JP4742305B2 - Noise filter - Google Patents

Description

  The present invention relates to a noise filter that is connected to a power line or a ground line inside a commercial power supply or a power supply device, and suppresses high-frequency pulsation components and noise flowing out from the power supply device or the like.

  The noise filter having the simplest configuration is composed only of a reactor and serves to suppress noise such as high frequency components of commercial frequencies and high frequency pulsation components of the order of kHz or higher. This type of noise filter is described in Patent Document 1, for example, and the noise filter described in this document will be described below.

FIG. 6 shows an example in which the noise filter 2 composed of one reactor 1 shown in FIG. 6A is connected to the power line 20 connecting the power system 7 and the power supply device 5 as shown in FIG.
Noise filter 2 has the effect of suppressing the noise current i _n to be flowing out from the noise source 6 present inside the power supply 5 to the power system 7. Here, _assuming that the inductance of the reactor 1 is L _f , the effect of suppressing the noise current in depends on the impedance Z _{Lf of the} reactor 1 calculated by Expression 1.

For example, when the ratio of the voltage V _Z0 applied to the in-system impedance 8 (whose value is Z ₀ ) and the noise source voltage V _n is obtained, Equation 2 is obtained. As the frequency increases, the impedance Z _Lf increases. it can be seen that the effect of suppressing the current i _n increases.

If the reactor 1 is constituted by an ideal device, the more the impedance Z _Lf frequency increases as shown in Equation 1 becomes large, the effect of suppressing the noise current i _n increases.
However, since an actual reactor has a winding structure, there are innumerable small parasitic capacitances between the windings.
FIG. 7 is a schematic diagram of an actual reactor in which parasitic capacitance is taken into account. FIG. 7A shows a case where a very small parasitic capacitance between the windings is simulated and these are shown as parasitic capacitance 3, and FIG. Is the case where the parasitic capacitance between the windings is combined into one and shown as parasitic capacitance 3. Hereinafter, for simplification, description will be made based on FIG.

In FIG. 7B, the reactor 1 and the parasitic capacitance 3 are connected in parallel. At this time, if the electrostatic capacitance of the parasitic capacitance 3 is C _f , the impedance Z _LC in FIG.

Here, when the voltage V _{Z0 -LC} applied to the in-system impedance 8 is obtained in the same manner as Equation 2, Equation 4 is obtained.

FIG. 8 shows the frequency characteristics of the voltage ratio shown in Equations 2 and 4. However, calculation is performed here assuming that Z ₀ of the impedance 8 in the system is a resistance component.
From FIG. 8, in the calculation result using the ideal reactor obtained from Equation 2, the voltage ratio decreases as the frequency increases. However, as a result of considering the parasitic capacitance expressed by Equation 4, it can be confirmed that the voltage ratio increases with the resonance frequency f = 1 / 2π√ (L _f C _f ) as a boundary. That is, the effect of suppressing the noise current is small in a region other than the resonance frequency.
Further, the actual parasitic capacitance 3 exists innumerably as shown in FIG. 7A, and a plurality of resonance frequencies exist in the high frequency region, so it is difficult to quantitatively grasp the filter characteristics.

  Further, the above description relates to a noise filter having a single-phase configuration with the noise filter 2 consisting of a single reactor 1 and the internal impedance 8 being a resistance component. In addition to the reactor, a combination of a resistor and a capacitor is used. The same problem occurs with various noise filters having a single-phase or multi-phase configuration.

  On the other hand, a filter reactor as shown in Patent Document 2 has been proposed as a filter configuration effective for each of a low-frequency component and a high-frequency component. FIG. 9 shows the circuit configuration.

  In FIG. 9, four windings wound around one core are magnetically coupled to form common mode choke coils 10a to 10d, and capacitors 4a and 4b are connected in parallel to the coils 10c and 10d, respectively. Has been. Here, in the low frequency region, the impedance is increased by parallel resonance between the coils 10c and 10d and the capacitors 4a and 4b to obtain a large attenuation characteristic, and in the high frequency region, the attenuation characteristic is obtained by the impedance of the coils 10a and 10b. It is like that. Thereby, it is possible to configure a filter reactor capable of obtaining attenuation characteristics in both the low frequency region and the high frequency region.

