Design and measurement considerations for WBG switching circuits

Wide Band Gap (WBG) transistors using materials such as Gallium Nitride (GaN) and Silicon Carbide (SiC) offer superior electrical and thermal properties, as well as fast switching capability. However, the high dv/dt and high di/dt may cause ringing with the parasitic inductances and capacitances in the switching loop, increasing overshoot voltages and reducing confidence in the design. Also, making accurate measurements of the switching behaviour without unduly loading the circuit under test is challenging and further impedes the development of WBG applications. This paper presents a prototype WBG Development Platform, built around a half-bridge switched inductive load test circuit. Additional circuits are integrated on to the main PCB for test and measurement purposes: These include a high bandwidth linear current gate-drive circuit and a high bandwidth on-board measurement system. These sub-circuits are described in detail in this paper, together with the switching waveforms that have been achieved during tests with SiC MOSFETs. The authors demonstrate a practical implementation for high frequency WBG power circuits.