Noncirculating current series resonant converter with pulse frequency modulation

SummaryIn this paper, an asymmetric pulse frequency modulation (APFM) is applied to the full‐bridge series resonant converter with a secondary LC resonant tank. Different from the traditional PFM, the upper and lower switches have complementary gate drivers and the lower switches have constant on time of half‐resonant period in this paper. Thanks to the resonant tank moved to the secondary side with the adopted APFM, the maximum magnetic flux density Bm of a high‐frequency transformer (HFT) is only concerned with the fixed resonant frequency rather than the variable switching frequency. Hence, the switching frequency can be widely regulated, as well as the voltage gain. Furthermore, the circulating current flowing back to the input voltage source in the traditional LC series resonant converter can be eliminated by the APFM, leading to a low resonant current peak value. The operation principles and characteristics of the adopted method are analyzed in detail. Finally, a 500 W/70–120 V to 300 V/21–180 kHz prototype is built, and the experimental results verified the theoretical analysis well.