Interleaving Multi-Channel PFC with Improved Light Load Efficiency (2007)
High light load efficiency is becoming more and more demanded in recently years. With the multi-channel structure, it has been demonstrated that shut down some channels can effectively improve the efficiency at light load conditions. However, for the PFC case, due to the EMI requirement, the EMI filter needs to handle the worst case EMI noise. Thus, the benefit on filter size reduction from multi-channel interleaving is lost. Based on the asymmetrical interleaving method, adaptively controlled interleaving multi-channel PFC is proposed to improve the light load efficiency without compromising the EMI filter size. The concept can be demonstrated with a 3-channel interleaved PFC with 130 kHz switching frequency. At full load condition, all 3 channels are operating with 60°phase shift. At light load condition, 1 channel is shut down, 2 channels are operating with 90°phase shift to keep high efficiency and high filter corner frequency. The EMI filter can be designed based on 2-channel 90° phase shift operation. The corner frequency difference between 2-channel and 3-channel is significantly reduced. By applying this proposed controlled method, the light load efficiency of multi-channel interleaving PFC can be improved without compromising the benefit on the EMI filter size.