Analysis of the zero-current-switched quasiresonant converters used as power factor preregulators

The use of zero-current-switched quasi-resonant converters (ZCS-QRCs) as power factor preregulators (PFPs) is studied. The study is applicable to boost, buck-boost, flyback, SEPIC, and Cuk topologies. The main conclusion is that the switching frequency variation range using a half-wave resonant switch is lower than that using a full-wave resonant switch if the load connected to the output is almost constant. Moreover, using topologies with a transformer (flyback, SEPIC or Cuk), this variation range can be minimized choosing an adequate value of the normalized switching frequency at the peak of the sinusoidal input voltage. However. this range increases greatly when the load changes in the same manner. In this case, a reduced switching frequency variation range is obtained using a full-wave switch. However, this type of resonant switch decreases the efficiency because it handles reactive energy, and then a trade-off between switching frequency variation range and efficiency must be considered