Soft switching for power factor correction for server power supply unit

Soft switching for power factor collection (PFC) of high-end server power supply unit (PSU) is studied. FET loss of PFC circuit is caused by Ron-related loss and switching loss. The switching loss consists of switching-speed-related part and output capacitance (Coss)-related part. The switching-speed related-part can be reduced by using a high-speed FET and high-power gate driver; however, Coss-related loss remains constant and makes efficiency worse especially in low-load region. We propose a new soft switching PFC circuit designed for Coss-related loss reduction and demonstrated that the PFC loss was reduced by half at 20% load with both SPICE simulation and prototype circuit. In the data server case, the average load of the PSU is usually less than 30% [1] when redundant PSU is used, so this circuit is very effective for energy saving of data center.