  However, since the attenuation characteristic depends on the impedance characteristics of the coils 10a and 10b in the high-frequency region, in the high-frequency region after the self-resonance frequency determined by the coils 10a and 10b and its parasitic capacitance, the equation 4 shown in FIG. This is similar to the voltage ratio characteristic, and the influence of parasitic capacitance cannot be avoided.

Japanese Patent Laying-Open No. 2005-20448 (paragraphs [0002] to [0004], FIG. 9 and the like) JP-A-8-32394 (paragraphs [0008] to [0010], FIG. 1 etc.)

As described above, in the noise filter using the reactor, the influence of the parasitic capacitance of the reactor becomes dominant in the high frequency region, and the characteristics as an ideal reactor cannot be obtained. It is difficult to grasp the filter characteristics after the lowest resonance frequency determined by the parasitic capacitance, and it is difficult to design a noise filter having a desired attenuation characteristic at a desired frequency.
Accordingly, the problem to be solved by the present invention is to provide a noise filter that can reduce the influence of the parasitic capacitance of the reactor, obtain a characteristic close to an ideal reactor, and obtain a desired attenuation characteristic in a desired high frequency region. There is to do.

In order to solve the above problem, the invention described in claim 1 is a noise filter connected between each pair of input and output terminals.
A first reactor is connected between the first input terminal and the first output terminal, and the first reactor and the second output terminal are substantially equal in inductance value between the second input terminal and the second output terminal. As well as connecting reactors
A first capacitor is connected between the first input terminal and the second output terminal, a second capacitor is connected between the second input terminal and the first output terminal, and the first capacitor And the capacitance of the second capacitor are the same parasitic capacitance common to the first reactor and the second reactor, and the parasitic capacitance formed by combining the parasitic capacitances between the windings into one. It is almost equal .

The invention described in claim 2 is a noise filter connected between each pair of input and output terminals.
A first reactor is connected between the first input terminal and the first output terminal, and the first reactor and the second output terminal are substantially equal in inductance value between the second input terminal and the second output terminal. As well as connecting reactors
A first capacitor is connected between the first input terminal and the second output terminal, a second capacitor is connected between the second input terminal and the first output terminal, and the first reactor is connected. A third capacitor is connected in parallel to the second reactor, a fourth capacitor is connected in parallel to the second reactor, and the capacitances of the first to fourth capacitors are all made equal. It is the same parasitic capacitance common to one reactor and the second reactor, and is sufficiently larger than the parasitic capacitance formed by combining the parasitic capacitances between the windings into one .

The invention described in claim 3, Oite the noise filter according to claim 1 or claim 2,
A first damping resistor is inserted in a series circuit of a first input terminal, a first capacitor, and a second output terminal, and the second input terminal, the second capacitor, and the first output terminal A second damping resistor is inserted in the series circuit .

  According to the present invention, it is possible to realize a noise filter having characteristics close to an ideal reactor by reducing the influence of the parasitic capacitance of the reactor with a very simple circuit configuration. In addition, it is possible to design a noise filter having a desired attenuation characteristic in a desired high frequency region.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a circuit configuration diagram showing a first embodiment of the present invention, and shows a two-terminal pair noise filter.

In FIG. 1, a first reactor 1 a is connected between a first input terminal A and a first output terminal C, and a second reactor is connected between a second input terminal B and a second output terminal D. Two reactors 1b are connected. Incidentally, these reactors 1a, inductance 1b are both similar to FIG. 6, _{L f.} A first capacitor 4a is connected between the first input terminal A and the second output terminal D, and a second capacitor 4b is connected between the second input terminal B and the first output terminal C. Is connected.
Here, the capacitance of the capacitor 4a, 4b is a reactor 1a, a parasitic capacitance 3a 1b, the set substantially equal to 3b value _{C f.}

FIG. 2 is a circuit configuration diagram of a usage example in which the noise filter 10 configured as shown in FIG. 1 is connected between the power system 7 and the power supply device 5. The same reference numerals as those in FIG.
Now, as in the case of the calculation using Expression 2, the ratio of the voltage V _Z0-1 applied to the in-system impedance 8 and the noise source voltage V _n is calculated as Expression 5. Z ₀ is the value of in-system impedance 8 as described above.

