JPH08213260A - Line filter for defogger heater - Google Patents

Abstract

PURPOSE: To reduce noise entering a radio receiver by forming so that the number of turns of a first coil winding of a choke coil is larger than that of a second coil winding and improving the amount of attenuation of noise due to a line filter. CONSTITUTION: A line filter 3 for eliminating noise entering a power supply line is constituted of a choke coil 3a and a capacitor C1 where a first coil winding L1 and a second coil winding L2 are wound around a ring-shaped magnetic body. Then, one terminal and the other terminal of the capacitor C1 are connected to a power supply side (Point A) and the ground side, respectively, where the number of turns of the first coil winding L1 of the choke coil 3a is increased as compared with that of the second coil winding L2, thus drastically attenuating noise entering the power supply line with a line filter and reducing the noise of the radio receiver.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a line filter connected to a defogger heater for dew used in a rear window of a vehicle, and more particularly, to prevent noise entering a power line from being radiated to a radio receiving antenna. The present invention relates to a line filter having a large amount of noise attenuation to prevent.

[0002]

2. Description of the Related Art FIGS. 3A and 3B are diagrams for explaining the configuration of a conventional line filter, FIG. 3A is a circuit configuration diagram, and FIG. 3B is an equivalent circuit diagram. Hereinafter, description will be given with reference to the drawings. The antenna 11 of the vehicle audio device is provided on the rear window glass of the vehicle. However, a defogger heater 12 is also provided close to the antenna 11 in order to remove the dew attached to the rear window glass and remove the fogging of the window. Therefore, noise that has entered the power line of the defogger heater 12 (especially,
(From a generator or the like) is radiated from the defogger heater 12 to the adjacent antenna 11, and in particular, a radio receiver (not shown)
There is noise in the AM frequency band.

In order to attenuate noise that has entered the line on the power source 14 side, the first winding L11 is formed on the ring-shaped magnetic body.
Further, the line filter 13 composed of the choke coil 13a wound with the second winding L12 and the capacitor C11 is inserted to remove noise that has entered the line of the power supply 14. The equivalent circuit of the line filter 13 is as shown in FIG. 3B, and the impedance Z12 is mainly the first winding L1.
1, the impedance Z13 is mainly represented by the second winding L12, and the impedance Z11 is mainly represented by the capacitor C11. Further, R11 is an internal resistance of the power cable (harness), and V11 is a noise source. By using such a line filter 13, the noise of the power supply line is reduced by about −6 between points A and B, that is, both ends of the radio filter 13.
It was attenuated by dB.

[0004]

Conventionally, the choke coil 13a has the first winding L11 and the second winding L11 so that the magnetic flux is not saturated.
The winding number of the winding wire L12 was substantially equal.
Therefore, if the choke coil is used to construct a line filter for removing the noise that has entered the power supply line, the impedances Z12 and Z12 are equal because the number of turns is substantially equal.
There is a problem that the noise at the point B of the defogger heater portion can be attenuated by only about 6 dB from the point A of the line filter inlet, as a result of 13 being substantially equal.

An object of the present invention is to further improve the amount of noise attenuation by the line filter and reduce the noise that enters the radio receiver.

[0006]

In order to achieve the above object, the present invention is characterized in that a first winding of a choke coil is connected between a first terminal of a defogger heater arranged in the vicinity of an antenna and a power supply, A line filter for a defogger heater in which a second winding of the choke coil is connected between a ground and a second terminal of the defogger heater, and a capacitor is connected between the power supply side of the first winding of the choke coil and the ground, It is characterized in that the choke coil is formed so that the number of turns of the first winding is larger than that of the second winding.

[0007]

By making the number of turns of the first winding on the power supply side of the defogger heater larger than that of the second winding on the ground side, the impedance of the first winding can be made larger than that of the second winding. When a line filter is constructed by using choke coils with different winding ratios, the noise attenuation amount due to the line filter is improved corresponding to the impedance ratio of the windings of the choke coil, so that noise that has entered the power supply line is greatly attenuated. be able to.

