JPH04355905A - Choke coil and noise-reducing device for switching power supply - Google Patents

Abstract

PURPOSE:To obtain a noise-reducing device, to be used for a core, a choke coil and a switching power supply at low cost, in which a filter circuit can be made small in size at low cost by increasing the leakage inductance of a common mode choke coil L1. CONSTITUTION:In the choke coil having a core 13 constituting a closed magnetic circuit and first and second coils 11 and 12 which are independently wound on the above-mentioned core 13, a leakage inductance part, consisting of magnetic permeable material to be magnetically connected to the closed circuit of the core 13 on the outside of the closed circuit core 13 in the vicinity of the edge part at least on one edge part of the coils 11 and 12, are characteristically provided. When the saturated magnetic flux density of the leakage inductance part is increased, the device can be made small in size.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise reduction device used in switching power supplies and the like, and more particularly to an improvement in the structure of the noise reduction device which is small in size and highly effective in reducing conduction noise.

0002

2. Description of the Related Art In a switching power supply device, a noise reduction device (noise filter circuit) is used, for example, as disclosed in Japanese Patent Laid-Open No. 2-79766 proposed by the present applicant. FIG. 10 is a circuit diagram of a conventionally known switching power supply device. In the figure, in a filter circuit 10, a commercial AC power source is connected to a level terminal L and a neutral terminal N, and a ground terminal G is grounded. The diode bridge DB rectifies the alternating current output from the filter circuit 10, and smoothes it with the capacitor C1. A direct current smoothed by a capacitor C1 is applied to the primary winding n1 of the transformer T, and is turned on and off by a switching element Q such as an FET. Then, a switching signal is induced in the secondary winding n2 of the transformer T, so it is rectified by the diodes D1 and D2, the high frequency component is removed by the choke coil L2, and the electricity is stored in the capacitor C2 and sent to the load side. A DC current of a predetermined voltage Vout is supplied. The output voltage stabilizing circuit detects the output voltage Vout and sends an on/off control signal to the switching element Q so that the output voltage Vout becomes a predetermined constant voltage. Although the filter circuit 10 is provided before the rectifying and smoothing circuit composed of the diode bridge DB and the capacitor C1, it may be provided after the rectifying and smoothing circuit, or may be provided both before and after the rectifying and smoothing circuit.

FIG. 11 is a detailed circuit diagram of the filter circuit 10 described above. The across-the-line capacitor CX1 connects the level terminal L and the neutral terminal N, and a discharge resistor R1 is connected in parallel with it. Common mode choke coil L1 is across-the-line capacitor CX1
Connected to the rear stage, it reduces common mode noise and normal mode noise. The across-the-line capacitor CX2 is connected after the common mode choke coil L1, and the capacitor CY is connected in parallel with this.
1, CY2 is connected. Capacitor CY1, CY
2 has the connection point of both grounded to reduce common mode noise. The main function of the filter circuit 10 is to suppress noise conducted and leaked from the switching power supply to the AC power supply side.

FIG. 12 is an explanatory diagram of noise in the vicinity of the filter circuit 10. The filter circuit 10 has P1 as an input terminal.
, P2, and has output terminals P3 and P4. An AC power supply 2 is connected to the input terminals P1 and P2, and a switching power supply 4 is connected to the output terminals P3 and P4. The switching power supply 4 is grounded via an impedance Z1.

Here, if the switching power supply 4 is a noise source, there are two types: common mode noise current i1 and normal mode noise currents i2 and i3. As shown by the broken line in the figure, the common mode noise current i1 is caused by impedance Z.
1 and the ground and returns to the switching power supply 4. As the impedance Z1, there is a capacitor between the can case of the switching element Q and the heat sink, etc. The normal mode noise current i2 flows from the AC power supply 2 to the filter circuit 10, as shown by the solid line, and the normal mode noise current i3 flows from the switching power supply 4 to the filter circuit 10, as shown by the dashed line. Both of them flow in a route that goes back and forth between two signal lines connecting the AC power supply 2 and the switching power supply 4.

Next, the noise reduction of the filter circuit 10 is divided for each noise. Common mode noise current i1 is generated by common mode choke coil L1 and capacitors CY1 and C.
It is reduced by the action of Y2. That is, the inductance of the common mode choke coil L1 acts as a large impedance to the common mode noise current i1. Further, since the common connection point of the capacitors CY1 and CY2 is grounded, the common mode noise current i1 is circulated to the switching power supply 4 side, and is prevented from leaking to the AC power supply 2 side. The normal mode noise current i2 is generated by the AC power supply 2 due to the action of the across-the-line capacitor CX2.
The normal mode noise current i3 is returned to the source on the switching power supply 4 side by the action of the across-the-line capacitor CX1, and the normal mode noise current i3 is returned to the source on the switching power supply 4 side, and the normal mode noise current i3 is returned to the source on the switching power supply 4 side by the action of the across-the-line capacitor CX1.
The total amount of malmode noise currents i2 and i3 is reduced.

