JPH08115820A - Common-mode choke coil - Google Patents

Abstract

PURPOSE: To provide a common-mode choke coil by which a normal-mode signal is passed and by which a common-mode noise is absorbed. CONSTITUTION: A common-mode choke coil 10 comprises input terminals 12a, 12b. Input terminals of a first choke coil 14a are connected to the input terminals 12a, 12b. The first choke coil 14a is used to pass a normal-mode signal and to cut off a common-mode noise. Output terminals the first choke coil 14a are connected to output terminals 22a, 22b. In addition, input terminals of a second choke coil 14b are connected to the input terminals 12a, 12b. The second choke coil 14b is used to cut off the normal-mode signal and to pass the common-mode noise. Output terminals of the second choke coil 14b are grounded via terminating resistors 24a, 24b. The terminating resistors 24a, 24b are used to convert the common-mode noise into heat so as to be consumed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a common mode choke coil, and more particularly to a normal mode signal passing through
The present invention relates to a common mode choke coil that blocks common mode noise.

[0002]

2. Description of the Related Art In a two-wire type transmission line such as a telephone line, a signal is in a normal mode and a noise is in a common mode. Therefore, a common mode choke coil is used in order to block common mode noise. Is used.

9 and 10 are illustrative views showing an example of a conventional common mode choke coil. This common mode choke coil 1 has two windings 3 on one core 2.
And 4 are applied. As shown in FIG. 9, the common mode choke coil 1 has a core 2 with two windings 3 and 4 for a normal mode signal.
The magnetic fields generated by the two windings 3 and 4 cancel each other and the magnetic fields generated in the core 2 by the two windings 3 and 4 are formed so as to be superimposed on each other, as shown in FIG. As a result, the common mode choke coil 1 acts as a choke coil for common mode noise, and cuts off common mode noise with a large impedance.

[0004]

However, when the common mode choke coil 1 has a high impedance with respect to the common mode noise, the transmission lines are in a mismatched state, and as shown in FIG. 11, the common mode noise is generated. It is reflected on the input side. Then, due to this reflection, a standing wave is generated in the transmission line on the input side, the transmission line on the input side acts as an antenna, and noise is radiated from the transmission line on the input side.

Similarly, as shown in FIG. 12, even in a balanced signal transmission line using two common mode choke coils 1, common mode noise is generated from the input side transmission line of each common mode choke coil 1. Will be emitted.

Conventionally, in order to suppress such noise radiation, the common mode choke coil is brought as close as possible to the noise generation source, or a part of the transmission line is covered with ferrite having a large loss. There are problems such as inconvenient placement of parts and lengthy equipment.

Therefore, a main object of the present invention is to provide a common mode choke coil which passes a normal mode signal and absorbs common mode noise.

[0008]

According to the present invention, there is provided an input terminal, and a first choke coil whose input end is connected to the input terminal and which passes a normal mode signal and blocks common mode noise. An output terminal connected to the output terminal of the first choke coil, and a second choke coil whose input terminal is connected to the input terminal for blocking normal mode signals and passing common mode noise. And the output end of the second choke coil is terminated via an impedance for consuming common mode noise.

In the common mode choke coil according to the present invention, the output end of the second choke coil may be terminated via a terminating resistor, for example.

[0010]

When a normal mode signal is input to the input terminal, the normal mode signal is cut off by the second choke coil, passes through the first choke coil, and is output from the output terminal. .

When common-mode noise is input to the input terminal, the common-mode noise is blocked by the first choke coil and passes through the second choke coil to, for example, a terminating resistor. Is consumed by the impedance of. Therefore, common mode noise is absorbed.

[0012]

According to the present invention, it is possible to obtain a common mode choke coil that passes a normal mode signal and absorbs common mode noise.

Further, in the common mode choke coil according to the present invention, since the common mode noise is absorbed, in order to suppress the emission of the common mode noise, it is brought as close as possible to the noise source or the loss is large. It is not necessary to cover a part of the transmission line with ferrite, and there are no problems such as inconvenient placement of parts or a large device.

The above-mentioned objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of the embodiments with reference to the drawings.

[0015]

1 is an illustrative view showing one embodiment of the present invention, and FIG. 2 is a circuit diagram thereof. This common mode choke coil 10 includes input terminals 12a and 12b.

