Light load efficiency improvement for multi-channel PFC

With the fast growing information technologies, AC-DC front-end power supply design is facing extremely tough challenges due to the continuously increasing power density and efficiency requirement. For the PFC stage, how to reduce the boost inductor and the EMI filter size without compromising the efficiency is the key to meet the challenges. Lots of techniques has been studied and proposed during the last several years. Among these techniques, multi-channel interleaving is a quite promising one. By staggering the channels at uniform intervals, multi-channel interleaved PFC can reduce the EMI filter size significantly due to the ripple cancellation effect. In addition, the interleaving multi-channel configuration makes it possible to implement the phase-shedding to improve the PFC light load efficiency. Today, the power supply industry is spending tremendous effort on improving the PFC light efficiency due to the economic reasons and environmental concerns. By decreasing the number of active channels according to the load, the PFC light load efficiency can be optimized. In this paper, the phaseshedding control is proposed to improve the PFC light load efficiency and the issues on the EMI filter design are investigated. To improve the light load efficiency without compromising the EMI filter size, the asymmetrical phase angle control strategy is proposed, and is verified and demonstrated by the experimental results.