FIG. 13 shows a common mode choke coil L1.
FIG. Common mode choke coil L1
consists of coils 11 and 12 and a core 13 wound around these coils in common, and the core 13 forms a closed magnetic circuit. The main inductance is generated by the magnetic flux φ1 that interlinks with both coils 11 and 12, and the leakage inductance is caused by the magnetic flux φA, φB, and
This is caused by φC. The main inductance contributes to the attenuation of the common mode noise current i1, and the leakage inductance contributes to the attenuation of the normal mode noise currents i2 and i3.

[0008]

[Problem to be Solved by the Invention] However, since the purpose of the conventional common mode choke coil L1 is to increase the main inductance, the leakage inductance is a secondary value determined by the number of turns required to obtain the main inductance. It was nothing more than Therefore, the leakage inductance value is not sufficient to attenuate the normal mode noise current, and the across-the-line capacitors CX1 and C
This was dealt with by increasing the capacity of X2. As a result, the size of the filter circuit 10 increases, resulting in an increase in cost, which becomes a major problem when noise regulation is required, such as in a switching power supply, and a small, low-cost product is desired.

The present invention has solved these problems, and provides a choke coil and a switching power supply device that can reduce the size and cost of the filter circuit by increasing the leakage inductance of the common mode choke coil L1. The present invention aims to provide a noise reduction device.

0010

[Means for Solving the Problems] A first invention to achieve the above object is a choke having a core forming a closed magnetic circuit, and first and second coils independently wound around the core. The core coil is characterized in that a leakage inductance section made of a magnetically permeable material is provided outside the closed magnetic circuit near at least one end of the coil and magnetically continuous with the closed magnetic circuit of the core. Preferably, the saturation magnetic flux density of the magnetically permeable material of the leakage inductance portion is higher than the saturation magnetic flux density of the magnetic material of the core.

[0011] A second invention that achieves this object is as follows:
The choke coil according to the first invention is connected to an AC power source, and the applied AC current is converted to DC by a rectifying and smoothing circuit, and the converted current is converted to a DC voltage of a predetermined voltage by a switching power supply to load the load. This is a switching power supply device characterized by supplying power to the side. Note that the connection relationship between the choke coil and the rectifying and smoothing circuit may be reversed.

[Function] Each component of the present invention has the following function. 1st
Since the coil and the second coil are wound independently,
The common mode noise current flowing through these coils is reduced by the main inductance of the core. Since the leakage inductance section increases the leakage inductance of the core, it reduces the normal mode noise current flowing through these coils. Increasing the saturation magnetic flux density of the leakage inductance portion contributes to miniaturization.

Therefore, if such a choke coil is used in a noise reduction device, the capacitance of the across-the-line capacitor for reducing the normal mode noise current can be small.
The device becomes smaller and costs lower.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below with reference to the drawings. Figure 1
FIG. 1 is a perspective view of a choke coil according to an embodiment of the present invention. In the figure, a first coil 11 has a conductor wire wound around it in a hollow shape, and terminals P1 and P2 are provided at both ends. The second coil 12 is formed by winding a conducting wire in a hollow shape, and terminals P3 and P4 are provided at both ends. The core 13 has a rectangular prism-shaped coil winding part 131 to which the first coil 11 is attached, and a rectangular prism-shaped coil winding part 132 to which the second coil 12 is attached, and these are connected to the comb teeth from the base. It stands out in a shape. This coil winding part 131,1
32 is a part of the core 13, on which a winding wire is wound using a bobbin or the like. The leakage inductance portion 133 is a base portion of the core, and extends like a collar toward the fixed end side of the coil winding portions 131 and 132. Here, a pair of π-shaped cores 13 are used, and both coil winding portions are butted against each other to form a closed magnetic path. This leakage inductance section 13
3 are installed symmetrically in the left and right and up and down directions with respect to the center line.

FIG. 2 is an inductance model diagram of the device shown in FIG. In the core 13, the base portion that constitutes the closed magnetic path and the leakage inductance portion 133 are integrated.
For convenience of explanation, these will be explained separately. Comparing with Figure 12,
The magnetic flux φC' passing through the leakage inductance portion 133 increases, and the leakage inductance of the choke coil increases.

FIG. 3 is a spatial model diagram of the apparatus shown in FIG. Here, the space through which the magnetic flux passes is divided into the following three regions E, F, and G. Region E: Inside of the closed magnetic circuit formed by the core 13. Region F: outside the closed magnetic circuit formed by the core 13,
The part excluding the leakage inductance part. Region G: outside the closed magnetic circuit formed by the core 13,
The part occupied by the leakage inductance section.