FIG. 3 shows the frequency characteristic of the voltage ratio obtained by Equation 5, which corresponds to FIG. Here, similarly to FIG. 8, the calculation is performed assuming that Z ₀ is a resistance component.

According to FIG. 3, the voltage ratio according to Equation 5 has a maximum value at the frequency f _max1 = 1 / 2π√ (2L _f C _f ) and a large peak is generated, but the frequency f _min1 = _1/1 / Even in a frequency region higher than 2π√ (L _f C _f ), it can be confirmed that the attenuation characteristic is better than that of the expression 4 in FIG. This is because the influence of the parasitic capacitances 3a and 3b of the reactors 1a and 1b can be reduced by connecting the noise filter 10 of FIG. 1 between the power system 7 and the power supply device 5, and even in the high frequency region, FIG. It has a characteristic close to an ideal reactor such as the characteristic of Formula 2 in FIG.

  Therefore, according to this embodiment, the influence of the parasitic capacitance of the reactor is reduced, and characteristics close to an ideal reactor can be obtained in a high frequency region. Further, since the inductance of the reactor can be grasped, it is possible to realize a noise filter having a desired attenuation characteristic at a desired frequency in a high frequency region.

Next, FIG. 4 is a circuit configuration diagram showing a second embodiment of the present invention.
In the first embodiment shown in FIG. 1, the capacitors 4a and 4b must be set to have substantially the same capacitance as the parasitic capacitances 3a and 3b of the reactors 1a and 1b. For this reason, not only must the characteristics of the reactors 1a and 1b be grasped in advance, but when the variations of the parasitic capacitances 3a and 3b are large, it is not easy to select the capacitors 4a and 4b. Further, since the frequencies f _max1 and f _min1 taking the maximum value and the minimum value shown in FIG. 3 cannot be set arbitrarily, there is still room for improvement in the design of the noise filter.

Therefore, in the second embodiment of the present invention, in addition to the configuration of FIG. 1, third and fourth capacitors 4c and 4d are connected in parallel with the first and second reactors 1a and 1b, respectively, The capacitances of the fourth capacitors 4a, 4b, 4c, and 4d are made equal, and the capacitances of these capacitors 4a to 4d are made sufficiently larger than the parasitic capacitances 3a and 3b of the reactors 1a and 1b. did. For this reason, even if the parasitic capacitances 3a and 3b vary in size, the capacitances of the capacitors 4c and 4d become dominant, so that no problem occurs.
Here, when the parasitic capacitances 3a and 3b can be accurately grasped, the parallel capacitance of the parasitic capacitance 3a and the capacitor 4c, the parallel capacitance of the parasitic capacitance 3b and the capacitor 4d, and the capacitance of the capacitors 4a and 4b are made equal. May be. In this case as well, the resonance point can be changed.

That is, when the capacitance of the capacitor 4a~4b in FIG 4, _{C f1,} parasitic capacitance 3a and the capacitor 4c, and the parasitic capacitance 3b and the capacitor 4d are connected in parallel both but, capacitors 4c, 4d of Since the electrostatic capacitance is sufficiently larger than the parasitic capacitances 3a and 3b, the parasitic capacitances 3a and 3b can be ignored as capacitors connected in parallel to the reactors 1a and 1b.
When the noise filter of FIG. 4 is connected instead of the noise filter 10 of FIG. 2, the ratio between the voltage V _Z0-2 applied to the in-system impedance 8 and the noise source voltage V _n is obtained in the same manner as Equation 5. Equation 6 is obtained.

From Equation 6, the frequency that takes the maximum value of the attenuation characteristic is f _max2 = 1 / 2π√ (2L _f C _f1 ), and the frequency that takes the minimum value is f _min2 = 1 / 2π√ (L _f C _f1 ), and L _f , C _f1 can be set arbitrarily, and the frequencies f _max2 and f _min2 taking the maximum value and the minimum value can also be set arbitrarily. Thereby, the noise filter which attenuates noise effectively can be designed arbitrarily.
The attenuation characteristic of Equation 6 is substantially the same as that of FIG. 3 except for the frequency having the maximum value and the minimum value, and a characteristic close to an ideal reactor can be obtained in the high frequency region.

