Systematic design of dissipative and regenerative snubbers

Current commutation between diodes and switches is possible in hard-switching power stages over a wide di/dt range (10-1000+A/ mu s) with modern power devices and hardware practice. However, a definitive procedure does not exist for setting di/dt at diode reverse recovery. Diode turn-off performance is therefore examined, using IGBTs (insulated-gate bipolar transistors) to switch the diode current, to establish whether there exists an optimal di/dt that minimizes energy loss associated with diode recovery, when simple snubber-inductance reset circuits are used. Destructive parasitic oscillation, induced in inverse-parallel IGBTs across reverse-recovering freewheel diodes in IGBT modules, was observed during experimentation. The results indicate that snubberless power-stage operation, where active snubbing must be used to control switching transitions, is fundamentally less efficient than the best passive snubbing methods, that operation of diodes at very high di/dt is undesirable, and that very stiff power-switch drive circuits can lead to device failure in snubberless power stages.<<ETX>>