(tid)(tiLoV)(tvd)(tis)(tvds1ggR2ggRgV)(tids1LIccV该间隔中的DS电压随着的继续增加,还会略略减小,间隔中虽然有损耗,但非常小。该间隔的时间也可以计算,但由于其损耗已不按开通损耗来算,所以就不需要这个数据了。gsV13ccV)(tvgs)(tis)(tvds)1(peakdsV2ont1ont)(thgsVontt1LIccV)(tvdrive)(thgsV)(tids1LI1gsV0t4t1t2t3t开通损耗:dttvtiTPdsttdssonturnonon)()(1210)(如电流、电压波形均用用线性近似,则有:sonLpeakdstttLononpeakdspeakdsspeakdstonLsdsttdssonturnftIVdtItttVVTdtVttITdttvtiTPonononononon1)1(112)1()1()1(0110)(21})]({[1][1)()(1211121其中:21onononttt1)(11lngsccthgsccgsggonVVVVCRt1)1(12gsccpeakdsgdggonVVVCRtfsLthgsgsGIVV1)(1142:MOSFET的关断过程原理--在t5前,MOSFET工作于导通状态,t5时,MOSFET被驱动关断;关断过程的轨迹图关断过程的波形图[t5-t6]区间:图中绿色Phase1这段轨迹。MOSFET的Cgs电压经驱动电路电阻放电而下降,使饱和区电阻微微上升,DS电压梢稍增加,但DS电流不变,直到t6时刻到达饱和区边界;)(tvgsDGSgsCgdC)(tid)(tiLoV)(tvd)(tis)(tvds2ggRgV)(tids1ggR2LI[t5-t6]区间的等效电路ccV)(tvgs)(tis2LI)(tvds)(thgsV1offt2offtt)2(peakdsV2gsVccV)(tvdriveofft)(tids2LI5t8t9t6t7tdsVdsI2LI)(thgsV2offtfsLthgsgsGIVV2)(21offt)2(peakdsVccgsVVPhase4Phase3Phase2Phase1因这个间隔内MOSFETDS电压很小,其损耗仍然可以计算到MOSFET的通态损耗之内,故这个间隔的时间不用计算。15--[t6-t7]区间:图中蓝色Phase2这段轨迹。在t6时刻,MOSFET进入放大区,因DS电流不变,导致GS电容电压不变,反向驱动电流变成恒定,并对GD电容放电,使DS电压继续增加。关断过程的轨迹图dsVdsI2LI)(thgsV2offtfsLthgsgsGIVV2)(21offt)2(peakdsVccgsVVPhase4Phase3Phase2Phase1ccV)(tvgs)(tis2LI)(tvds)(thgsV1offt2offtt)2(peakdsV2gsVccV)(tvdrive
本文标题:05-MOSFET在感性负载下的开关损耗公式推导
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