| Abstrakt: |
The recent development and commercialization of wide bandgap (WBG) power semiconductors, specifically gallium nitride (GaN) and silicon carbide (SiC), have driven the increase in switching frequency for soft-switching power converters, such as the Class E, Class ${\Phi _{2}}$ , and Class DE resonant inverters and rectifiers. However, prior literature has characterized numerous commercial GaN and SiC devices using the Sawyer–Tower circuit and discovered significant large-signal ${C_{\mathrm{ oss}}}$ charge-voltage hysteresis. This ${C_{\mathrm{ oss}}}$ hysteresis, equivalent to OFF-state energy loss, is highly dependent on the frequency and voltage across the device, hindering the efficiency and performance of MHz-range soft-switched converters. This article is the first to explain the origin of the ${C_{\mathrm{ oss}}}$ loss in SiC power devices as charging and discharging conduction losses at the termination of the device. The loss characteristics relative to the operating voltage, frequency, ${dV/dt}$ , and temperature are dictated by incomplete ionization. Incomplete ionization also highlights a significant inconsistency between the large-signal ${C_{\mathrm{ oss}}}$ behavior and small-signal behaviors, which is often the model used in manufacturers’ datasheets and SPICE simulations. The large-signal charge–voltage behavior is transient, where the charge in ${C_{\mathrm{ oss}}}$ depends on the rate of the voltage swing across the device. We validate these hypotheses through mixed-mode simulations using the Sentaurus technology computer-aided design (TCAD) and experimentally using commercial and custom SiC devices. |
