Design Considerations for Series-Connected SiC MOSFETs Operating at 100 kV/µs

Abstract

Series connection of Silicon Carbide (SiC) metal-oxide semiconductor field-effect transistors (MOSFETs) is an interesting solution to design switches for voltages that are not yet commercially available or limited for single-die devices. However, inherent static and dynamic voltage balancing issues in a serialized stack need to be addressed. Most of the balancing techniques shown in literature are based on active snubber and adaptive driver circuits requiring complex circuitry, with high component counts, complex control schemes and high-speed voltage and current sensors. Moreover, such circuits are difficult to tune for optimal operation, especially for adaptive operation under load variations. The RC snubber, on the other hand, is a simple circuit, with low component count. The aim of this paper is to investigate the design and tuning limits of RC snubber circuits and non-adaptive, standard, voltage-source gate drivers for achieving the best-balancing transient and steady-state voltage distributions among series-connected discrete SiC MOSFETs operating at speeds higher than 100 kV/µs. Furthermore, the effect of device parameters spread has been studied. It has been shown that a larger parameter mismatch will lead uneven switching energy losses. However, the anticipated voltage balance and increased switching losses are still within an acceptable range.