A Study On The Novel Single-Transistor Forward-Flyback Convertor

With the constant progress of the society and the continuous development of science and technology, switching power supply technology is more and more widely used in modern power electronic products. Because of the new energy power generation, military, mining, communications and other fields demand for the converter input voltage range is particular high, wide input range converter is widely used. In this thesis, sectional content of this thesis is as follow:analysis of the wide range of input voltage converter main performance requirements and basic features; summary about several class of converters possess excellent performance on wide input range occasion; research and summary about the characteristics of forward, flyback, forward-flyback converters. More ever, on the basis of forward and flyback converter, a novel forward-flyback converter adjust to wide input range is created, which through add a capacitor and replace a diode with a mosfet.In order to solve the problem of high voltage stress and voltage spike caused by leakage inductance that traditional single tube converters inherent possess, symmetric RCD clamp circuit is applied to novel forward-flyback converter. Mode analysis and theoretical research on MCCM (magnetizing current continuous mode) show that novel converter has the advantage of high efficiency, duty cycle D can be greater than 0.5 and low voltage stress which traditional forward converter in a symmetric RCD clamp possess, at the same time, the new forward-flyback converter further broaden the input voltage range and increase the output voltage gain.In purpose of improve the efficiency, a regenerative clamp circuit is imported to the novel forward-flyback converter. Reaserch on MDCM(magnetizing current discontinuous mode) of the novel converter and discussion of clamp capacitor is made. As a result, the novel converter in regenerative clamp circuit possess the advantage of RCD clamp mode and the leahage inductance energy is completely recycled, what futher promote the efficiency.On the occasion of low voltage and high current, the efficiency of converter is badly effected by the loss on rectifier diode. In this thesis, synchronous rectification technology is further discussed to apply to novel converter and computer simulation design is implemented, what provide a feasible program for the new forward-flyback converter under low voltage and high current.Finally, prototype based on the novel forward-flyback converter is made and debuged. Through experiments, the two clamp circuit already regular run in the converter, the highest efficiency of proposed new converter reach 94% and the difference between minimum and maximum input voltage is 240V. The experimental results show the correctness of the theoretical analysis, which demonstrate the new forward-flyback converter has the advantage of wide input range and high efficiency.