Design and Analysis on Feedback Energy Loss of RCD Clamping Flyback Converters

The energy transfer process of the flyback converter with RCD clamp circuit was analyzed.It was concluded that the clamp voltage(UC) of the clamp capacitor must be higher than the feedback voltage(Uf) to avoid too much energy loss resulted from the feedback voltage providing energy to the RCD clamp circuit during the period of switch turn-off.The expression of the feedback energy(Wf) generated by the feedback voltage(Uf) was deduced.It was indicated that Wf decreases with the increment of UC,moreover,the total energy loss caused by the RCD clamp circuit is equal to the summation of Wf and Wlk,the energy from the leakage inductor.Let Wf?Wlk,the critical clamp voltage of the clamp capacitor,UCK?2.6Uf,can be obtained.On this basis,the design methods for the element parameters of the RCD clamp circuit were proposed.The validity of the theoretical analysis and the feasibility of the proposed design methods were verified with the simulation and experimental results.