Hybrid phase shifted full bridge and LLC half bridge DC-DC converter for low-voltage and high-current output applications

Abstract

A hybrid phase shifted full bridge (PSFB) and LLC half bridge (HB) DC-DC converter for low-voltage and high-current output applications is proposed in this study. The PSFB shares its lagging leg with the LLC-HB and their outputs are parallel connected. When the output current is small, the energy of LLC circuit in combination with the energy stored in the leakage inductance of PSFB's transformer can help the lagging leg switches to achieve zero voltage switching (ZVS) turn on, which can reduce voltage stress and avoid annoying voltage spikes over switches. For the power distribution at rated power, the PSFB converter undergoes most of the power whereas the LLC-HB converter working as an auxiliary part converts only a small portion of the total power. To improve the conversion efficiency, synchronous rectification technique for the PSFB DC-DC converter is implemented. The design principle is given in view of ZVS for lagging leg switches and low transconductance of LLC converter. The validity of the proposed converter has been verified by experimental results of a 2.5 kW prototype.