New Insights on Output Capacitance Losses in Wide-Band-Gap Transistors

The low ON-resistance of wide-band-gap (WBG) transistors is a key feature for efficient power converters; however, the anomalous loss in their output capacitance (C-OSS) severely limits their performance at high switching frequencies. Characterizing C-OSS losses based on the large-signal measurement methods requires an extensive effort, as separate measurements are needed at different operation points, including voltage swing, frequency, and dv/dt. Furthermore, there is a practical tradeoff in the maximum voltage and frequency applied to the device. Here, we introduce a new circuit model, including an effective C-OSS and a frequency-dependent series resistance, along with a simple small-signal method to fully characterize C-OSS losses in WBG transistors. The method accurately predicts C-OSS losses at any voltage swing or frequency. Contrary to other methods, this technique directly leads to a general identification of C-OSS losses at different operation points, revealing new insights on C-OSS losses in WBG transistors, especially the dependence of E-DISS on voltage and frequency. Based on the proposed approach, the issue of C-OSS losses in enhancement-mode GaN and SiC transistors was assigned to the limited quality factor of C-OSS. The precise characterization of C-OSS losses proposed in this letter is essential for designing efficient high-frequency power converters.