Considerations when designing with wide bandgap devices

Designing with wide bandgap devices, such as silicon carbide (SiC) and gallium nitride (GaN), presents unique challenges for power conversion electronics. While these devices are known for their low-loss properties, they also require careful consideration in areas such as gate drive, avalanche and short-circuit performance, and reverse conduction effects.

Gate drive is a critical aspect in the use of SiC and GaN devices, as it is more difficult than with traditional technologies such as IGBTs and MOSFETs. These devices typically have lower gate thresholds and hysteresis, which can reduce substantially at high temperatures. To avoid phantom turn-on, gates often have to be driven with a negative off-state voltage. Additionally, the fast dV/dt of these devices can couple transients into the gate through the drain-gate Miller capacitance, which can be problematic. To mitigate these effects, manufacturers often offer Kelvin connections to the source and added series gate resistance and/or snubbers.

Avalanche and short-circuit performance is also a consideration when using wide bandgap devices. IGBTs and silicon MOSFETs have an avalanche rating for their ability to withstand energy from an overvoltage at the collector/drain. However, this information is not yet easily available for SiC-MOSFETs, and GaN cells do not have the ability to survive overvoltage and will immediately fail. SiC-MOSFETs do have a short-circuit rating, but this is less well-defined for GaN devices. Despite these challenges.