JPS60206313A - Line filter - Google Patents

Abstract

PURPOSE:To attain an attenuation characteristic effective even for a high-level noise of high frequency components in the normal use state by using a ferrite core, whose complex permeability is maximum for >=1MHz frequency, as a magnetic core for choke coil. CONSTITUTION:An Ni-Zn ferrite core is given as magnetic materials whose complex permeability mu'' is maximum for >=1MHz frequency, and frequency characteristics of a phase angle theta and an impedance ¦Z¦ of the choke coil using this Ni-Zn ferrite core are shown in figures (a) and (b). A common mode choke coil 7 having an Mn-Zn ferrite core 12 as the magnetic core has a large impedance in a low frequency has a function to eliminate the noise of low frequency components, and a common mode choke coil 8 having an Ni-Zn ferrite core 13 as the magnetic core has a large impedance in a high frequency and eliminates the noise of high frequency components, and thus, the common mode noise is eliminated in a wide band.

Description

[Detailed description of the invention] The present invention relates to a line filter.

In conventional no-line filters, Mn--Zn ferrite having a large initial magnetic permeability μ has been mainly used for the common motor filter magnetic core in order to obtain a large inductance. Graph A in FIG. 1 shows the frequency characteristics of phase angle (θ) and impedance (IZ+) of an example of a choke coil using a general Mn-Zn ferrite core. As is clear from Fig. 1, the choke coil using the conventional Mn-Zn ferrite core is
At moderately low frequencies, it exhibits a large impedance, but at frequencies of several MHz, the impedance decreases and it does not work as a choke coil, resulting in deterioration of the attenuation characteristics for high frequencies. Further, FIG. 2 shows a circuit diagram of a conventional line filter. In order to deal with the deterioration of the above-mentioned choke coil's attenuation characteristics against high frequencies,
Conventionally, the common mode capacitor 2.3 shown in Figure 2 was used.
This was grounded at low impedance so that it could be used for its bypass effect.

However, in many cases, it is extremely difficult to ground the line filters used in the power lines of audio equipment, etc. with low impedance, and in reality they must be grounded with high impedance or used without grounding. ing. Therefore, it was not possible to effectively remove high-frequency common mode noise. Furthermore, as shown in Figure 3C, the actual power supply line has
There is click noise with a high level of high frequency components, and a case where a conventional line filter is used is shown in Figure 3, but the conventional line filter could not remove the high frequency noise.

Additionally, high-frequency noise of approximately 4 Mllz or higher generally causes malfunctions in electronic devices using ICs such as microcomputers, but conventional line filters do not operate normally under normal usage conditions, such as the so-called high impedance noise. An effective filter effect could not be obtained with grounding or no grounding.

The inventor also measured the noise level that affects the output of the audio amplifier. This graph is shown in Figure 3E. It is clear from this graph that high-frequency common mode noise of 5 MHz or higher has a large effect on the amplifier output. This, coupled with the deterioration of the attenuation effect against high-frequency noise, which is the weak point of conventional line filters, There is a need to improve the line filter's attenuation effect on high frequency noise.

In view of the above, an object of the present invention is to provide a line filter that has effective attenuation characteristics even for high-level noise of high-frequency components in normal usage conditions.

In order to achieve the above object, the present invention provides a magnetic core for a B-chip coil with a complex magnetic permeability μ at a frequency of 1 MH2 or more.
It is characterized by the use of a ferrite core with a maximum value of .

In other words, if the line filter is not grounded during normal use, the common mode capacitor loses its effectiveness against common mode noise, and the filter effect is determined by the characteristics of the choke coil.

Therefore, the idea is to use a choke coil that exhibits large impedance at high frequencies. A choke coil having the above-mentioned characteristics can be obtained by using a magnetic material whose complex magnetic permeability μ'' is maximum at a frequency of I MHz or higher for the magnetic core for the choke coil.

Examples of magnetic materials whose complex permeability μ' is maximum at frequencies above I MHz include Ni-Zn1f and ferrite cores, and the phase of a general example of a choke coil using this Ni-Zn ferrite core is The frequency characteristics of the angle (θ) and impedance (IZ+) are shown in FIG. 1B. As shown in this figure, this Ni--Zn ferrite core has a large impedance near 10M11z and acts as an inductor.

