Research On Full Bridge LLC Resonant Converter

With the development of the switching power supply toward the high frenquency,efficiency and power density, the traditional hard switching appears a lot of problems in theapplication. To solve these problems, the soft switching technology comes into being. As akind of soft switching, the resonance switching converter has the advantages of highfrequency, low loss, high efficiency, small size, and so on. As the LLC resonant powerconverter can achieve both ZVS of the primary switch and ZCS of the rectifier diode in fullload range and have the advantages of easy integrating, wide input voltage range and so on, itgets wide attention and application in the high frequency switching field.Firstly, the basic classification of resonant converters and the advantages anddisadvantages of various resonant converters are analyzed in this paper. On this basis, notonly the working principle but also the frequency characteristic, no-load characteristic andshort-citcuit characteristic of the converter are discussed in detail. And the impacts of theparameters on the converter are pointed out. In addition, the high performance resonant modecontroller MC33067is selected as the main control chip of the converter. The detailed designprocess of the converter’s main and drive circuits are investigated, including the parameters’calculation and selection of main switch, rectifier diode and output filter capacitor. Especially,the selecting basis and design method of the resonance elements (e.g. the resonant inductor,capacitor and so on) and magnetic elements (such as the main transformer and drivetransformer, etc.) are given. Finally, Saber software is adopted to simulate and analyze themain circuit of the converter. An experimental prototype is set up, and some problems, e.g.,the converter can’t work on the inductive state and the operating frequency can’t be linearchange, in the experiment are analyzed in detail and the corresponding solutions are given.A500W full-bridge LLC resonant converter prototype is designed in this paper.Waveforms of switch, resonant current and the output ripple voltage can be obtainedaccording to the prototype test. It proves that the theoretical research and design method in this paper are reasonable and feasible.