Next, FIG. 5 is a circuit configuration diagram showing a third embodiment of the present invention.
FIG. 5A shows an example in which damping resistors 9a and 9b are connected in series to the capacitors 4a and 4b in FIG. 1, respectively. FIG. 5B shows damping resistors 9a and 9b in series with the capacitors 4a and 4b in FIG. This is an example of connection.

In the case of the noise filter shown in FIGS. 1 and 4, there is a frequency at which a voltage peak value is generated, such as f _max1 = 1 / 2π√ (2L _f C _f ) in FIG. At the frequency at which this voltage peak value occurs, not only does it not have the effect of attenuating noise, but it may increase noise.

Therefore, in this embodiment, the damping resistors 9a and 9b are connected in series with the capacitors 4a and 4b, respectively, so as to suppress noise.
That is, the damping resistors 9a and 9b serve to suppress the voltage peak value generated at the resonance frequency in the LC low-pass filter composed of the reactor and the capacitor. For example, the frequency f _max1 = 1 / 2π√ (2L in FIG. The generation of the voltage peak value in _f C _f ) can be suppressed. Here, the resistance values of the damping resistors 9a and 9b may be set in consideration of the noise suppression effect at f _max1 and the loss generated by the damping resistors 9a and 9b.
The attenuation characteristics of this embodiment are substantially the same as those in FIG. 3 except for the frequency at which the maximum value is obtained. As the operational effect, the characteristics close to the ideal reactor in the high frequency region as in the first and second embodiments. Can be obtained.

It is a circuit block diagram which shows 1st Embodiment of this invention. It is a circuit block diagram which shows the usage example of the noise filter shown in FIG. It is a figure which shows the frequency characteristic of the voltage ratio of Numerical formula 5. It is a circuit block diagram which shows 2nd Embodiment of this invention. It is a circuit block diagram which shows 3rd Embodiment of this invention. It is a circuit block diagram which shows a prior art. It is a schematic diagram of the actual reactor which considered the parasitic capacitance. It is a figure which shows the frequency characteristic of the voltage ratio shown to Numerical formula 2 and Numerical formula 4. FIG. It is a circuit block diagram which shows another prior art.

Explanation of symbols

1a, 1b: Reactors 3a, 3b: Parasitic capacitances 4a, 4b, 4c, 4d: Capacitor 5: Power supply 6: Noise source 7: Power system 8: In-system impedance 9a, 9b: Damping resistor 10: Noise filter 20: Power line A, B, C, D: Terminal

Claims (3)

In the noise filter connected between each pair of input and output terminals,
A first reactor is connected between the first input terminal and the first output terminal, and the first reactor and the second output terminal are substantially equal in inductance value between the second input terminal and the second output terminal. As well as connecting reactors
A first capacitor is connected between the first input terminal and the second output terminal, a second capacitor is connected between the second input terminal and the first output terminal, and the first capacitor And the capacitance of the second capacitor are the same parasitic capacitance common to the first reactor and the second reactor, and the parasitic capacitance formed by combining the parasitic capacitances between the windings into one. A noise filter characterized by being almost equal . In the noise filter connected between each pair of input and output terminals,
A first reactor is connected between the first input terminal and the first output terminal, and the first reactor and the second output terminal are substantially equal in inductance value between the second input terminal and the second output terminal. As well as connecting reactors
A first capacitor is connected between the first input terminal and the second output terminal, a second capacitor is connected between the second input terminal and the first output terminal, and the first reactor is connected. A third capacitor in parallel with the second capacitor, a fourth capacitor in parallel with the second reactor,
The capacitances of the first to fourth capacitors are all made equal, and this capacitance is the same parasitic capacitance common to the first reactor and the second reactor, and the parasitic capacitance between the windings is made equal. A noise filter characterized by being sufficiently larger than the parasitic capacitance formed by combining the two . In the noise filter according to claim 1 or 2,
A first damping resistor is inserted in a series circuit of a first input terminal, a first capacitor, and a second output terminal, and the second input terminal, the second capacitor, and the first output terminal A noise filter, wherein a second damping resistor is inserted in the series circuit .

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