The input terminals of the first choke coil 14a are connected to the input terminals 12a and 12b. The first choke coil 14a is for passing a normal mode signal and blocking common mode noise. The first choke coil 14a includes, for example, a ring-shaped core 16a, and the core 16a includes two windings 18a.
a and 20a are wound. In this case, the two windings 18
a and 20a, when a normal mode signal is input to one end of the core 1 by the two windings 18a and 20a.
The magnetic fields generated in 6a cancel each other and the two windings 18
When common mode noise is input to one end of the cores a and 20a, the two windings 18a and 20a form the core 1
The two windings 18a and 20a are wound such that the magnetic fields generated in 6a overlap each other. Then, one ends of the two windings 18a and 20a are connected to the input terminals 12a and 1a.
2b, respectively.

Output terminals 22a and 22b are connected to the output terminal of the first choke coil 14a, that is, the other ends of the two windings 18a and 20a, respectively.

Further, the input terminals of the second choke coil 14b are connected to the input terminals 12a and 12b. The second choke coil 14b is for blocking a normal mode signal and passing a common mode noise. The second choke coil 14b includes, for example, a ring-shaped core 16b, and two windings 18b and 20b are wound around the core 16b. In this case, when a normal mode signal is input to one ends of the two windings 18b and 20b, the magnetic fields generated in the core 16b by the two windings 18b and 20b are superimposed on each other, and the one ends of the two windings 18b and 20b are When common mode noise is input to the two windings 18b and 20b, the magnetic fields generated in the core 16b cancel each other.
Two windings 18b and 20b are wound. And 2
One ends of the two windings 18b and 20b are connected to the input terminal 12a.
And 12b, respectively.

The output end of the second choke coil 14b, that is, the other end of the two windings 18b and 20b, is
Each is grounded and terminated via terminating resistors 24a and 24b. These termination resistors 24a and 24b
Are for converting common mode noise into heat and consuming it.

In this common mode choke coil 10, as shown in FIG. 3, when common mode noise of the same phase is input to the input terminals 12a and 12b, the windings 18a and 2 of the first choke coil 14a are input.
The magnetic fields generated in the core 16a are superposed on each other by 0a, and the first choke coil 14a has a high impedance. Further, the winding 18 of the second choke coil 14b
The magnetic fields generated in the core 16b by b and 20b cancel each other out, common mode noise passes through the second choke coil 14b, and the terminating resistors 24a and 24b.
Is converted into heat and consumed. That is, in this common mode choke coil 10, the input terminals 12a and 12
When common mode noise is input to b, the common mode noise is blocked by the first choke coil 14a, passes through the second choke coil 14b, and is converted into heat by the terminating resistors 24a and 24b. Converted and consumed. The relationship between the time and the input voltage of the noise input to the input terminal and the reflected voltage of the noise reflected at the input terminal in this case is shown in FIG. 4, and the time and the applied voltage of the noise applied to the termination resistor and the output terminal The relationship between the output noise and the output voltage is shown in FIG.

Also, this common mode choke coil 1
0, as shown in FIG. 6, the input terminals 12a and 12
When a normal mode signal is input to b, the magnetic fields generated in the core 16a are canceled by the windings 18a and 20a of the first choke coil 14a, and the normal mode signal passes through the first choke coil 14a.
Furthermore, the magnetic fields generated in the core 16b are superposed on each other by the windings 18b and 20b of the second choke coil 14b, and the second choke coil 14b has a high impedance. That is, this common mode choke coil 1
At 0, when a normal mode signal is input to the input terminals 12a and 12b, the normal mode signal is
It is cut off by the second choke coil 14b, passes through the first choke coil 14a, and passes through the output terminal 22a.
And 22b.

Therefore, in this common mode choke coil 10, the normal mode signal is passed and the common mode noise is absorbed. Therefore, in this common mode choke coil 10, it is not necessary to bring it close to the noise generation source or to cover a part of the transmission line with ferrite having large loss in order to suppress radiation of common mode noise. There are no problems such as inconvenient arrangement of parts or lengthy equipment.

