A 500 kHz, 3.3 kW boost PFC with low loss coupled auxiliary ZVT circuit

The paper presents a low-loss auxiliary circuit in a power factor correction (PFC) circuit to achieve zero voltage transition and hence improving the efficiency and operating frequency. The high dynamic energy generated in the switching node during turn-on is diverted by providing a parallel path through a coupled auxiliary inductor and a transistor placed across the main inductor. The auxiliary devices operate with soft-switching at both turn-on and turn-off instances and this addition has no effect on the control of the main PFC circuit. Using a coupled inductor reduces the losses in the auxiliary circuit in addition to the inherent loss savings in the main PFC switch. The paper discusses the theoretical analysis, operating principles and design of the proposed scheme in detail and validated with an hardware showing experimental results on a 3.3 kW/ 500 kHz PFC prototype.