JPH02206360A - Filter circuit - Google Patents

Abstract

PURPOSE:To miniaturize a power circuit by using a pair of coils constituted from magnetically coupled two coil parts. CONSTITUTION:The title apparatus is provided with a first coil 71, in which magnetically coupled first and second coil parts 71A, 71B are connected in series, and with a second coil 72, in which magnetically coupled third and fourth coil parts 72A, 72B are connected in series. Then, the first and second coils 71 and 72 are inserted in lines L1 and L2 respectively, and a junction between the first and second coil parts 71A and 71B and that between the third and fourth coil parts 72A and 72B are connected by a capacitor 81.

Description

[Detailed description of the invention] The present invention will be explained in the following order.

A: Industrial field of application B: Overview of the invention C: Prior art (Fig. 7) D: Problem to be solved by the invention (Fig. 7) E: Means for solving the problem (Figs. 1 and 6) ) F action (Fig. 1 and Fig. 6) G embodiment (Fig. 1 to Fig. 6) (G1) First embodiment (Fig. 1 to Fig. 4) (G2) Second
Embodiments (FIGS. 5 and 6) (G3) Other embodiments H Effects of the invention A Industrial application field The present invention is applied to, for example, power supply circuits using switching regulator circuits, television receivers, etc. It is suitable for this purpose.

B. Summary of the Invention The present invention provides a filter circuit in which two magnetically coupled
By configuring the filter circuit using a pair of coils composed of two coil parts, a compact filter circuit can be obtained.

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

That is, in FIG. 7, 1 indicates a power supply circuit as a whole, and a commercial power supply is supplied to a switching regulator circuit 4 via first and second filter circuits 2 and 3.

In the switching regulator circuit 4, a diode block 6 performs full-wave rectification of the commercial power supply, and then a smoothing capacitor 7 smoothes the rectified power.

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

Therefore, in the switching transformer 8, a secondary voltage is induced in the secondary winding, and after being rectified by the diode 12, it is outputted via the smoothing capacitor 13 and the ripple filter 14.

On the other hand, the power supply control circuit 15 controls the ripple filter 1
It is composed of a pulse width modulation circuit configured to control the pulse width of the output signal according to the terminal voltage of the power supply control circuit 15, and by controlling the field effect transistor 9 on and off based on the output signal of the power supply control circuit 15, The output voltage of the switching regulator circuit 4 is maintained at a predetermined voltage.

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

Therefore, among the noises output to the power supply lines L1 and L2, after the in-phase noise (i.e. common mode noise) is suppressed in the second filter circuit 3, the first filter circuit 2 suppresses the in-phase noise (i.e. common mode noise). By suppressing the normal mode noise (consisting of normal mode noise), the noise output to the power supply lines L1 and L2 as a whole is suppressed, and unnecessary radiation is reduced.

That is, in the second filter circuit 3, a pair of coils 20 and 21 connected by a magnetic circuit are
The coil 2 is inserted into the power supply lines Ll and L2, respectively.
The switching regulator circuit 4 side terminals of 0 and 21 are grounded through 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 inserted into 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, by selecting the inductance and DC resistance of the coils 20, 21, 25, 26 and the capacitance of the capacitors 22, 23, 28, a sufficient suppression ratio can be obtained for the repetition frequency of the on/off operation of the switching regulator circuit 40, and the If you effectively avoid voltage drops,
A desired output voltage can be obtained by sufficiently suppressing unnecessary radiation output from the power supply lines L1 and L2.

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 made smaller, the whole power supply circuit 1 can be made smaller accordingly.

The present invention has been made in consideration of the above points, and aims to propose a filter circuit that can sufficiently suppress unnecessary radiation and downsize the power supply circuit.

E Means for Solving the Problem In order to solve this problem, in the first invention, the first and second coil portions 71A and 7 are magnetically coupled.
1B connected in series, and a second coil 72 in which magnetically coupled third and fourth coil portions 72A and 72B are connected in series, and the first and second coils 71 and 72 are inserted into the lines LL and L2, and a capacitor 81 is connected between the connection point of the first and second coil portions 71A and 71B and the connection point of the third and fourth coil portions 72A and 72B. .

In the second invention, the first and second magnetically coupled
A first coil 73 has coil portions 73A and 73B connected in series, and a second coil 74 has magnetically coupled third and fourth coil portions 74A and 74B connected in series. The second coils 73 and 74 are connected to the line L1
, L2, and the connection point between the first and second coil portions 73A and 73B is grounded with a first capacitor 85, and the connection point between the third and fourth coil portions 74A and 74B is grounded with a second capacitor 85. Ground at 86.

In the third invention, the first and second magnetically coupled
A first coil 37 has coil portions 37A and 37B connected in series, and a second coil 38 has magnetically coupled third and fourth coil portions 38A and 38B connected in series. The third coil portions 37A and 38A are inserted into the lines L1 and L2, and the second and fourth coil portions 3
7B and 38B are connected by a capacitor 40, and from the connection point of the first and second coil parts 37A and 37B, the second
A bypass is formed through the coil portion 37B, the capacitor 40, and the fourth coil portion 38B to the connection point of the third and fourth coil portions 38A and 38B.