By using this Ni--Zn-based ferrite core as a magnetic core for a choke coil, the attenuation effect at high frequencies is enhanced.

In addition, by inserting the choke coil using the Ni-Zn ferrite core according to the present invention in series with the conventional choke coil line, the conventional choke coil can be
Since it operates in a low frequency region around MHz, and the Chiroku coil according to the present invention operates in a high frequency region around 10M2, it is possible to obtain a good attenuation effect over a wide band up to high frequencies.

4 is a circuit diagram of an embodiment according to the present invention. FIG. 4 is a circuit diagram of an embodiment according to the present invention. This implementation series includes a common mode coil 7 whose magnetic core is an Mn-Zn alloy core 12 with an initial permeability μi = 4500, and a common mode capacitor 9.10. It consists of a normal mode capacitor 11 and a common mode coil 8 according to the present invention whose magnetic core is a Ni-Zn ferrite core 15 whose complex magnetic permeability μ' has a maximum value of 200 at 8 MBz. At point 14,
A ground terminal is installed and connected.

In this embodiment, a common mode choke coil 7 having a Mn-Zn ferrite core 12 as a magnetic core according to the prior art has a large impedance at low frequencies and serves to remove noise of low frequency components. A common mode coil 8 having a Ni-Zn ferrite core 15 as its magnetic core has a large impedance at high frequencies, and removes high frequency component noise, and common mode noise over a wide band. Further, when grounded, the common mode capacitor 9.10 serves to remove common mode noise. Of course, the normal mode capacitor 11 removes normal mode noise.

FIG. 5 shows a comparison between the line filter of this embodiment of the present invention and a conventional line filter. FIG. 5 is a graph of the frequency characteristics of the attenuation amount, and graph F is the common mode capacitor 9.10 in FIG. 4 of the embodiment of the present invention.
This is the case where the midpoint 14 of is grounded, and the graph G is the midpoint 1
4 is not grounded, and graph H is the second case of the conventional example.
This is the case where the middle point 6 of the common mode capacitor 2.3 in the figure is grounded, and the graph ■ is the graph when the middle point 6 is not grounded. As is clear from this figure, in the embodiment of the present invention When used with grounding, F shows an extremely large attenuation effect in the entire frequency range, and even when used without grounding in the embodiment of the present invention, at high frequencies of several 10 M1lz or more, the conventional case with grounding shows H It shows an extremely large damping effect.

From this, the line filter of the present invention can have a sufficient filter effect not only when it is grounded, but also when it is used without being grounded.

This eliminates the trouble of providing low-impedance ground wiring when it is generally used as a line filter.As described above, the line filter according to the present invention does not require any particular grounding. ,
It has an effective attenuation effect in a wide band up to high frequencies, and is extremely useful.

[Brief explanation of drawings]

Graph A in FIG. 1 shows the frequency characteristics of the phase angle (θ) and impedance (IZl) of a typical line of choke coils using Mn-Zn ferrite cores used in conventional line filters. Graph B shows the frequency characteristics of the phase angle ll9) and impedance (IZl) of a typical line of choke fill using the Ni-Zn ferrite core according to the present invention. This is a circuit diagram of the filter. Graph C in Figure 3 shows the frequency characteristics of click noise, graph D shows the frequency characteristics when using a conventional filter for click noise, and graph E shows the effect on the output of the audio amplifier. Fig. 4 is a circuit diagram of an embodiment of the present invention, and Fig. 5 shows a case where the embodiment of the present invention is used with grounding, and a case where it is used without grounding. In the case of G1, the frequency characteristics of the attenuation amount are H when the conventional line filter is used with grounding, and I when it is used without grounding. 1.7... Conventional common motor chain coil, 2.
3,9.10...Common mode capacitor, 4.1
1... Normal mode capacitor, 5.12...
Mn-Zn ferrite magnetic core, 6.14...Midpoint of common mode capacitor, 8...Common mode choke coil according to the present invention, 13...N 1 according to the present invention
-Zn-based ferrite magnetic core.

Claims (1)

[Claims] In an AC line filter in which a choke coil is inserted in each line and a capacitor is inserted between the lines, a ferrite core is used as the magnetic core for the choke coil, and the complex magnetic permeability μ' is maximum at a frequency equal to or higher than I Mllz. A line filter that features: