Investigating Switching Transformers for Common Mode EMI Reduction to Remove Common Mode EMI Filters and Y-Capacitors in Flyback Converters

Li, Yiming; Zhang, Huan; Wang, Shuo; Sheng, Honggang; Chng, Choon Ping; Lakshmikanthan, Srikanth

doi:10.1109/jestpe.2018.2827041

Cited by 64 publications

(31 citation statements)

References 21 publications

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“…Based on this consideration, transformer evaluation methods have been proposed in previous papers. Reference [22] proposed that only a signal generator and an oscilloscope can achieve transformer evaluation. However, this method is not accurate enough limited by the accuracy of the test equipment.…”

Section: Evaluation Methods a Traditional Evaluation Methodsmentioning

confidence: 99%

“…This paper will use network analyzer to evaluate the transformer and the equivalent capacitance is deduced based on S 21 . Besides, the evaluation method in [21] and [22] both need the prototype to evaluate. S 21 can not only be measured but also be simulated by FEM simulation tool.…”

Section: Evaluation Methods a Traditional Evaluation Methodsmentioning

confidence: 99%

“…By (22), it can find that the CM charges moving through the transformer are Q ps + Q sp − Q cs determined by V P .C Q , and C Q is a lumped CM noise capacitance in transformer coupling path. The CM charges in other conduction path are Q pg determined by V P .C X .…”

Section: CM Noise Reduction Techniquementioning

confidence: 99%

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Evaluation Method of Flyback Converter Behaviors on Common-Mode Noise

Chen

2019

IEEE Access

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Common-mode (CM) conduction electromagnetic interference (EMI) is a challenge for switched-mode power supply (SMPS) designers. A flyback converter is a traditional topology used in low-power isolated applications. The size and cost of EMI filters are important considerations for higher power density and lower cost of SMPS design. In most cases, the CM current is generated by voltage pulsation (dv/dt) assigned on the primary winding and the secondary winding. The CM current conduction paths can be mainly categorized into two categories. One is the interwinding parasitic capacitance of the transformer, and the other is the parasitic capacitance between the semiconductor switches and the protective ground. This paper proposed an evaluation method to measure the equivalent CM noise capacitance of the two main CM current conduction paths, respectively. Then, this paper proposed a CM noise cancellation scheme based on the transformer winding design combining the measurement technique and the FEM simulation tool. Planar transformers with PCB windings also have advantages in low profile, good heat dissipation, and good stray parameter consistency. Based on these considerations, an 18-W adapter is designed and tested to verify the effectiveness of the proposed evaluation method and the design scheme. INDEX TERMS Common-mode (CM), flyback, EMI, planar transformer, equivalent capacitance.

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Section: Evaluation Methods a Traditional Evaluation Methodsmentioning

confidence: 99%

Section: Evaluation Methods a Traditional Evaluation Methodsmentioning

confidence: 99%

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Evaluation Method of Flyback Converter Behaviors on Common-Mode Noise

Chen

2019

IEEE Access

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“…Many previous references also have discussed the issue on how to evaluate the CM noise behavior of the transformer [17][18][19][20]. Figure 5a,b depicts the traditional transformer CM characteristic evaluation method.…”

Section: Previous Evaluation Methodsmentioning

confidence: 99%

“…In Section 5.1, three kinds of transformers have been evaluated based on the proposed evaluation method. In this section, the following will use the previous method proposed in [18] to compare the difference between these two methods. Figure 17 shows the measurement results of the insertion loss of 1#, 2#, and 3# transformers.…”

Section: Cq Verificationmentioning

confidence: 99%

A General Transformer Evaluation Method for Common-Mode Noise Behavior

Chen

Lin

2019

Energies

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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.

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An asymmetrical cancellation method for common mode voltage in full‐bridge LLC converter utilizing nonideal transformer

Liu,

He,

et al. 2024

Circuit Theory & Apps

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This paper proposes a common mode voltage (CMV) reduction method for power full‐bridge LLC converter. A detailed derivation of asymmetrical CMV source in energy transmission (ET) and dead time resonance (DR) is presented, and a common mode (CM) equivalent circuit model considering stray parameters of power devices and transformer for the high‐voltage power LLC converter is constructed. This study assesses the influence of asymmetric junction capacitances of power devices and stray capacitances of transformer on both the CMV source and the CM model. It also examines the impact of power level on the constituent elements of the CMV source. Additionally, a theory of asymmetric CMV source cancellation is deduced based on the nonideal power LLC converter, where asymmetric noise source and coupling pathway are taken into account, which helps mitigate it through matching circuit structure without extra components. Finally, a 30 kHz 2 × 50 kW prototype is constructed and validated to reduce the CMV where the experiments show that the output CMV within high‐frequency band could be reduced by 12.15 dB at rated operating conditions.

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Investigating Switching Transformers for Common Mode EMI Reduction to Remove Common Mode EMI Filters and Y-Capacitors in Flyback Converters

Cited by 64 publications

References 21 publications

Evaluation Method of Flyback Converter Behaviors on Common-Mode Noise

Evaluation Method of Flyback Converter Behaviors on Common-Mode Noise

A General Transformer Evaluation Method for Common-Mode Noise Behavior

An asymmetrical cancellation method for common mode voltage in full‐bridge LLC converter utilizing nonideal transformer

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