A General Transformer Evaluation Method for Common-Mode Noise Behavior

Abstract

In isolated power converters, the transformer is a key part of voltage transformation and isolation. Since common-mode (CM) noise is rather difficult to suppress compared with different-mode (DM) noise, more and more scholars are paying attention to the characteristics of CM noise, especially in high-frequency CM noise behaviors. CM noise can be further divided into conducted CM noise and radiated CM noise, and the main focus of this paper is on conducted CM noise. The CM coupling capacitance of the transformer is one of the main contributors of CM noise, which has been verified in many previous studies. Hence, eliminating the CM noise in a transformer coupling path can significantly lower the whole CM noise level of the converter. Professional conducted electromagnetic interference (EMI) testing instruments are quite expensive. In this paper, a general transformer evaluation technique for CM noise behavior is proposed. Only a signal generator and oscilloscope can achieve transformer CM noise behavior evaluation. PCB planar flyback transformers are designed, and a series of noise spectrums and voltage waveforms can verify the effectiveness of the proposed transformer evaluation method. The flyback adapter porotype can pass the EMI standard limited line EN55022 class B by the proposed evaluation method.

Grounding and Isolation Requirements in DC Microgrids: Overview and Critical Analysis

“…In the case of high-frequency isolation, the important point is the existence of a stray parasitic capacitor between the primary and secondary of the high-frequency transformer C iW (interwinding capacitor). In different studies, different methods have been presented to model this capacitor, which is in the picofarad range [67,68]. Stray capacitors in parallel to insulation resistance are used here for a high-frequency transformer.…”

Modeling and Suppression of Conducted Interference in Flyback Power Supplies Based on GaN Devices

“…Reference [16] utilized core shielding to address the coupling problem caused by the transformer core and employed a converter to solve the issues of multi-Y capacitance and capacitive filtering, providing better EMI suppression compared to conventional pulse-width modulation. Reference [17] highlighted the significant influence of transformer common-mode coupling capacitance on noise suppression and demonstrated that the feasibility of the transformer can be verified without an EMI receiver, using only a signal generator and an oscilloscope. References [18][19][20] incorporated balanced winding techniques to achieve effective shielding and offset common-mode noise, and they provided a theoretical method for calculating the number of turns in a balanced winding, which is valuable for this study.…”