Design Of Single-ended Resonant Converter Applied In Magnetron Of Microwave Oven

Household microwave ovens have been recognized by more people. Therefore, the intelligence, volume, efficiency and other aspects of microwave ovens received more attention. Early power supplies for magnetron in microwave ovens were composed with an industrial frequency transformer and the half-wave rectifying circuit. The drawback is unadjustable, high energy consumption and heavy weight.To follow modern trend, this subject attempts to develop a continuous adjustable power supply for the magnetron to replace the traditional intermittent one, which has higher efficiency and longer life, combining double voltage rectifying and resonance shift, using soft starter to eliminate the inrush current produced by the linear transformer, and carrying the resonance technology of ZVS to reduce switch loss.The main contents of the subject are outlined as follows:1. After simple comparison of common resonant circuits, single-end of LLC resonant topology is selected. The topology is studied in-depth, with the situation analysis of different working stages. DC gain, the normalized impedance characteristic parameters and the neeessary condition for the ZVS of the LLC resonant circuit are derived by the first harmonic approximation(FHA) approach.2. According to the target parameters, parameters of main devices composing the single-ended resonant converter are calculated in detail, the selections of input and output rectifier filtering device, switch type and model, resonant inductor and capacitor, are completed, and the practical transformer is designed using the magnetic-integration techniques.The design is analysed by SABER simulation, and is proved to be feasible.3. The power supply system is designed based on the chip S3F84B8 produced by Samsung, including main circuits and interactive parts with upper control chip. Main circuits include: auxiliary power circuits, the input current and voltage detection circuits, surge protection circuits, switch drive circuits and phase detection circuits.4. A prototype of switch power supply, whose output power rated at 1.3KW, is built and tested. Compared with the theoretical analysis, the datas show that the converter can achieve ZVS opened, with excellent working efficiency and high power factor.