Research On Current-Driven Synchronous Rectifier For LLC Resonant Converter

High efficiency and high power density have become one of the most significant trends in power electronic products.With merit in conversion efficiency and power density,LLC resonant DC/DC converter is very popular nowadays.However,the secondary-side loss always contributes a large part of the total power loss,especially in high output current application.Therefore based on the analysis of operation principle of the LLC resonant converter and the characteristics of different rectifiers, this paper makes a comparison among different synchronous rectifier(SR) technologies,especially concentrating on the research of current-driven SR.Due to detailed study about the LLC resonant converter with center-tapped rectifier,this paper analyzes and designs a secondary-side current-driven synchronous rectifier.As the current transformer(CT) takes a lot of space in the secondary side, which also makes the design of PCB layout more difficult.So the primary-side current-driven synchronous rectifier is reviewed and analyzed.With a simple transformer structure and low voltage stress across secondary-side rectifier,Voltage-doubler rectifier is used in many application areas.This paper proposed a new current-driven synchronous rectifier employing one CT with two secondary-side windings,which reduces the number of CT as well as the loss brought by the driving scheme.Other current driven SR schemes are also discussed in this paper,such as current driving SR(CDSR) with energy feedback for the high side and CDSR using CT with only one secondary-side winding.The full-bridge rectifier also has been analyzed in this paper.The full-bridge rectifier also has a simple-structure transformer and low voltage stress across the secondary-side rectifiers.However,the driving conventional scheme for 4 SRs is too complex.This paper proposed a novel hybrid driving method as voltage driving scheme for high-side SRs and current driving scheme for low-side SRs.It just needs one single-secondary-winding CT and one transformer auxiliary winding,which makes the whole driving scheme very simple.