JP2784783B2 - Filter circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in the following order.

A Industrial application field B Outline of the invention C Conventional technology (FIG. 7) D Problems to be solved by the invention (FIG. 7) E Means for solving the problems (FIGS. 1 and 6) F action (Figs. 1 and 6) G embodiment (Figs. 1 to 6) (G1) First embodiment (Figs. 1 to 4) (G2) Second embodiment ( (FIGS. 5 and 6) (G3) Other Embodiments H Effects of the Invention A Industrial Field of the Invention The present invention is applied to, for example, a power supply circuit using a switching regulator circuit, a television receiver, and the like. It is suitable.

B. Summary of the Invention According to the present invention, a small-sized filter circuit can be obtained by configuring a filter circuit using a pair of coils formed of two magnetically coupled coil portions in the filter circuit. .

C Conventional Art Conventionally, in this type of filter circuit, various filter circuits have been proposed in order to suppress unnecessary radiation from a power supply circuit and the like (Japanese Utility Model Publication No. 63-38608).

That is, in FIG. 7, reference numeral 1 denotes a power supply circuit as a whole, and through the first and second filter circuits 2 and 3,
Commercial power is supplied to the switching regulator circuit 4.

In the switching regulator circuit 4, the commercial power supply is full-wave rectified by the diode block 6, and then smoothed by the smoothing capacitor 7.

On the other hand, the switching transformer 8 receives the smoothed power at one end of the primary winding, and connects the other end of the primary winding to the field-effect transistor 9. A primary current flows in response to the on / off operation of the effect transistor 9.

Accordingly, in the switching transformer 8, a secondary voltage is induced in the secondary winding, and after the secondary voltage is rectified by the diode 12, the smoothing capacitor 13 and the ripple filter 14 are switched.
The output has been made through.

On the other hand, the power supply control circuit 15
And a pulse width modulation circuit configured to control a pulse width of an output signal in accordance with a terminal voltage of the power supply control circuit 15.
Is turned on and off to maintain the output voltage of the switching regulator circuit 4 at a predetermined voltage.

Thus, in the switching regulator circuit 4, the primary current of the switching transformer 8 is switched by controlling the ON / OFF of the field effect transistor 9.
Noise is generated by the switching, and the noise is output to the power supply lines L1 and L2, causing unnecessary radiation.

Therefore, of the noises output to the power supply lines L1 and L2,
After suppressing in-phase noise (that is, composed of common mode noise) in the second filter circuit 3, suppressing the opposite-phase noise (that is, composed of normal mode noise) in the first filter circuit 2 as a whole, The noise output to the power supply lines L1 and L2 is suppressed to reduce unnecessary radiation.

That is, in the second filter circuit 3, a pair of coils 20 and 21 that are coupled by a magnetic circuit are inserted into the power supply lines L1 and L2, respectively, and the coils 20 and 21 are connected.
The terminal on the switching regulator circuit 4 side is grounded by capacitors 22 and 23, thereby forming a low-pass filter circuit against common mode noise.

On the other hand, in the first filter circuit 2, a pair of independent coils 25 and 26 are interposed in the power supply lines L1 and L2, and the coils 25 and 26 are connected by a capacitor 28. A low-pass filter circuit is configured for mode noise.

Thus, the inductance and the DC resistance of the coils 20, 21, 25 and 26 and the capacitance of the capacitors 22, 23 and 28 are selected to obtain a sufficient suppression ratio with respect to the repetition frequency of the on / off operation of the switching regulator circuit 4. At the same time, if the voltage drop of the commercial power supply is effectively avoided, unnecessary radiation output from the power supply lines L1 and L2 can be sufficiently suppressed to obtain a desired output voltage.

D Problems to be Solved by the Invention By the way, in this type of power supply circuit 1, if the filter circuits 2 and 3 can be downsized, the entire power supply circuit 1 can be downsized accordingly.

The present invention has been made in view of the above points, and has as its object to propose a filter circuit capable of sufficiently suppressing unnecessary radiation and reducing the size of a power supply circuit.

Means for Solving E Problem In order to solve such a problem, in the first invention, a first coil 37 in which first and second coil portions 37A and 37B magnetically coupled are connected in series with a first coil 37 And a second coil 38 in which magnetically coupled third and fourth coil portions 38A and 38B are connected in series.
By inserting 37A and 38A into the lines L1 and L2 and connecting the second and fourth coil portions 37B and 38B with the first capacitor 40, the connection point between the first and second coil portions 37A and 37B , A second bypass portion is formed via the second coil portion 37B, the first capacitor 40, and the fourth coil portion 38B to the connection point of the third and fourth coil portions 38A and 38B.

