Research On Current Adaptive Resonant Loop Soft Switching Full Bridge Converter

High frequency is one of the important development directions in Switching Power Supply technology, and it is the foundation of miniaturization and modularization. The switching loss of the traditional hard switching converter is proportional to the switching frequency, the higher the switching frequency, the greater the switching loss, the lower the conversion efficiency. In order to make the Switching Power Supply operating at high frequency and efficiency, soft switching technology has received extensive attention. But the amplitude of resonant current for any one of the most present soft switching techniques is fixed and invariable at home and abroad, without mentioning is variable and self-adaptable to the load current. This paper presents a Current Adaptive Resonant Loop (CARL) soft switching full bridge converter, which not only realizes Zero Current Switching (ZCS), but also the amplitude of resonant current follows load current automatically to reduce switching loss and improve the efficiency of power converters.Firstly, according to the disadvantage of hard switching converter in high frequency operation, soft switching technology is introduced. Considering amplitude of resonant current can’t change and switch mode between hard and soft switch can’t interchange in soft switching topology of ZCS PWM Buck converter, CARL soft switching resonant unit is proposed. Adding the CARL soft switching resonant unit to the full bridge converter, a new soft switching topology is obtained. According to the existing problems of this topology, it obtains CARL soft switching full bridge converter. Then, the working principle and ZCS condition is studied. Finally, it discusses light load characteristics, voltage oscillation of auxiliary switch and rectifier diode, loss and design principle of resonant parameters. It not only realizes the ZCS, but also changes the amplitude of the resonant current along with the load, which reduces the additional conduction loss and improves efficiency over a wide load range.The paper provides the design of a 3kW prototype, and analyzes the design process of main circuit, control circuit and high frequency transformer and so on. Then the PSIM simulation model is built to analyze the switching characteristics, relationship between amplitude of the resonant current and load current and RC sunbber of auxiliary switch tube and rectifier diode, which proves the correctness of the theoretical analysis. Finally, it offers current and voltage waveforms of main switch, waveforms of resonant current and resonant capacitor voltage and efficiency. The experimental results show that it achieves ZCS over a wide load range and amplitude of resonant current decreases with load current, which improves efficiency, especially at light load.