Experimental Investigation of the Dimensional Effect on Small-Signal Characteristics of Common-Mode Inductors

Abstract

Due to their high permeability and high effective permittivity, manganese zinc (MnZn) ferrites exhibit magnetic resonance depending on the core dimension. Once magnetic resonance occurs, the relative permeability of MnZn ferrites decreases drastically in the high-frequency (HF) range. The decrease in the relative permeability can influence the HF noise reduction performance of common-mode inductors (CMIs). Based on the above, this study experimentally investigates the impact of the dimensional effect of MnZn ferrites on the small-signal characteristics of CMIs. First, the CM small-signal characteristics of CMIs with different core dimensions indicated that the dimensional effect of MnZn ferrites decreases the CM impedances of the CMIs in the HF range. Two types of core division (air gap insertion and core lamination) were applied to the core to mitigate the dimensional effect on the CM impedances of the CMIs. The influence of the core divisions on the complex permeabilities and the small-signal characteristics of the CMIs were evaluated based on the experimental results. The measurement results clarified that core lamination might be the appropriate option in EMI filtering applications because it can mitigate the dimensional effect and increase the CM impedance of CMIs in the HF range without increasing the number of turns.

Keywords

• Common-mode inductors
• EMI
• MnZn ferrites
• permeability
• small-signal characteristic