In the second invention, a third coil in which fifth and sixth coil portions 57A and 57B magnetically coupled are connected in series
57 and magnetically coupled seventh and eighth coil portions 58A
And a fourth coil 58 in which the fifth coil 58B is connected in series.
The seventh coil portions 57A and 58A are interposed in the lines L1 and L2, the sixth coil portion 57B is grounded by the second capacitor 59, and the eighth coil portion 58B is connected to the third capacitor 6
By grounding at 0, the fifth and sixth coil portions 57A
And 57B from the connection point of the sixth coil portion 57B and the second capacitor grounded via the second capacitor 59, and from the connection point of the seventh and eighth coil portions 58A and 58B to the eighth A third bypass which is grounded through the coil portion 58B and the third capacitor 60 is formed.

Thus, according to the first and second aspects, the coil portion
The normal mode having a sharp maximum value in the attenuation factor characteristic by inserting the 37A and 38A, 57A and 58A in the lines L1 and L2 and forming the first to third bypasses having capacitors. A low-pass filter circuit for noise or common mode noise can be obtained.

G Example Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

(G1) First Embodiment In FIG. 1 where parts corresponding to those in FIG. 7 are assigned the same reference numerals, reference numeral 30 denotes a power supply circuit as a whole, and first and second filters are used in place of the filter circuits 2 and 3. Filter circuits 31 and 32
Is used to reduce unnecessary radiation.

That is, in the first filter circuit 31, two windings (hereinafter, referred to as coil portions) 37A, 37B, and 38 are magnetically coupled by winding two windings around one core.
The coils 37 and 38 are formed by A and 38B, respectively.

The coils 37 and 38 have two coil portions 37A, 37B, 38
A and 38B are connected in series and one coil part 37
A and 38B are interposed in the power supply lines L1 and L2, and the remaining coil portions 37B and 38B are connected by the capacitor 40, thereby connecting the coil 37 and the connection point of the coils 37 and 38 with the capacitor 40 and the coil portion 38B. Are formed to form a bypass.

Thus, as shown in FIGS. 2 and 3, the conventional filter circuit is configured based on a low-pass filter circuit 43 including a coil 41 and a capacitor 42, whereas the first filter circuit is configured as a first filter. The circuit 31 is configured based on a low-pass filter circuit 46 composed of a filter 44 and a capacitor 45 divided into two coil portions 44A and 44B.

In practice, as shown in FIG.
In the equation, if the inductance of the coil 41 is L _F and the capacitance of the capacitor 42 is C _F , the following equation is obtained. In cut-off frequency f ₀₁ is represented, gradually decay rate increases.

On the other hand, in the low-pass filter circuit 46 composed of the two coil portions 44A and 44B, the capacitance of the capacitor 45 is C _R , the inductance of the coil portion 44B connected to the capacitor 45 is L _F , and the number of turns is N _P , The remaining coil part 44
Assuming that the inductance of A is L _S and the number of turns is N _S Represents the cut-off frequency f ₀₂ , and the attenuation rate sharply increases. Attenuation rate becomes maximum at in represented by the frequency f _M.

Accordance connexion, so that the repetition frequency of the on-off operation of when to quenching the regulation Yoo regulator circuit 4, be selected the frequency f _M, unwanted radiation of the power supply circuit 30 can be reduced to remarkably than conventionally .

Actually, the noise output from the switching regulator circuit 4 of this type is a harmonic signal having a fundamental frequency based on the repetition frequency of the field-down transistor 9, and the higher the harmonic order, the higher the signal. The level also has the characteristic of gradually decreasing.

Therefore, in order to sufficiently reduce unnecessary radiation, the largest attenuation rate is required for the fundamental wave component, and in this embodiment, the frequency f _{M at} which the attenuation rate is maximized is set to the frequency of the fundamental wave component. By selecting, unnecessary radiation can be sufficiently reduced.

Furthermore, in this manner selecting a frequency f _M of the frequency of the fundamental wave component can be selected higher frequency the cut-off frequency f ₀₂ as compared with the prior art.

Therefore, the coil constituting the filter circuit 31 correspondingly
37, 38 and the capacitor 40 are reduced in size,
The whole can be reduced in size.

Thus, it is possible to obtain a filter circuit 31 having a downsized shape that sufficiently suppresses the normal mode noise, thereby making it possible to downsize the entire configuration of the power supply circuit 30.

On the other hand, in the second filter circuit 32, similarly to the filter circuit 31, the coils 57 and 58 divided into the coil portions 57A, 57B, 58A and 58B are grounded by the capacitors 60 and 61 to suppress common mode noise. It has been made to be.

Therefore, also in the second filter circuit 32, it is possible to configure the second filter circuit 32 in a miniaturized shape similarly to the filter circuit 31, to sufficiently suppress the common mode noise, and to obtain the power supply circuit 30 having a small size as a whole. it can.

According to the above configuration, two magnetically coupled coil portions 37A, 37B, 38A, 38B, 57A, 57B, 58A, 58B are connected in series, and one of them is inserted into the power supply lines L1 and L2. At the same time, by connecting or grounding the rest with a capacitor, the attenuation rate can be rapidly increased and a maximum value can be obtained.

Accordingly, the filter circuits 31 and 32 can be reduced in size accordingly,
The entire power supply circuit 30 can be reduced in size.