Incidentally, this common mode choke coil 1
0 can also be regarded as a device that separates a normal mode signal and a common mode signal when the terminating resistors 24a and 24b are regarded as loads. Further, since the common mode choke coil 10 operates in the same manner for signals whose input and output are in opposite directions, it can be used for purposes other than absorbing noise. FIG. 7 is an illustrative view showing another example of use of the embodiment shown in FIG. In the usage example shown in FIG. 7, the circuit for outputting the audio signal of the radio outputs the output terminal 22 of the common mode choke coil 10 via the buffer amplifier 26.
a and 22b, the other ends of the windings 18b and 20b of the second choke coil 14b of the common mode choke coil 10 are connected to the tuner of the radio via the capacitor 28, and the input terminal 12a of the common mode choke coil 10 is connected. And 12b are connected to the earphone 30. In the use example shown in FIG. 7, the cables 32a and 32b of the earphone 30 also serve as the antenna of the radio tuner.

FIG. 8 is a circuit diagram showing an example of a balanced signal transmission line using the embodiment shown in FIG. In the transmission line shown in FIG. 8, the common mode choke coil 10 is used in each of the rear stage of the driver and the front stage of the receiver.
In the transmission line shown in FIG. 8, a normal mode signal is passed, but common mode noise is generated in each of the common mode choke coils 10 at the rear stage of the driver and the front stage of the receiver.
Is absorbed by.

Although the ring-shaped cores 16a and 16b are used for the first choke coil 14a and the second choke coil 14b in the above embodiment,
The shape of the core used in the choke coil and the second choke coil may be a shape other than the ring shape.

Further, in the first choke coil 14a used in the above-mentioned embodiment, if the input and output ends of one coil 18a or 20a are reversed, the first choke coil 14a is switched to the normal mode signal. Can be used as a second choke coil for blocking the noise and passing common mode noise. Similarly, in the second choke coil 14b, if the input and output ends of one coil 18b or 20b are reversed, the second choke coil 14b passes the normal mode signal and blocks the common mode noise. It can be used as a first choke coil for

Furthermore, in the above-mentioned embodiment, the output end of the second choke coil 14b is terminated via the terminating resistors 24a and 24b, but the output end of the second choke coil is replaced by a common resistor. It may be terminated via another electronic component having an impedance to consume the modal noise.

[Brief description of drawings]

FIG. 1 is an illustrative view showing one embodiment of the present invention;

FIG. 2 is a circuit diagram of the embodiment shown in FIG.

FIG. 3 is an illustrative view showing a state in which common mode noise is input to the embodiment shown in FIG.

FIG. 4 is a graph showing the relationship between time and input voltage and reflected voltage when common mode noise is input to the embodiment shown in FIG.

5 is a graph showing the relationship between time and applied voltage and output voltage when common mode noise is input to the embodiment shown in FIG. 1. FIG.

FIG. 6 is an illustrative view showing a state where a normal mode signal is input to the embodiment shown in FIG.

FIG. 7 is an illustrative view showing another usage example of the embodiment shown in FIG.

8 is a circuit diagram showing an example of a balanced signal transmission line using the embodiment shown in FIG. 1. FIG.

FIG. 9 is an illustrative view showing a state in which a normal mode signal is input to a conventional common mode choke coil.

FIG. 10 is an illustrative view showing a state where common mode noise is input to a conventional common mode choke coil.

FIG. 11 is an illustrative view showing a state where common mode noise is input to a conventional common mode choke coil.

FIG. 12 is a circuit diagram showing an example of a balanced signal transmission line using a conventional common mode choke coil.

[Explanation of symbols]

 10 common mode choke coil 12a, 12b input terminal 14a first choke coil 14b second choke coil 16a, 16b core 18a, 18b, 20a, 20b coil 22a, 22b output terminal 24a, 24b terminating resistor

Claims (2)

[Claims] 1. An input terminal, a first choke coil having an input terminal connected to the input terminal, for passing a normal mode signal and blocking common mode noise, and an output of the first choke coil. An output terminal connected to the terminal, and an input terminal connected to the input terminal, including a second choke coil for blocking a normal mode signal and passing a common mode noise; A common mode choke coil in which the output end of the coil is terminated via an impedance for consuming common mode noise. 2. The common mode choke coil according to claim 1, wherein an output end of the second choke coil is terminated via a terminating resistor.