[0008]

FIG. 1 is a diagram for explaining the configuration of a line filter according to an embodiment of the present invention. (A) is a circuit diagram, (b) is an equivalent circuit diagram, and (c) is a choke coil structure diagram. is there. FIG. 2 is a diagram showing the noise attenuation effect of the line filter according to the embodiment of the present invention. Hereinafter, description will be given with reference to the drawings.

1 is an antenna of the radio receiver (mainly A
It is provided in the rear window glass of the vehicle in the M frequency band). Numeral 2 is a defogger heater (composed of heating wires (such as nichrome wires)) for defrosting, which is provided inside the vehicle rear window glass or along the surface thereof.
Close to. Reference numeral 3 is a line filter for removing noise that has entered the power supply line, and is a choke coil 3a in which the first winding L1 and the second winding L2 are wound on the ring-shaped magnetic body.
And a capacitor C1. One end of the capacitor C1 is connected to the power source side (point A) and the other end is connected to the ground side.
Reference numeral 4 is a power supply (battery) for the defogger heater.

An equivalent circuit of the line filter 3 is shown in FIG.
As shown in (b), the winding portion of the choke coil 3a (first,
The resistance value of the second winding) and the resistance value of the defogger heater 2 are small. If these are ignored, the impedance Z2 is mainly the number of windings of the first winding L1, the impedance Z3 is mainly the number of windings of the second winding L2, and the impedance Z1. Is mainly determined by the capacitance of the capacitor C1. Further, R1 is an internal resistance of the power cable (harness), and V1 is a noise source.

Here, if the number of turns of the first winding L1 of the choke coil 3a is made larger than that of the second winding L2 (see FIG. 1 (c)), the impedance Z2 becomes larger than the impedance Z3 in the winding ratio. It grows substantially in proportion. As a result, the noise attenuation amount when the winding ratio is 1: 1 is -6 dB.
On the other hand, when the winding ratio is 2 to 1, the attenuation is −
9.5 dB, and as an example, the first winding L1 is 3 m
When the winding ratio of H and the second winding L2 is 1 to 1 mH and the winding ratio is 3: 1, the noise is greatly attenuated as the winding ratio is increased to -12 dB.

As shown in FIG. 2, the filter effect is such that, in the frequency band of AM broadcasting, the noise level at the point A (before the filter) is-
6 dB, at a winding ratio of 3: 1 in this embodiment, at point B-
12 dB noise can be attenuated. As described above, in this embodiment, the impedance ratio can be easily changed by using the choke coil in which the ratio of the first winding wire and the second winding wire is changed, and the noise attenuation amount can be greatly improved.

[0013]

As described above, according to the present invention, the noise that has entered the power supply line can be greatly attenuated by the line filter composed of the choke coils having different winding ratios, and the noise of the radio receiver or the like can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a configuration of a line filter according to an embodiment of the present invention, in which (a) is a circuit configuration diagram, (b) is an equivalent circuit,
(C) is a structural diagram of a choke coil.

FIG. 2 is a diagram showing a noise attenuation effect of the line filter according to the embodiment of the present invention.

FIG. 3 is a diagram illustrating a configuration of a conventional line filter,
(A) is a circuit configuration diagram and (b) is an equivalent circuit.

[Explanation of symbols]

 1 ... Antenna 2 ... Defogheater 3 ... Line filter 3a ... Choke coil L1 ... First winding L2 ... Second winding C1 ... Capacitor

Claims (1)

[Claims] 1. A first winding of a choke coil is connected between a first terminal of a defogger heater arranged near an antenna and a power source, and a first winding of the choke coil is connected between a ground and a second terminal of the defogger heater. The second winding is connected,
In a defogger heater line filter in which a capacitor is connected between the power supply side of the first winding of the choke coil and the ground, the number of turns of the first winding of the choke coil is larger than that of the second winding. A line filter for a defogger heater, wherein the line filter is formed as follows.