Research On Half-bridge LLC-4 Resonant Converter

In recent years, LLC resonant converter has been researched popularly in power electronics field. The chief advantages of LLC resonant converter consist of simple structure, wide input voltage, high efficiency,high power density and high magnetic integration level .Owing to the resonant characteristics in itself, the converter can synchronously realize soft switching of power switches on primary and secondary side without additional buffer circuit. According to the points above, LLC resonant converter fits into the develop trend of switching power supply.Firstly, the paper introduces the development of resonant converter and variable structures to LLC converter and lays stress on the forth LLC resonant converter(LLC-4)after a comparison. Then, the paper analysis the modes of the converter working in different frequency band and deduces the mathematic expression to the wave of main resonant elements. On that basis , a completely improved parameter design strategy comes out in terms of frequency domain and time domain analysis. And then, three methods about current limited to the LLC resonant converter under over load have been introduced and the method which involves assistant transformer is illuminated in detail as well as the parameter design to the method. Meanwhile, the paper introduces the way to decrease the standby loss and analysis the modes of the LLC resonant converter working under light or no load. Afterwards, the transformer is designed respectively employed traditional shape and planar shape .At the end of the paper, a 210W LLC half-bridge resonant converter prototype is built up , which involves detailed parameter design and control circuit design .Variable wave graphs under different load display to verify the feasibility of the theoretical strategy. Finally, the loss analysis to rated load is given and the outcome leads to the subsequent improved research.