A lumped-element circuit model of ferrite chokes

Abstract

An RLC model of ferrite chokes for suppressing common-mode (CM) currents is presented. The equivalent lumped-element circuit parameters are obtained from the frequency-dependent input impedance of a ferrite choke on a wire above the ground plane. This input impedance can be either measured (using vector network analyzer or impedance analyzer), or numerically modeled based on the known ferrite material properties (permittivity and permeability). An example of using both numerical modeling and measurements is provided. Results show good agreement at comparatively low frequencies (below 200 MHz). The upper frequency limit for the proposed equivalent lumped-circuit model is discussed.

Performance Study of Split Ferrite Cores Designed for EMI Suppression on Cables

“…where H is the core's height and OD and ID are the outer and inner diameter, respectively. The overall reluctance of the split-core considering the air gap can be calculated from (1) as the sum of the reluctance core (R c ) and reluctance air gap (R g ) [13,15]:…”

“…EMI suppressors, such as cable ferrites, are usually classified by the impedance that they can introduce in a specific frequency range when they embrace a conductor. This parameter represents the magnitude of the impedance that can be represented from a series equivalent circuit mainly based on a resistive and inductive component [13,20]. The resistive component is connected to the imaginary part of the relative permeability representing the core's losses, whereas the real part of the permeability is related to the inductive component [22].…”

“…Nevertheless, these drawbacks are usually compensated by the effectiveness of cable ferrites to filter interferences without having to redesign the electronic circuit [6,7]. Manufacturers provide a wide range of ferrite cores with different shapes, dimensions and compositions, but the most widely used solutions applied to cables are the sleeve (or tube) ferrite cores or their split variation, the openable core clamp (or snap ferrites) [13]. This component is manufactured from two split parts pressed together by a snap-on mechanism, turning this into a quick, easy to install solution for reducing post-cable assembly EMI problems.…”

“…Another difference between NiZn and MnZn traces is observed by comparing the g0 traces because the initial permeability decreases mostly in MnZn because the original non-split-core yields a higher initial permeability than the NiZn sample. The estimation of g0 traces was obtained by fixing a gap of 0.01 mm between both split parts in order to simulate the real snap ferrite's behavior, and the estimated values match with the experimental data [13]. The NC graph shows a different behavior than the ceramic core since the experimental and calculated permeability only matches in the low-frequency region.…”

Common-Mode Impedance of a Ferrite Toroid on a Cable Harness

“…The approach in [11][12][13] for toroids may be modified and applied to a ferrite toroid on a wire, but only at low frequencies. This was done in [14], where the frequency range was limited to about 200 MHz. No traveling-wave effects were taken into account, however, which limited the applicable frequency range of the published models.…”