L6599 Is Based On The Development Of Multi-resonant Half-bridge LLC Converter

Airborne radar receiver to the index requirement of the power supply is very high, especially the ripple asked less than a few millivolts. And ordinary switching power supply output ripple are generally higher, up to tens of millivolts or more, and the switch peak interference caused by the ripple is very difficult to suppress. Therefore, the application of a switching power supply to replace the linear power supply to the receiver, must solve the problem is to reduce the output of the switch power supply ripple and interference! To effectively reduce the output ripple, you must suppress interference sources, interference sources are mainly concentrated in the switch circuit and the output rectifier circuit, so the soft switch technology research and application become inevitable. Resonant converter with soft switching characteristics and good EMI performance, is the transmission and improve the effective of the sensitivity of restraining measures!Although resonant power converters have advantages of high efficiency and low noise, the series resonant converter (SRC) suffers from several limitations. First, the converter is theoretically incapable of regulating under unloaded condition. Second, wide frequency variation is necessary to provide regulation over full load range. Third, at a light load, small resonant current makes that zero voltage switching (ZVS) is lost. Finally, output voltage regulation at a light load is difficult in the controller design. In addition, for a parallel resonant converter (PRC), circulating energy will hurt the high line or light load efficiency. The LLC resonant converter overcomes several drawbacks of conventional resonant converters with its simple structure. The advantages of the LLC resonant topology are:Output regulation over wide line and load variations with small variations of switching frequency、ZVS capability for entire load range、low turn-off current, therefore the switching loss is very low. Multi-resonant network makes that the magnetic components can be easily integrated into one magnetic core. As a result, the leakage inductance of a transformer can participate in resonant network. There are low voltage stress and zero current switching (ZCS) on secondary rectifier. No secondary filter inductor makes low voltage stress on rectifier diodes limited to two times output voltage. In addition, ZCS of secondary diodes removes its reverse recovery problem.In this paper, the theoretical analysis and optimal design of the LLC resonant converter is proposed. The characteristics and advantages of this converter are explained. In addition, the equivalent circuit and operational principle are derived to analyze the LLC resonant converter. The ZVS and ZCS conditions of MOSFETs and output rectifiers are derived by the equations of the primary current waveform. The efficiency and cost optimal designations are suggested by focusing on the resonant components and switching frequencies. From the experimental results obtained from the200W SMPS sample, the LLC resonant converter shows very high efficiency under the high input voltage and full load condition.