NIPPON CHEMI-CON CORPORATION

Common Mode Coil Impedance Characteristics and Overview of the Equivalent Circuit

In Figure 1, as shown by the blue line, ideal impedance characteristics increase in proportion to frequency.
However, in reality, impedance characteristics are as shown by the red dotted line due to loss caused by eddy current loss generated in the core and impedance drop caused by inter-winding capacitance.
Here, the characteristics of the red dotted line can be expressed by the parallel circuit of Lo, R, and C in Fig. 1. Lo expresses the common mode inductance, R the loss due to eddy current with resistance, and C the interwinding capacitance.
Furthermore, following the characteristics of the red dotted line, Lo, R, and C form an impedance characteristic with Lo on the low frequency side, R on the middle band, and C on the high frequency side.
However, the intermediate band represented by R is actually frequency-dependent, and the resistance R alone causes a difference from the actual measurement.
The equivalent circuit based on Lo, R, and C in Fig. 1 is referred to as the conventional model, and the equivalent circuit with an improved expression of R is adopted as a detailed model in the SPICE MODEL of the FL-V series, which is explained below.

Features of FW,FL-V series SPICE MODEL

As shown in Fig. 2, the SPICE MODEL of the FW,FL-V series is a detailed model with improved impedance reproducibility in the band where the resistance component R in the impedance characteristics is dominant compared to the conventional model (currently being applied to two of our FL series products).
The reproducibility of impedance characteristics in the resistive component dominant band has been improved by making R of the conventional model shown in Fig. 3 into a ladder structure using R and L as shown by the R’ in the detailed model in Fig. 4.
In the R-dominant band, there is actually frequency dependence, and R’ is introduced to reproduce this frequency dependence.

How the above detailed model was introduced to the FW,FL-V series

The background behind the adoption of the detailed model lies in the difference in impedance between the FL series and the FW,FL-V series in the resistive component dominant band.
The FW,FL-V series has a higher impedance increase rate in this resistance component dominant band compared to the FL series, and the conventional model adopted for the FL series has worse impedance reproducibility compared to the FW,FL-V series.
Therefore, in the FW,FL-V series, we introduced a detailed model to improve the reproducibility in the resistance component dominant band.

Precautions for using the FW,FL-V series SPICE MODEL

• The simulation reproducibility bandwidth is about 30MHz.
• This SPICE MODEL has been verified to work with OrCAD 9.2 Lite Edition and OrCAD Capture CIS-Lite version 17.2.
• Fig. 2 shows the measured impedance values ​​and simulation for a vertically placed product.
• Because this SPICE MODEL is constructed from samples with standard characteristics, there may be discrepancies between simulations using this SPICE MODEL and actual measurements, depending on the product standard.

Notes concerning the use of this document

• This document is reference data for the characteristics of the product and does not guarantee the characteristics of the product.
• To ensure correct and safe product use, do not rely on this document and, instead, make judgment after mounting the product and conducting tests.
• This document may be supplemented, revised, or modified without prior notice for improvement or other reasons.
• Please note that Nippon Chemi-Con Corporation will not be held responsible for any damages resulting from the use of this document.
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• Please refrain from redistributing or reprinting this document.