JPH0452969Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a noise filter that prevents interference to telephones and data terminal equipment due to radio wave induction into telephone lines.

Conventionally, methods to prevent this type of radio wave induced interference have been used, such as inserting a capacitor between the line and earth to create a bypass, inserting an inductor to prevent the intrusion of interference waves, or using a combination of a capacitor and an inductor. However, when using a capacitor, there are drawbacks such as the difficulty of connecting to the ground and the fact that the earth wire acts as an antenna, reducing the prevention effect.

Furthermore, in the method of inserting an inductor into each line of the telephone line, the attenuation of the filter must be 20 dB or more, considering the characteristics of the telephone.
The impedance of the filter must be approximately 60 kΩ at 1 MHz, and the inductance must be approximately 9.5 mH, which has the disadvantage of deteriorating transmission characteristics in the case of pulse transmission, and it is difficult to maintain balance between two telephone lines. Currently, sufficient effects cannot be obtained due to the following reasons.

The equivalent circuit for common mode noise when an inductor with an inductance L is inserted into each line is shown in FIG. 1, and the impedance of the chiyoke coil is jωL/2.

On the other hand, there is a method to eliminate noise by inserting a common mode choke coil into the line.

Broadcast waves guided into a telephone line under a strong electric field, for example near a broadcasting tower, are coupled between each line of the line and the ground. To eliminate these broadcast waves, the attenuation of the chiyoke coil must be approximately 20 dB due to the characteristics of the telephone. The capacitance between the phone and ground is approximately 40pF.

Since the Chi-Yoke coil is inserted in series in the coupling circuit, the impedance required for the Chi-Yoke coil can be obtained from the following equation. That is, the formula expressing the amount of attenuation due to inserting the Chi-Yoke coil into the coupling circuit is A=20log {Zl/(Zl+Zf)} A: Attenuation Zl: Load impedance Zf: Find Zf from the impedance of the Chi-Yoke coil.
However, this impedance is related to frequency, and the required impedance differs depending on the interference frequency.

FIG. 2 shows an equivalent circuit for common mode noise when a common mode chiyoke coil is used as the chiyoke coil. The impedance of the chiyoke coil is (jωL/2+jωM/2)/2. When the coupling coefficient is 1, since L=M, the impedance becomes jωL/2. In other words, the inductance of the common mode choke coil is 1/1 compared to the case where two inductors are used, as shown in Figure 1.
2 is fine.

Further, FIG. 3 shows an equivalent circuit for signals when a common mode chiyoke coil is used as the chiyoke coil. The impedance of the chiyoke coil is jωL−jωM+jωL−jωM. When the coupling coefficient is 1, since L=M, the impedance becomes 0. That is, the common mode choke coil does not affect the signal.

As mentioned above, the common mode filter has great features as a noise prevention filter that has never existed before.

However, in order to obtain an impedance of 30 kΩ or more in the medium wave band as described above, conventionally, only a common mode choke using a ring-shaped core has been considered.

The present invention aims to provide a chiyoke coil using a core of a new shape in order to realize cost reduction.

This invention is a drum-shaped inductor with an outer diameter of 15 mm or less, a length of 12 mm or less, and an annular groove on the outer periphery. This is a chiyoke coil for preventing induced noise in a telephone line, characterized in that it is constructed by bifilar winding a winding wire in a groove of a ferrite magnetic core.

An embodiment of the present invention will be described below with reference to the drawings.

Referring to FIG. 4, the inductor for a common mode choke according to the present invention has a magnet wire 2 wound around a drum core 1 in a bifilar manner, and the dimensions of the drum core are particularly important in obtaining the characteristics.

For example, as is clear from FIG. 5, the shaft diameter a is
The thinner the coil, the higher the inductance and the smaller the capacitance, and the thinner the coil, the better the conditions for a common yoke coil. Considering the drum core, 3mm.
The following is not practical. Therefore, 3 mm or more is required. As is clear from FIG. 6, the shorter the axial length b, the higher the inductance and the smaller the capacitance. Therefore, it is desirable to shorten the axial length b, but since the number of turns of the coil is required to obtain high impedance, the axial length b needs to be 3 to 4 mm considering the wire diameter of the winding. . The collar diameter c is the seventh
As is clear from the figure, the larger the inductance, the higher the inductance, so taking into consideration the strength of the drum core and the dimensions of the rosette, a length of about 12 to 15 mm is required.

The wire must be able to withstand a maximum current of 100mA, and is approximately 0.12φ and is made of polyurethane copper wire.

As is clear from Figure 8, the magnetic permeability μ of the magnetic core is
A magnetic permeability range of 240 to 650 has little effect on properties. Therefore, there is no need to worry about magnetic permeability.

In addition, considering the size of the telephone rosette,
The drum core should have a flange diameter of 15φ or less and a total length of 12mm or less.

Currently, the shaft diameter is 3.5φ, the shaft length is 3mm, the collar diameter is 14φ, and the wire rod
Figure 9 shows the impedance characteristics of a common mode yoke in which polyurethane copper wire is bifilar-wound around a 0.12φ drum coil.

By using such a common mode choke, an impedance of 30 kΩ or more can be easily obtained in the medium wave band.

Therefore, the Chiyoke coil of the present invention has an impedance of 30 kΩ or more to remove noise induced in the telephone line in the medium wave band, that is, the frequency band of 0.5 MHz to 1.5 MHz. can.

Also, compared to a ring core, the number of turns is large, but automatic winding is possible, and compared to a ring core, an inexpensive iron core can be used without limiting the material of the magnetic core, so it has many advantages in terms of manufacturing costs.

Note that this embodiment is not limited to only medium wave bands, and can be applied to high frequency bands by adjusting the number of turns.

[Brief explanation of the drawing]

Figure 1 shows the noise coupling equivalent circuit when an inductor is inserted into each telephone line, Figure 2 shows the noise coupling equivalent circuit of a common mode choke coil, and Figure 3 shows the equivalent circuit of a common mode choke coil for signals. Figure 4a is a perspective view of one embodiment of the present invention, Figure 4b is its equivalent circuit diagram, Figure 5 is a diagram showing the relationship between the shaft diameter of the drum core and the frequency characteristics of impedance, and Figure 6 is the drum core. Figure 7 is a diagram showing the relationship between the axial length of the drum core and impedance frequency characteristics, Figure 8 is a diagram showing the relationship between the magnetic permeability of the iron core and the frequency characteristics of impedance, Figure 7 is a diagram showing the relationship between the drum core collar diameter and impedance, FIG. 9 is a diagram showing the relationship between the number of turns and the frequency characteristics of impedance. a...Brim diameter, b...Shaft length, c...Shaft diameter, 1...
...Ferrite iron core, 2...Polyurethane copper wire.

Claims (1)

[Scope of utility model registration request] In a chiyoke coil that prevents radio interference induced in telephone lines to which telephones and data communication equipment are connected, the inductor of the chiyoke coil has a center core diameter of 4 mm, an outer diameter of 15 mm or less, a length of 12 mm or less, and an annular groove on the outer periphery. Consisting of a drum-shaped ferrite magnetic core, a winding is bifilar-wound in the groove,
A chiyoke coil for preventing induced noise in telephone lines, characterized by having an impedance of 30 kΩ or more in the frequency band of 0.5 MHz to 1.5 MHz.