In the fourth invention, the first and second magnetically coupled
A first coil 57 has coil portions 57A and 57B connected in series, and a second coil 58 has magnetically coupled third and fourth coil portions 58A and 58B connected in series.
and first and third coil portions 57A and 58A.
is inserted into the lines L1 and L2, the second coil portion 57B is grounded by the first capacitor 59, and the fourth coil portion 58B is grounded by the second capacitor 60, so that the first and second coils are connected to each other. From the connection point of parts 57A and 57B, a first bypass path to ground via the second coil part 57B and the first capacitor 59, and the third and fourth coil parts 5
From the connection point of 8A and 58B, the fourth coil portion 58B
and a second side path grounded via the second capacitor 60.

F action According to the first invention, the first coil 71 has magnetically coupled first and second coil portions 71A and 71B connected in series, and the magnetically coupled third and fourth coil portions. By connecting the second coil 72, which is made by connecting 72A and 72B in series, with a capacitor 81, a low-pass filter circuit can be constructed in which the attenuation rate for normal mode noise increases rapidly and has a maximum value. As a result, it is possible to obtain a filter circuit for normal mode noise that is compact in size and has a large attenuation rate.

According to the second invention, the first coil 73 has first and second magnetically coupled coil portions 73A and 73B connected in series, and the third and fourth coil portions 74A and 73B have magnetically coupled magnetically coupled first and second coil portions 73A and 73B. By grounding the second coil 74 in which 74B is connected in series with the capacitors 85 and 86, a low-pass filter circuit can be constructed in which the attenuation rate for common mode noise increases rapidly and has a maximum value. I can do it,
This makes it possible to obtain a filter circuit for common mode noise that is compact in size and has a high attenuation rate.

Furthermore, according to the third and fourth inventions, the coil portion 37A
Even if 38A, 57A, and 58A are inserted into the lines L1 and L2, it is not possible to obtain a low-pass filter circuit for normal mode noise or common mode noise in which the attenuation rate increases rapidly and has a maximum value. can.

G example An embodiment of the present invention will be described in detail below with reference to the drawings.

(G1) First Embodiment In FIG. 1, in which parts corresponding to those in FIG. Filter circuits 31 and 32 are used to reduce unnecessary radiation.

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

Coils 37 and 38 are comprised of two coil portions 37A, 37
B, 38A, 38B are connected in series, one coil portion 37A, 38A is inserted into the power supply lines L1 and L2, and the remaining coil portions 37B, 38B are connected by a capacitor 40, whereby the coil portion 37B, capacitor 40, coil part 38B, coils 37 and 3
A side path is formed to connect the 8 connection points.

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

In practice, as shown in FIG.
In , if the inductance of the coil 41 is LF and the capacitance of the capacitor 42 is CF, the cutoff frequency flll is expressed by the following equation, and the attenuation rate gradually increases.

On the other hand, in the low-pass filter circuit 46 composed of two coil parts 44A and 44B, the capacitance of the capacitor 45 is C, the inductance of the coil part 44B connected to the capacitor 45 is LP%, and the number of turns is NP,
When the inductance of the remaining coil portion 44A is 8 and the number of turns is N, the cutoff frequency f,2 is expressed, and the attenuation rate increases rapidly.At this time, at the frequency f7 expressed by the following equation, The attenuation rate becomes maximum.

Therefore, if the frequency f14 is selected to match the repetition frequency of the on/off operation of the switching regulator circuit 4, the unnecessary radiation of the power supply circuit 30 can be significantly reduced compared to the conventional one.

In reality, the noise output from this type of switching regulator circuit 4 is a harmonic signal whose fundamental wave is the repetition frequency of the field effect transistor 9, and as the harmonic order becomes higher, the signal level gradually increases. It has the property of decreasing.

Therefore, in order to sufficiently reduce unnecessary radiation, the largest attenuation factor is required for the fundamental wave component, and in this embodiment, the frequency fN at which the attenuation factor is maximum is selected as the frequency of the fundamental wave component. By doing so, unnecessary radiation can be sufficiently reduced.

Furthermore, by selecting the frequency fx as the frequency of the fundamental wave component in this way, the cutoff frequency rot can be selected to be a higher frequency than in the past.

Therefore, the coils 37 and 38 and the capacitor 40 constituting the filter circuit 31 can be made smaller accordingly, and the filter circuit 31 as a whole can be made smaller.

In this way, it is possible to obtain a compact filter circuit 31 that sufficiently suppresses 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 coil portions 57A, 57B, 58
Coils 57 and 58 divided into A and 58B are grounded by capacitors 60 and 61 to suppress common mode noise.

Therefore, like the filter circuit 31, the second filter circuit 32 can be configured to have a small size, and the common mode noise can be sufficiently suppressed, thus making it possible to obtain the power supply circuit 30 having a small size as a whole.

According to the above configuration, the two magnetically coupled coil portions 37A, 37B, 38A, 38B, 57A, 57B,
By connecting 58A and 58B in series, inserting one of them into the power supply lines Ll and L2, and connecting the rest with a capacitor or grounding, it is possible to rapidly increase the attenuation rate and obtain a maximum value. can.

