JPH0514491Y2 - - 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, to prevent this type of radio wave induced interference, methods have been used: bypassing the line by inserting a capacitor between the line and the ground, inserting an inductor to prevent interference waves from entering, or using a combination of a capacitor and inductor. It had been. However, when using a capacitor, there are drawbacks such as the difficulty of connecting it to the ground and the fact that the ground wire becomes 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 should be about 60kΩ at 1MHz, and the inductance should be about 9.5mH, which has the disadvantage of deteriorating the transmission characteristics in the case of pulse transmission, and it is difficult to balance the two wires of the telephone. The current situation is that sufficient effects cannot be obtained for various 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. In other words, the formula that expresses the amount of attenuation caused by inserting a chiyoke coil into the coupling circuit is A=20log(Z/Z+Z) A: Attenuation Z: Load impedance Z:
Find Z from the impedance of the chiyoke coil. However, this impedance is a function of 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.

Therefore, in order to eliminate radio wave induced interference waves to the telephone line, it is preferable to insert a common mode choke in the middle of the telephone line.

By the way, as a method for connecting such a common mode choke coil in the middle of a telephone line, conventionally, two rosettes were used and the common mode choke coil was arranged and connected between the two rosettes.
In this case, there were disadvantages such as the necessity of using two rosettes and the fact that the common mode choke was exposed in the middle of the telephone line, which could be dangerous or cause a connection failure.

An object of the present invention is to provide a wideband and easy-to-mount chain coil that can be housed in a rosette while using a common mode chain coil.

The present invention mounts a common mode chiyoke coil on a board, provides a plurality of metal terminals on the board according to the number of lead wires of the common mode chiyoke coil, and connects the metal terminals to the common mode chiyoke coil. This is a choke coil for preventing induced noise in a telephone line, characterized in that it is electrically connected to a lead wire and can be housed in a telephone line rosette.

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

As shown in FIG. 4, a chiyoke coil made of a common winding of magnet wire 2 around a drum core 1 is mounted on a substrate 3, and a terminal 5 for electrical connection with the lead wire of the chiyoke coil is provided on the board 3. . The substrate 3 and the chiyoke coil are covered with a resin 4.

To give a specific example, the core outer diameter is 14φ, the shaft diameter
3.5φ, groove width 3mm, brim thickness 2mm, total length 7mm, material ferrite, magnetic permeability 400 drum core, 320 turns of polyurethane copper wire 0.12φ1 type, common winding chiyoke coil, 1mm thick, length and width 11.5 x 39
Glued to a mm glass epoxy substrate. On the board
Horseshoe-shaped 0.5mm thick fixed with 3φ screws,
Four Ni-3 plated brass terminals measuring 9 x 6.2 mm in length and width and 3 mm in height were provided and electrically connected to the lead wires of the chiyoke coil.

The Chiyoke coil and the board were painted with a thickness of 0.4mm. The common mode choke coil constructed as described above was able to obtain approximately 20 dB of attenuation in the medium wave broadcast wave band with one element. Moreover, as shown in FIG. 5, it can be stored in a mini-fax closet. In addition, in FIG. 5, 7 is a screw for an interrupted terminal. Moreover, the frequency impedance characteristics were as shown in FIG.

According to the present invention, it is possible to incorporate a common mode choke in a rosette for equipment that malfunctions due to broadcast waves guided into telephone lines, etc., and the implementation can be facilitated.

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

[Brief explanation of drawings]

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. FIG. 4 shows an embodiment of the rosette mounting rosette coil, with FIG. 4A showing a front view and FIG. 4B showing a partially cutaway side view. FIG. 5 is a plan view of a rosette mounted with a choke coil, and FIG. 6 is a diagram showing the characteristics of one embodiment. DESCRIPTION OF SYMBOLS 1... Fillite iron core, 2... Polyurethane copper wire, 3... Board, 4... Resin, 5... Terminal, 6...
...Rosette, 7...Screw for relay terminal.

Claims (1)

[Scope of utility model registration request] A common mode chiyoke coil is mounted on a board for mounting the common mode chiyoke coil, and a plurality of approximately horseshoe-shaped metal terminals are provided on the board according to the number of lead wires of the common mode chiyoke coil. The terminal is electrically connected to the lead wire of the common mode chain coil so that it can be stored in a telephone line rosette that has a relay terminal that can be connected to the metal terminal with a screw, and the terminal is electrically connected to the lead wire of the common mode cable. A Chi-yoke coil that prevents induced noise in telephone lines is characterized by a Chi-yoke coil covered with resin.