(2) Polarized R-C snubbers (有极性RC缓冲电路)·Used as turn-off snubbersto shape the turn-offswitchingtrajectoryof controlled switches.: Used as overvoltage snubbers to clamp voltagesapplied to controlled switches to safe values.. Limit dvldt during device turn-off
(2) Polarized R-C snubbers (有极性RC缓冲电路) •Used as turn-off snubbers to shape the turn-off switching trajectory of controlled switches. • Used as overvoltage snubbers to clamp voltages applied to controlled switches to safe values. • Limit dv/dt during device turn-off
(3) Polarized L-R snubbers (有极性LR缓冲电路)·Used as turn-on snubbers to shape the turn-onswitchingtrajectory of controlled switches. Limit di/dt during device turn-on-DSnubberDLcircuitVdVdD-↑
(3) Polarized L-R snubbers (有极性LR缓冲电路) •Used as turn-on snubbers to shape the turn-on switching trajectory of controlled switches. • Limit di/dt during device turn-on Vd + - Ls DLs Df RLs Io Sw DLs RLs Io - Sw Df + Snubber Ls circuit Vd
27-2 Diode Snubber Circuit1SwitchingWaveformsA power diode requires a finite time to switch from blockingstate to the on state (forward bias) and vice versa.Qr=1rrtr/2Forward-recoverydir/dt0.25lrdip/dtvoltaae(正向恢复幢电压VFPThe overshoot of thevoltage during turn-onisnotobservedVonVFPForward-recoverytime(正向恢复时t5间) (tr=t}+t2)t4
27-2 Diode Snubber Circuit IF t diF/dt Vrr t3 t2 1 t5 VFP t Von 0.25Irr trr Qrr=Irrtrr/2 t5 t4 S= Irr VR t4 diR/dt 1 Switching Waveforms A power diode requires a finite time to switch from blocking state to the on state (forward bias) and vice versa. Forward-recovery voltage(正向恢复 峰值电压) VFP The overshoot of the voltage during turnon is not observed. t Forward-recovery time(正向恢复时 间) (tfr=t1+t2 )
27-2 Diode Snubber CircuitReverse-recoveryQrr=lrtrr/2voltage(反向恢复dir/dt0.25lrdi,/dt幢电压VrrReverse-recoverycurrent反向恢复Von幢电流1VFPReverse-recoveryHrit5time(反向恢复时4Tr
27-2 Diode Snubber Circuit Reverse-recovery time(反向恢复时 间) trr Reverse-recovery voltage(反向恢复 峰值电压) V rr IF t diF /dt Vrr t3 t2 t1 t5 VFP t Von 0.25Irr trr Qrr=Irrtrr/2 t5 t4 S= Irr VR t4 diR/dt Reverse-recovery current(反向恢复 峰值电流) Irr
27-2 Diode Snubber CircuitQrr=lrrtrr/2Reverse-recoverydir/dt0.25lrrdip/dtcharge（反向恢复葡 Qr=1rtr/2"snappiness"factor（恢复系数）VonVFPS=ts/t4VFt.rt5S=t4Soft-recovery diode（软恢复二极管: ts>>t4Abrupt-recovery diode（硬恢复二极管):ts<<t4
27-2 Diode Snubber Circuit Reverse-recovery charge (反向恢复 电荷) Qrr=Irrtrr/2 “snappiness” factor (恢复系数) S=t5 /t4 IF t diF/dt Vrr t3 t2 t1 t5 VFP t Von 0.25Irr trr Qrr=Irrtrr/2 t 5 t 4 S= Irr VR t4 diR/dt Soft-recovery diode (软恢复二极管): t5>>t4 Abrupt-recovery diode (硬恢复二极管): t5<<t4