Research On Digital Synchronous Rectification Technology Of LLC Resonant Converter

With the development of switching power supply towards high frequency,high efficiency and high power density,resonant converter circuits are widely used because of its easy implementation of soft switching.Especially,the LLC resonant converter,which can achieve soft switching in full load range,has high efficiency and simple circuit structure.It has become one of the mainstream circuit topology.Firstly,this paper introduces the working modes of half bridge LLC resonant converter and analyzes its working process in detail.Then,this paper designs the resonant network parameters of the converter through the voltage gain curve obtained by the first harmonic approximation method,and performs the circuit simulation verification at the same time.According to the circuit parameters after simulation,the planar transformer of the converter is analyzed and designed,which effectively reduces the volume of the converter and improves the power density.In low voltage and high current applications,the loss of rectifier diodes in LLC resonant converter's rectifier circuit is usually large.In order to improve efficiency,it is necessary to use MOS tube with small conduction resistance instead of diode,which is called synchronous rectification technology.Synchronous rectification has many driving modes.The driving mode controlled by current is more precise and effective,but its driving circuit is complex,which is not conducive to improving the power density of the converter.In this paper,a new control algorithm is proposed based on a universal adaptive synchronous rectification technology.The algorithm uses digital signal processor to capture the conduction time of the body diode of synchronous rectifier tube,and controls the duty cycle of the drive signal to adjust the next cycle of synchronous rectifier tube,so that the synchronous rectification achieves an ideal effect and improves the efficiency of the converter.Finally,the experimental verification of the proposed synchronous rectification control algorithm is carried out in this paper.