Abstract: A quasi-resonant Flyback（QR-Flyback）converter with 65 W output was designed. The valley

switching principle and the switching loss reduction mechanism of QR-Flyback were analyzed，the frequency and

loss characteristics of the system under different working conditions were compared，and the advantages and

disadvantages of frequency conversion control were summarized. Combined with the frequency hopping control

function of the NCP1380 controller，the hardware circuit parameters of each part of the system were designed and

the efficiency of the system was effectively improved. Finally，the feasibility of theoretical analysis and parameter

design were verified by simulation and experiment.

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      Key words: quasi-resonant Flyback（QR-Flyback）；valley switching；frequency hopping control