The Microwave Frequency The Llc Resonant Soft-switching Power

As microwave oven widespreadly used in common families, its efficiency, volume and intellectualization are cared more and more. Traditional power supply for magnetron in microwave oven was composed with an industrial frequency transformer and a half-wave rectifying circuit, it has many drawbacks. On the basis of fully understanding the working characteristics of magnetron, a novel power supply for magnetron in microwave oven was developed based on LLC resonant converter and voltage doubler rectifier circuit. The novel supply has smaller volume and weight, higher efficiency, and more intelligent. The contents of the paper is listed as follows:(1) LLC resonant converter was studied on deeply, working process of the circuit was analysed when fm<fs<fr,fs=fr and fs>fr. Voltage gain and resonant current were derived based on the first harmonic approximation (FHA) approach, and the necessary condition for the ZVS of the half bridge switch tubes was derived. Design method of main parameters of LLC resonant converter was optimized.(2) Combined with input and output parameters in real, detailed calculation was carried out for parameters of main circuit of the LLC resonant soft-switching power supply used in microwave oven, including selection of components in rectifier filter circuit, selection of switch tubes, design of resonant inductor and capacitance. Three magnetic components were integrated in a transformer, so number of components and core loss could be reduced.(3) Control system of the soft-switching power supply for magnetron was designed based on a single chip microcomputer PIC16F684, including auxiliary power supply, detection circuit and driver circuit. Program of microcomputer was compiled in C programming language.Experiments were carried out and experimental waveforms were obtained. The experiments and applications show that the soft-switching control of the power supply can be implemented safely and reliably in the range of switching frequency variation, the output voltage of the power supply can satisfy demands of magnetrons, and the output power of magnetrons can be regulated continuously.