| Switching power supply is widely used in power system, communication system, computer system, lighting, air conditioning and other household appliances and other fields. The development trend of DC/DC converter is the switching power supplies which are high frequency, high power density and high efficiency, and at the same time suppress the harmonic pollution. Traditional hard-switched converter limits the improvement of switching frequency, power density and efficiency. Therefore, it is significant to research the new type which has the function of inhibiting harmonic pollution and the highly efficient of soft switching converter for improving power quality, energy conservation.According to the development trend of switching power supply, the design of APFC+LLC resonant converter is two stage of switch power supply in this paper. Switching power supply front stage adopts the boost of APFC technology, which achieves a stable output voltage 400V. According to the working principle of APFC, pre-stage circuit established the main circuit element parameters and models of the former circuit. By using the UC3854 chip and the design of its peripheral circuit, pre-stage circuit realizes double closed loop control of the main circuit.The switching power backward stage supplies half bridge LLC resonant circuit to realize the DC/DC conversion. LLC resonant converter is easy to achieve soft drive technology and easy integration of resonant inductor. According to the requirement of design, after calculating the parameters of LLC resonant converter, a 24V120W experimental prototype is developed with L6599 chip to control the main circuit and transformer winding through the magnetic integration technology.Finally, the design of prototype is debugged. The results of experimental waveforms and data show that the switching power can be achieved APFC, and backward stage has the functions of soft switching technology, which is proven the rationality and validity of the previous theoretical analysis. |
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