Therefore, the filter circuits 31 and 32 can be made smaller by that amount, and the power supply circuit 30 as a whole can be made smaller.

(G2) Second Embodiment As shown in FIG. 5, in this embodiment, the coil 37
．． Instead of 38, 57, 58, coils 71, 72, 73, 74 wound around a cylindrical core 70 are used.

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

As a result, as shown in FIG.
3.74, two magnetically coupled coil parts 71A, 71B, 72A, 72B, 73A, 73B,
74A and 74B are connected in series.

On the other hand, in the first filter circuit 80, the coils 71 and 72 are inserted into the power supply lines L1 and L2, and the lead lines of the coils 71 and 72 are connected by a capacitor 81.

In fact, even if the lead wires of the coils 71 and 72 are connected by a capacitor 81 instead of the configuration of the filter circuit 31 shown in FIG. 1, the attenuation rate increases rapidly and forms a local maximum value. can do.

Therefore, in this embodiment as well, it is possible to obtain a filter circuit 80 for normal mode noise that has a large attenuation rate and is compact in size, as in the first embodiment.

Similarly, in the second filter circuit 83, the coil 73
and 74 are inserted into the power supply lines L1 and L2, and the coil 7
The lead wires 3 and 74 are grounded by capacitors 85 and 86, respectively.

Thus, similarly to the first filter circuit 80, it is possible to obtain a filter circuit 83 for common mode noise that is compact in size and has a large attenuation rate.

According to the configuration shown in FIG. 5, even if the filter circuit is configured by drawing out a lead wire from the middle of one coil and dividing the coil into two coil parts, the same effect as in the first embodiment can be obtained. 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 L.
1 and L2, the present invention is not limited to this, and if necessary, only one of the filter circuits for normal mode noise or common mode noise may be inserted in the power supply lines L1 and L2. You can do it like this.

Furthermore, in the above embodiment, a case was described in which a filter circuit was inserted into the power supply lines L1 and L2 of a switching regulator circuit, but the present invention is applicable not only to switching regulator circuits but also to reducing unnecessary radiation of various electronic circuits. It can be widely applied to filter circuits.

Furthermore, in the above-described embodiment, a case was described in which unnecessary radiation is reduced by inserting the line into the power lines L1 and L2, but the present invention is not limited to the power line, but can be inserted into various input/output lines to suppress unnecessary radiation. It can be widely applied when

Effects of the Invention As described above, according to the present invention, two magnetically coupled coil parts are connected in series to form a coil, and the filter circuit is configured with the coil, so that the attenuation rate is large and the size is small. It is possible to obtain a shaped filter circuit.

[Brief explanation of the drawing]

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 the basic configuration of a filter circuit to explain its operation, and Fig. 4 is an explanation of its operation. 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, 7.13.2
2.23.28.40.59.60.81.85.86
・・・・・・Capacitor, 14.20.21.25.2
6.37.38.57.58.71.72.73.74
・・・・・・Coil, 37A, 37B, 38A, 38B
, 57A, 57B, 58A, 58B, 71A. 71B, 72A, 72B, 73A, 73B, 74A, 7
4B... Coil part.

Claims (4)

[Claims] (1) It has a first coil in which magnetically coupled first and second coil portions are connected in series, and a second coil in which magnetically coupled third and fourth coil portions are connected in series. The first and second coils are inserted into the line, and a capacitor is used to connect the connection point between the first and second coil portions and the connection point between the third and fourth coil portions. A filter circuit for normal mode noise, characterized in that: (2) It has a first coil in which magnetically coupled first and second coil portions are connected in series, and a second coil in which magnetically coupled third and fourth coil portions are connected in series. The first and second coils are inserted into the line, the connection point of the first and second coil parts is grounded by a first capacitor, and the connection point of the third and fourth coil parts is grounded. A filter circuit for common mode noise, characterized in that the filter circuit is grounded by a second capacitor. (3) It has a first coil in which magnetically coupled first and second coil portions are connected in series, and a second coil in which magnetically coupled third and fourth coil portions are connected in series. The first and third coil portions are inserted into a line, the second and fourth coil portions are connected by a capacitor, and the second coil portion is connected to the second coil portion from the connection point of the first and second coil portions. A filter for normal mode noise, characterized in that a bypass is formed through the coil section, the capacitor, and the fourth coil section to a connection point between the third and fourth coil sections. circuit. (4) It has a first coil in which magnetically coupled first and second coil parts are connected in series, and a second coil in which magnetically coupled third and fourth coil parts are connected in series. and inserting the first and third coil parts into the line, grounding the second coil part with a first capacitor,
The fourth coil portion is grounded by a second capacitor, and the second coil portion is grounded from the connection point of the first and second coil portions.
from a connection point between the third and fourth coil portions and a first side path that is grounded via the coil portion and the first capacitor, via the fourth coil portion and the second capacitor. 1. A filter circuit for common mode noise, characterized in that a second side path is formed to be grounded.