Design Of Two-stage Power Adapter Based On Half-bridge LLC Resonant Converter

Nowadays,consumer electronics products are popularized rapidly.The number of such products is enormous,and they will cause a lot of losses while charging.Therefore,developing a more efficient power adapter can save a lot of energy.In addition,according to the IEC61000 series of standards,power adapters with input power than 75 W must introduce power factor correction technology.Based on a large number of investigations and comparative studies,this paper gives a high-efficiency and highpower factor two-stage power adapter design scheme,and gives a detailed description of its working principle,control method and circuit design.First,this paper selects Boost PFC circuit and half-bridge LLC resonant converter as the front stage and back stage converters of the two-stage power adapter by comparing the advantages and disadvantages of different PFC topologies and resonant topologies.Secondly,this paper selects the average current control in the CCM mode as the control method of the front stage PFC circuit by comparing the advantages and disadvantages of the Boost converter when it operates in discontinuous,critical conduction and continuous mode,and then analyses the working principle of power factor correction for Boost converter.Thirdly,the topology of the back stage half-bridge LLC resonant converter is introduced,and its working principle and working process in different switching frequency ranges are analyzed.The First Harmonic Approximation(FHA)method was used to derive the equivalent circuit model of the back stage converter,and the DC gain characteristics,overload short-circuit and no-load characteristics of the converter were analyzed by Mathcad software.Finally,on the basis of theoretical analysis,this paper designs the main circuit and control circuit of the front and back stages of the power adapter and produces a prototype power adapter with an output power of 70 W.In addition,this paper also testes the power factor,soft switching,starting voltage,power-down time,output ripple etc.At the same time,the collected waveforms are analyzed and summarized to verify the feasibility of the design scheme.