JPH0411709A - Common mode choke coil - Google Patents

Abstract

PURPOSE:To reduce stray capacitance in series with a signal line and also eliminate floating capacitance in parallel with the line to effectively remote noise by providing coil conductors on a substrate sheet, laminating protective sheets on and under the sheet, and providing outer electrodes connected to both terminals of the coil conductors on the surface of the laminate. CONSTITUTION:Coil conductors 2, 3 are provided on a ferrite green sheet 1. The conductors 2, 3 are formed by screening by using conductive paste mainly containing Ag or Ag-Pd into an approximately U-shape while their surface sides are close to each other and parallel to a lengthwise direction of the sheet 1. Then ferrite green sheets 5, 6 to be protective sheets are laminated on and under the sheet 1, and after these are baked, outer electrodes 7a, 7b, 8a, 8b are formed on the four corners of the laminate by applying and bonding conductive paste wherein the electrodes 7a, 7b are connected to terminals 2a, 2b of the conductor 2 and the electrodes 8a, 8b are connected to terminals 3a, 3b of the conductor 3.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a common mode choke coil.

Conventional Technologies and Issues Conventionally, common mode choke coils shown in Figures 7 and 8 have been used to remove asymmetric component (common mode) noise that flows between the power line of electronic equipment and the ground. Ta. The choke coil shown in FIG. 7 has a primary winding 21 and a secondary winding 22 wound around a rectangular ferrite core 20 so that the windings do not overlap vertically. However, in this type, the stray capacitance Cs' between each line
occur in parallel. FIG. 8 shows a type with reduced stray capacitance, in which a primary winding 26 and a secondary winding 27 are bifilar-wound around a circular ferrite core 25.

However, even with this type, stray capacitance Cs'' occurs between each line depending on the winding state.

FIG. 6 shows an equivalent circuit of the conventional common mode choke coil, which has a problem in that high frequency common mode noise is bypassed due to stray capacitance Cs generated between the terminals.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a laminated common moat chiyoke coil that has a good noise removal effect and is compact and can be mounted on a surface.

In order to solve the above problems, the common mode choke coil according to the present invention includes a coil conductor provided on a substrate sheet,
A protective sheet is laminated on the upper surface of the substrate sheet, and external electrodes connected to both ends of the coil conductor are provided on the surface of the laminated body.

The coil conductor is provided on the substrate sheet in various forms so that common mode noise can be removed.

For example, as shown in Figure 1, one sheet may be arranged parallel to each other and close to each other, or two sheets each having one coil conductor may be arranged parallel to each other as shown in the 4th TyJ. Stack them so that they are close to each other.

Since the laminated common mode choke coil having the above structure is a sheet laminated type, it can be mounted at high density, and its equivalent circuit is as shown in FIG. The stray capacitance Cs between the terminals is extremely small, and the problem of bypassing high frequency common mode noise is solved.

In addition, stray capacitance Cp occurs between different poles, and this stray capacitance C
The symmetrical component (normal mode) noise superimposed on the load current and reciprocating between the power lines is removed by p.

Adoption! Embodiments of the common mode choke coil according to the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a first embodiment, in which coil conductors 2 and 3 are provided on the surface of a ferrite green sheet 1. The coil conductor 2.3 is formed by screen printing a conductive paste mainly composed of Ag or Ag-Pd, and extends in a substantially U-shape parallel to and close to, for example, the longitudinal direction of the sheet 1. .

An arbitrary number of ferrite green sheets on which electrodes are not formed on the upper and lower surfaces of the ferrite green sheet 1 (
Protective sheets) 5.6 are laminated.

In the actual mass production process, the sheets 1, 5 and 6 have a large area and are cut into units after lamination and pressure bonding and are fired. After firing, as shown in FIG. 2, external electrodes 7a, 7b, 8a, and 8b are provided at the four corners of the laminate by applying a conductive paste and baking to form a surface-mounted chip. The external electrodes 7a and 7b are the ends 2a of the coil conductor 2.
, 2b, and the external electrode 8g, 8b is connected to the coil conductor 3.
It is connected to the ends 3a and 3b of.

