Investigation of an overvoltage protection for fast switching silicon carbide transistors

Transistors made of wide band-gap materials such as silicon carbide (SiC) offer the opportunity of much faster switching, and, hence, lower switching losses compared with silicon (Si) devices. To utilise the full potential of SiC-devices the influence of stray inductances and capacitances on the switching behaviour has to be minimised. Stray inductances result in overvoltages possibly destroying the transistor at turn-off. These overvoltages can be avoided by protective circuitries such as active clamping or dynamic voltage rise control without sacrificing the fast switching. Such circuitries are well-known from Si-transistor drivers and are used in cases where stray inductances cannot be reduced any further. All investigations of the overvoltage reduction by the dynamic voltage rise control (DVRC) were performed for one SiC-BJT and two SiC-MOSFETs from different manufacturers. If the DVRC would behave in a similar way such as for silicon IGBTs, the benefit would be huge: Overvoltages would be reduced and the switching speed could be increased. However the influence of parasitic components has to be considered for the protective circuitry as well.