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In this paper, an active electromagnetic interference (EMI) choke for both common-mode (CM) and differential-mode (DM) noise suppression is proposed. Three isolated windings with a different number of turns are wound on the same magnetic core. One of the windings is served as the auxiliary winding connecting to an active circuit called the negative impedance circuit. The inductance of the EMI choke is substantially boosted up to effectively attenuate the low-frequency noise. This technique leads to a greater inductance but fewer turns and smaller size of the EMI choke. Different from the design of a conventional EMI filter, which uses separated CM and DM chokes, this proposal saves the cost and space of the EMI filter. The enhancement to the CM and DM impedance is individually analyzed and experimentally confirmed. Based on the classical CM and DM noise models, CM and DM noise insertion losses are predicted using computer simulation. The simulation results are validated by a network impedance analyzer. Finally, conducted EMI tests are carried out to verify the effectiveness of the proposed technique. [ABSTRACT FROM PUBLISHER]

Electronic products consist of parasitic capacitance between the circuit components and the ground, which introduces common mode (CM) noise. A CM inductor is used to block the noise following into the power supply affecting the others. However, the CM inductor and the parasitic capacitance could create resonance phenomenon that affect the filter performance in low frequency. In this paper, we investigate into this resonance phenomenon by giving a detailed analysis of the CM inductor and filter configuration. A three-winding CM inductor is then proposed to solve the aforementioned problem. This three-winding CM inductor consists of two traditional CM inductor winding and an auxiliary winding connecting to a negative impedance converter. The impedance of the CM inductor is virtually boosted up. Without physically increasing the value of the inductance, the noise attenuation in low frequency is improved and the resonance phenomenon is significantly mitigated. A prototype is constructed and practically tested on a 100-W switched-mode power supply. Experimental results show that the three-winding CM inductor operates as theoretically anticipated. The noise level at the resonant frequency is reduced by 21 dB, whereas the power consumption of the additional circuit only consumes 0.5 W. [ABSTRACT FROM AUTHOR]

This paper presents a power converter and its control circuit for high-frequency-fed ac to dc conversion. Based on the resonant technique, the input current is shaped to be sinusoidal and is forced to follow the high-frequency sinusoidal input voltage so as to achieve unity power factor. With the proper selection of the characteristic impedance of the resonant tank, the converter is able to perform the function of a buck, boost, or buck-boost converter. The initial condition of the resonant tank is used to control the output voltage gain of the converter. Since all the switches are operated at the fundamental frequency of the input ac source, the switching loss of the converter is small. A control scheme is also proposed for the converter. A proof-of-concept prototype operating at 400 kHz is constructed and its performance is experimentally measured. Results show that the proposed converter operates as theoretically anticipated. [ABSTRACT FROM AUTHOR]