| Half-brigde LLC resonant circuit can relize power converter’s ZVS for primary side switchs,easy to achieve ZCS for secondery rectifier diodes, reduce the switching loss,improve the efficiency,by controlling frequency and optimizing resonant parameters.This convertor can maintains the good performences, geatly reduce the volume, boost the power density while operating in MHZ frequency. The half-bridge LLC convertor will become one of the main stream circuit topology in the future.In this paper,the operating principle of half-bridge LLC cinvertor was analysted in detail.The steady-state model was builded using First Harmonic Apporximation,and the DC charaeteristies was deduced.The influnce of main parameters for DC charaeteristies and the input impedance characteristics of the resonant network were researched.Base on the deep sduties, constraints of the ZVS switching tube was proposed and the parameters of the main circuit were designed.The small signal circuit model was setted up by employing equivalent circuit method. the regulator of control circuit was designed base on the small signal circuit.The digital control method applying in the switching power supply can simplify the complexity of circuit design;The program possess good portability, easy to modify, and was not easily affected by environment around.Thus, digital control method will be a current potaintial method in the fied of switching power supply. In this paper, the frequency in the resonant circuit was modulated using the digital controller of TMS320F2812.The PI algorithm was presented.Moreover, driving circuit, voltage and current sampling filter circuit, and the protection circuit were discussed.A480W/48V experimental circuit was buided after the complitment in design of main circuit parameters and regulator. Some of the significant experimental waveform were given at last.The result demonstrate stable performance and realize ZVS in the primary side switchs.the correctness of the theory was verified. |
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