Design and Research of a Low Loss Start High Voltage Wide Range Flyback Converter

With the rapid development of multi electric/all electric aircraft, active phased arrays, and fuel cells, the range of bus voltage is constantly increasing, and the power level is constantly increasing. At the same time, safety and conversion efficiency need to be considered. The number of isolation channels in the main conversion topology increases, and the parallel connection of multiple switching tubes brings greater power, wider input voltage range, and higher efficiency requirements to the auxiliary power source. To address this issue, research on the design of high-voltage wide range flyback converters is carried out. Firstly, the working mode and timing of the flyback converter are analyzed, and the expression of the output voltage gain of the converter under different modes is derived. Under extreme input conditions, a flyback transformer is designed based on the electromagnetic induction law and the Ampere loop law, where the transformer turn ratio is derived through the critical conduction mode; Secondly, small signal modeling is performed on the flyback converter and the transfer function is derived, followed by loop supplementary design based on the transfer function; Analyze the conventional RC startup circuit losses of the flyback converter and propose a low loss startup circuit that can switch to low loss mode after startup, further improving system efficiency; Finally, based on the analysis of the working principle and characteristics of the proposed converter, a 180-425V input, 5V output, 20$W$ experimental prototype was designed, with an external size of 1/16 brick. The correctness of the theoretical analysis and the feasibility of the scheme were verified.