NIPPON CHEMI-CON CORPORATION

Replacing electrical characteristics equivalent to those of the ferrite choke coil specifications with the nanocrystalline coil FL-V series, offers the advantages of "downsizing", "low DCR" and "low stray capacitance".
In this article, we will introduce the superiority of the nanocrystalline coil FL-V series over ferrite choke coils, compared in the following items.

Compared criteria

• Impedance frequency characteristics
• Common Mode Filter - Noise Attenuation Characteristics
  The circuit configuration is comprised of a common mode filter within an LC noise filter effect (common mode) using common mode choke coils.
• Others, electrical characteristics, coil size, etc

Comparison parameters

We evaluate the advantages of replacing ferrite choke coils with FL-V coils with the following two items as common conditions for both FL-V coils and ferrite choke coils.

1. Impedance: Make the impedance roughly equal between 100kHz and 500kHz. For this coil specification, we use roughly 2.6kΩ/250kHz.
2. Copper wire: The wire material is common and the copper wire diameter is roughly the same.

Application	Common mode noise suppression for large currents
Ferrite core	General Mn-Zn ferrite (relative permeability equivalent to 5,000)
Rating Current	20A
Impedance	2.6kΩ (250kHz)
D.C.R. of copper wire	4.0mΩ/per coil
Stray capacitance C(Generation between copper wires due to winding)	13pF
Coil volume	64cm3 (Core size: 47mm, includes core case)

Replacing electrical characteristics equivalent to the above ferrite choke coils specifications with FL-V coils has the following advantages.

• Coil size downsizing → Mounting area, space reduction, weight reduction
• Low DCR → Reduced DC loss, low heat generation
• Low stray capacitance → Broadband noise elimination band

Below, the reasons for this are explained.

1. Specification comparison between ferrite choke coils and FL-V coils

If the FL-V coil satisfies the compared criteria, the coil size can be downsized, which contributes to reducing of coil mounting space.
Below is a table showing a comparison of external dimensions and the effect of replacing with the FL-V coil, including electrical characteristics.

Ferrite choke coils specifications	Our FL-V coil specifications
Outer diameter of core used: 47mm (In core case) Winding wire: ⌀1.6mm×2 parallel	Outer diameter of core used: 28mm (In core case) Winding wire: ⌀1.5mm××2 parallel

Comparison items	Ferrite choke coils	Our FL-V coil	Effects of replacing ferrite choke coils
Core volume[cm3]	17.1	4.9	71% improvement, coil downsizing, contributes to weight reduction.
Coil volume[cm3]	64.1	29.5	54% improvement, coil mounting space reduced. (Note 1)
Coil weight[g]	160.0	73.0	54% improvement, coil mounting equipment weight reduced.
DCR[mΩ]	4.0	2.4	40% improvement, DC loss reduced. Low heat emission.
Stray capacitance[pF]	13.0	8.0	38% improvement, improved high frequency side noise elimination.

Remark 1:

Impedance is common for both ferrite choke coils and FL-V coils at approximately 2.6kΩ±10%/approximately 250kHz.

Remark 2:

Coil volume does not include the space inside the coil.

Remark 3:

DCR is the copper wire resistance value per coil.

Note 1:

With coil volume, the smaller the core size used, the smaller the volume difference between ferrite choke coils and FL-V coils.
This is because the copper wire diameter and core case thickness have a greater impact on the small core size. Also, there are concerns about heat dissipation properties.

2. Impedance comparison between ferrite choke coils and FL-V coils

Next, we compared the impedance frequency characteristics of the ferrite choke coils and the FL-V coils that satisfy the comparison conditions. We created a simple common mode filter and measured the noise attenuation characteristics when using the ferrite choke coils and the FL-V coils.

Figure 1 represents an image of the difference in impedance characteristics between ferrite choke coils and nanocrystalline coils (our FL-V series).
Based on the comparison conditions, set an equivalent impedance of roughly 250kHz for frequency point A. Here, there are the following two characteristics of our FL-V coils compared to ferrite choke coils.

• Improvement to low-frequency band impedance in band ①
  →FL-V coils have a higher relative permeability than ferrite choke coils, and high impedance can be obtained with a small number of windings.
• Improvement to high-frequency band impedance in band ③
  →By reducing the number of windings, the stray capacitance (capacitance between windings) is reduced, and the resonance point can be extended to the frequency point B point (approximately 1 MHz to several MHz) compared to ferrite choke coils.
  （For an explanation of capacitance between windings, refer to 1. Effects of stray capacitance in Common Mode Choke Coils, Frequency Characteristics of Common Mode Choke Coils.）

Ferrite choke coils have a lower permeability ratio than FL-V coils, and obtaining a high impedance requires increasing the number of windings. However, increasing the number of windings invites a decline in resonance frequency and a decline in impedance on the high-frequency side. When trying to obtain high impedance with ferrite choke coils, the band in which high impedance can be maintained becomes narrower than with FL-V coils, and resonance peaks tend to occur at relatively low frequencies.

In summary, if the characteristics of Band ② are equivalent to those for ferrite choke coils, then FL-V coils can maintain a higher impedance than ferrite choke coils over the wide band of Bands ① and ③. The use of the FL-V coil can be expected to improve the noise suppression capability over a wide band.

3. Comparison of simple common mode filter characteristics of ferrite choke coils and FL-V coils

In the above circuit configuration, capacitor Y (Cy) is ceramic capacitor 0.5μF. Also, the noise attenuation is assumed to be around -60dB at approximately 100kHz, and the cutoff frequency fc will be 3kHz to 4kHz.

Remark 1:

The 2.5MHz resonance point depends on the frequency characteristics of C_y (ceramic capacitor).

Remark 2:

Filter attenuation after the 2.5MHz resonance point is affected by the impedance drop due to the coil winding capacity as well as the inductance component of C_y.

Remark 3:

High-frequency side characteristics are max 40MHz due to the accuracy of the measurement instrument.

From Figure 2, we see that attenuation characteristics are -50 to -60dB at 100kHz for common mode filters using ferrite choke coils and our FL-V coils, which is roughly according to designs. In addition, from the impedance characteristics in Figure 1 and the filter characteristics in Figure 2, the use of the FL-V coil improves the noise attenuation characteristics in the low frequency band from 3 kHz to 200 kHz and the high frequency band above 1 MHz, meaning that further coil downsizing and weight reduction can be achieved.

Conclusion

In this document, we evaluated the following about our FL-V series coils and common mode coils made of ferrite.

• Impedance comparison (0utline)
• Common mode filter comparison

In this article, we evaluated coil specifications limited to a focus on applications for large currents. When considering common mode filter designs in the future, we hope you will consider our FL-V series coils.