Duty Cycle Loss Compensation Method Based on Magnetic Flux Cancelation in High-Current High-Frequency Synchronous Rectifier of LCLC Converter

With uncertainty of the parasitic parameter in different practical layout, two synchronous rectifiers (SR) with same topology and identical components may exhibit significant difference in driving timing and each SR FET may suffers from the duty cycle loss. In this article, the mutual induction between the voltage detection network of SR controller and the transformer secondary windings is first investigated. Then, a compensation method based on magnetic flux cancellation is proposed to solve the duty cycle loss issue caused by the parasitic inductive coupling, which enables further increase of switching mode power supply efficiency. With the proposed compensation method, only an additional wire turn is required with no need to change the layout, resulting in reducing the difficulty for implementation in practical prototypes. Where, a most compatible method is employed after multiparameter extraction methods comparison and the parasitic parameters are given out. Then, the design process of a specific compensator is proposed. Finally, a prototype of 400 to 14 V, 1.5 kW LCLC resonant converter was employed to verify the advantages of the proposed method. An efficiency improvement of 0.8% is achieved. The method can be generally applied to different kinds of SR controllers. This article is accompanied by a video demonstrating operation waveforms.

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