The common mode choke coil configured as above is
Unlike the conventional type shown in FIGS. 7 and 8, high-density surface mounting on a circuit board is possible. It also has an equivalent circuit shown in Figure 5. The coil conductors 2.3 are inserted in series between the power supply and the electronic device, respectively.
Removes common mode noise that commonly applies to

In this case, the stray capacitances Cs, Cs generated between the external electrodes 7a, 7b and 8a, 8b are extremely small, and there is no risk of high frequency noise bypassing. On the other hand, the external electrode 7a.

Stray capacitances CP and CP are also generated between 8a, 7b, and 8b, and this capacitance has the function of dissipating normal mode noise reciprocating between the coil conductors 2 and 3 to the ground line.

Note that the external electrodes 7a, 7b, 8a, and 8b can be provided in any desired form, for example, the form shown in FIG. 3 may be used.

FIG. 4 shows a second embodiment, in which a coil conductor 13.1 is arranged longitudinally in the center of the surface of a ferrite green sheet 11.12.
4. By stacking the sheets 11.12, the coil conductors 13.14 are arranged in parallel and close to each other, and an arbitrary number of protective sheets 15.16 can be stacked on the upper and lower surfaces of the sheets 11.12. This is similar to the first embodiment in that it is finished into a chip type by being cut and fired after lamination. The external electrodes are provided in the shape shown in FIG. 2 or 3, and can be connected to the ends 13a, 13b, 14g, and 14b of the coil conductor 13, 14 (7), respectively.

The equivalent circuit and noise removal effect are also the same as in the first embodiment.

Note that the common mode choke coil according to the present invention is not limited to the above-mentioned embodiments, and can be variously modified within the scope of the gist.

For example, the coil conductors 13 and 14 shown in the second embodiment are
It may be formed on the front and back sides of a single sheet. Furthermore, the green sheets 1.2.5.6.11.12, 15.16 may be made of not only a magnetic material but also a dielectric material, an insulator, or a mixture thereof.

Effects of the Invention As is clear from the above explanation, according to the present invention, a coil conductor is provided on a substrate sheet and laminated with a protective sheet, and an external electrode is provided on the laminated body, so that stray capacitance in series with the signal line is reduced. is extremely small, and a stray capacitance is generated in parallel with the signal line.As a chip component for noise countermeasures, it is effective in removing common mode noise and normal mode noise from low frequencies to high frequencies. Moreover,
Since it is a small and lightweight chip type, high-density surface mounting is possible. Furthermore, because it has a completely closed magnetic circuit structure, it will not adversely affect surrounding electronic components.

[Brief explanation of drawings]

Fig. 1 is an exploded perspective view showing a first embodiment of the present invention, Fig. 2 is a perspective view of a state in which the components shown in Fig. 1 are laminated and external electrodes are provided, and Fig. 3 is a perspective view showing another way to attach the external electrodes. is a perspective view showing the state. FIG. 4 is an exploded perspective view showing a second embodiment of the present invention. FIG. 5 is an equivalent circuit diagram of a choke coil according to the present invention. FIG. 6 is an equivalent circuit diagram of a conventional common mode choke coil. FIGS. 7 and 8 are perspective views showing conventional common mode choke coils, respectively. DESCRIPTION OF SYMBOLS 1... Ferrite green sheet, 2, 3... Coil conductor, 5, 6-... Protective sheet, 7a, 7b,
8a, 8b external electrode, 11.12... ferrite green sheet, 13, 14... coil conductor, 15
．． 16...Protection sheet. Patent applicant Murata Manufacturing Co., Ltd.

Claims (3)

[Claims] 1. A common mode choke characterized in that a coil conductor is provided on a substrate sheet, protective sheets are laminated on the upper and lower surfaces of the substrate sheet, and external electrodes connected to both ends of the coil conductor are provided on the surface of the laminate. coil. 2. 2. The common mode choke coil according to claim 1, wherein the pair of coil conductors are provided on one substrate sheet in parallel and close to each other. 3. 2. The common mode choke coil according to claim 1, wherein two substrate sheets provided with coil conductors are laminated so that each conductor is parallel and close to each other.