(G2) Second Embodiment In this embodiment, as shown in FIG.
Instead of 7, 38, 57, 58, coils 71, 72, 73, 74 wound around a cylindrical core 70 are used.

That is, in the coils 71 to 74, the coated copper wire is wound around the core 70 a predetermined number of times, and the lead wire 73 is provided in the middle of the winding.

Thereby, as shown in FIG. 6, the coils 71, 72, 73,
At 74, two magnetically coupled coil portions 71
A, 71B, 72A, 72B, 73A, 73B, 74A, 74B are respectively formed in series connection.

On the other hand, in the first filter circuit 80, the coils 71 and 72 are interposed between the power supply lines L1 and L2, and the leads of the coils 71 and 72 are connected by the capacitor 81.

Actually, even if the connection between the lead wires of the coils 71 and 72 is connected by the capacitor 81 instead of the configuration of the filter circuit 31 of FIG. 1, the attenuation rate increases rapidly and the maximum value of the attenuation rate is formed. can do.

Therefore, also in this embodiment, a filter circuit 80 for normal mode noise having a large attenuation rate and a small shape can be obtained as in the first embodiment.

Similarly, in the second filter circuit 83, the coils 73 and 74 are interposed in the power supply lines L1 and L2, and the lead wires of the coils 73 and 74 are grounded by capacitors 85 and 86, respectively.

Thus, like the first filter circuit 80, the filter circuit for common mode noise having a small shape and a large attenuation rate is used.
83 can be obtained.

According to the configuration of FIG. 5, the same effect as in the first embodiment can be obtained even if the filter circuit is configured such that a lead wire is drawn out of one coil and the coil is divided into two coil portions. Can be obtained.

(G3) Other embodiments In the above embodiment, the filter circuits for normal mode noise and common mode noise are connected to the power supply line.
Although the description has been given of the case where the filter is interposed in L1 and L2, the present invention is not limited to this, and only one of the filter circuits for normal mode noise or common mode noise is inserted in the power supply lines L1 and L2 as necessary. You may do so.

Further, in the above-described embodiment, the case where the filter circuit is interposed in the power supply lines L1 and L2 of the switching regulator circuit has been described, but the present invention is not limited to the switching regulator circuit, and various electronic circuits may be used. The present invention can be widely applied to a filter circuit for reducing unnecessary radiation.

Further, in the above-described embodiment, the case where unnecessary radiation is reduced by interposing the power supply lines L1 and L2 has been described. However, the present invention is not limited to the power supply line, and the unnecessary radiation can be suppressed by inserting the power supply line into various input / output lines. It can be widely applied to the case.

H Effects of the Invention As described above, according to the present invention, two coils that are magnetically coupled are connected in series to form two coils, and one of the two coils is inserted into a line. At the same time, by forming a bypass connecting a capacitor to each of the other coil portions, it is possible to obtain a small-sized filter circuit having an abrupt maximum value in the attenuation factor characteristic.

[Brief description of the drawings]

FIG. 1 is a connection diagram showing a power supply circuit according to an embodiment of the present invention, FIGS. 2 and 3 are connection diagrams showing a basic configuration of a filter circuit for explaining its operation, and FIG. 4 is an explanation of its operation. FIG. 5 is a perspective view showing a coil according to the second embodiment, FIG. 6 is a connection diagram showing a power supply circuit using the coil, and FIG. 7 is a connection diagram showing a conventional power supply circuit. It is. 1, 30 ... power supply circuit, 2, 3, 31, 32, 80, 81 ... filter circuit, 7, 13, 22, 23, 28, 40, 59, 60, 81, 85,
86 …… Capacitors, 14, 20, 21, 25, 26, 37, 38, 57,
58, 71, 72, 73, 74 ... Coil, 37A, 37B, 38A, 38B,
57A, 57B, 58A, 58B, 71A, 71B, 72A, 72B, 73A, 73B,
74A, 74B ... Coil part.

Claims (2)

(57) [Claims] A first coil in which first and second coil portions magnetically coupled are connected in series; a second coil in which third and fourth coil portions magnetically coupled are connected in series; Connecting the first and second coil portions by interposing the first and third coil portions in a line, and connecting the second and fourth coil portions with a first capacitor. From the point of view, the third and fourth coils are passed through the second coil portion, the first capacitor, and the fourth coil portion.
A first bypass path extending to a connection point of the coil portion of the filter circuit for normal mode noise. 2. A third coil in which fifth and sixth coil portions magnetically coupled are connected in series, and a fourth coil in which seventh and eighth coil portions magnetically coupled are connected in series. Having the fifth and seventh coil portions interposed in a line, grounding the sixth coil portion with a second capacitor, and grounding the eighth coil portion with a third capacitor. Thereby, a second bypass which is grounded from the connection point of the fifth and sixth coil portions via the sixth coil portion and the second capacitor, and a connection between the seventh and eighth coil portions. A filter circuit for common mode noise, wherein a connection point forms an eighth coil portion and a third bypass which is grounded via the third capacitor.