Characterization and Optimal Control of Totem-Pole PFC Converter With High Frequency GaN HEMTs and Low Frequency Si Diodes

A cost-effective totem-pole power factor correction converter with high-frequency gallium nitride high electron-mobility transistors and low-frequency Si diodes is investigated in this article. The reverse recovery characteristics of low-frequency diodes are evaluated experimentally. With the slow recovery characteristics, a negative current can flow through the low frequency diode, so that soft-switching and critical mode operation is achieved easily. However, if the duration of the negative current exceeds the reverse recovery time of the low-frequency diode, the diode will switch at high frequency, leading to severe losses and losing control of the inductor current. In order to avoid this issue, an adaptive off-time soft-switching strategy is adopted, and discontinuous conduction mode operation is suggested near the zero crossing of the grid voltage. Furthermore, since only the low-frequency grid current is sampled, this control strategy has the merits of low requirements on control resources and low cost. Experimental results of a 400W prototype are provided to verify the effectiveness of the proposed control strategy.