Conducted EMI mitigation schemes in isolated switching-mode power supply without the need of a Y-capacitor

In order to construct a low-impedance loop for common-mode electromagnetic interference (EMI) signals, traditional method is to use Y-capacitors as filtering components. However, in the commonly used isolated ac-dc switching-mode power supplies (SMPS), the Y-capacitors branch also behaves as a terrible leakage current loop. For the safety of human beings, this leakage current is not allowed in commercial used equipment, such as chargers, medical instruments, etc. Therefore, certain works should be done to both acquire good EMI performance and satisfy the strict leakage current limitation. The goal of this paper is try to meet these two demands at the same time. In this paper, a novel non-Y-capacitor EMI design concept for SMPS is proposed for the first time. By getting rid of traditional EMI filtering component - the Y-capacitors, the leakage current can be eliminated entirely. Meanwhile, to face with EMI design challenge, optimized transformer architecture is presented. Analysis of the transformer architecture as well as the auxiliary winding has been carried out. Then, a novel topology suitable for non-Y-capacitors converter is proposed and the design procedure of the proposed topology is discussed in detail. The proposed concept is applied to several popular converter topologies. The experiment results demonstrated the effectiveness and feasibility of the proposed non-Y-capacitor design schemes.