FIG. 4 is a magnetic equivalent circuit diagram in FIG. 3. Let the magnetic resistances of regions E, F, and G be RE, RF, and RG, respectively. Here, the magnetic resistances RE, RF, and RG are equal to the magnetic resistance of air, and in the region G, they are virtual values without the leakage inductance portion 133. The magnetic resistance when the leakage inductance part 133 is attached is RG/, where the effective relative magnetic permeability of the core is μr (>1).
μr, and this magnetic resistance becomes the actual magnetic resistance of the region G. Ro is a portion of the core 13, which is a closed magnetic path, through which leakage magnetic flux passes, and since it has a small value compared to the normal magnetic resistances RE, RF, and RG, it can be omitted. The magnetomotive force Vm is due to the coil and is equal to the product of the number of turns N and the current I.

Next, when the leakage inductance of one coil is expressed as L for the coil without the leakage inductance portion 133 and L' for the coil with the leakage inductance portion 133, the following equation holds true.

##EQU00001## Due to the presence of the leakage inductance portion 133, the magnetic resistance of the region G becomes smaller, and the magnetic flux passing through this region increases. This increases the leakage inductance and increases the damping force against normal mode noise.

FIG. 5 is a diagram illustrating the shape of the leakage inductance portion. The core of the part that makes up the closed magnetic circuit has a cross-sectional area of A0
The area in contact with the leakage inductance portion 133 is
Let the height be a0 and the width b0. The size of the portion of the leakage inductance portion 133 that contacts the core 13 is vertical a1 and horizontal b1.
If A1 is the cross-sectional area of the side surface perpendicular to this contact surface and through which the magnetic flux φC' passes, the following relational expression holds true. a0 < a1 , b0 < b1 (For the same material; conditions for protruding into a brim shape) A0 ≧ A1 (conditions for magnetic flux saturation)

[0019]
Subsequently, modified embodiments of the present invention will be described. Figure 6 is the second
(A) is a diagram showing an example of the embodiment, in which the core forming the closed magnetic circuit and the core forming the leakage inductance section are separated.
has leakage inductance portions at both ends, and (B) has only one side. In the figure, a pair of U-shaped cores 134 are constructed with legs facing each other, and coils 11 and 12 are wound around the legs, respectively. The flat cores 135 and 136 are attached to the bid portion of the U-shaped core 134 in a brim or umbrella shape to increase leakage inductance. In this case, U-shaped core 1
34 and the flat cores 135, 136 to make the gap between them as small as possible so that the closed magnetic path and the leakage inductance portion 133 are magnetically continuous. Not only when the leakage inductance portion 133 is provided on both sides, but also when the leakage inductance portion 133 is provided only on one side, there is an effect of increasing the leakage inductance.

FIG. 7 is a perspective view showing the choke coil of FIG. 6 in an assembled state. U-shaped core 134 and flat core 13
A combination core 13' which is a combination of 5 is used. In this way, since the U-shaped core 134 and the flat core 135, which are general-purpose products, are used, manufacturing is easier and the parts cost is lower than when manufacturing a core with a special shape.

Next, the results of actual experiments conducted by the present inventor will be described. The conventional type used a choke coil in which a coil was wound 90 turns each around a bipod of UU18-shaped core material, and the product used in this example used this conventional type with flat cores attached on both sides. . The results are shown in Table 1.

[Table 1] Note that the leakage inductance portion may be made of a material that has an appropriate relative magnetic permeability and is different from the material of the core that constitutes the closed magnetic circuit.

The leakage inductance of the example product is almost doubled compared to the conventional product, but there is no change in the main inductance. Generally, the magnitudes of magnetoresistances RE, RF, and RG are considered to be proportional to the volumes of regions E, F, and G. Therefore, if a core material with RE:RF:RG=1:5:1 and effective relative magnetic permeability μr=10 is used for the leakage inductance portion 133, the leakage inductance becomes 1.9 times. Also,
If necessary, a material different from that of the U-shaped core 134 is used for the flat core 135 and the effective relative magnetic permeability is set to an appropriate value, thereby making it possible to obtain a desired leakage inductance.

FIG. 8 is a block diagram of the third embodiment, in which a toroidal core is used for the choke coil. It represents. Even with a toroidal core, the coils are wound in separate areas, so a leakage inductance portion is provided at the boundary between the coils. Here, the pedestal-shaped core 15 also serves as a pedestal for holding the toroidal core. If multiple leakage inductance parts are provided, pedestal core 1
It is preferable to attach the head core 16 to the side opposite to 5.

Next, an embodiment will be described in which the choke coil is further miniaturized. As explained in Fig. 5, the cross-sectional area A1 of the leakage inductance part is the core 1 forming the closed magnetic path.
Since it is undesirable to saturate earlier than 3, there are certain restrictions. Since the magnetic flux is weaker at the end of the leakage inductance than at the coil winding section, the cross-sectional area needs to be A0 > A1. As a result, when downsizing the choke coil, it is inevitable to downsize the leakage inductance portion.

FIG. 9 is a block diagram showing a fourth embodiment of the present invention. In FIG. 9, parts having the same functions as those in FIG. 2 are given the same reference numerals and their explanations will be omitted. The core 13 is made of a material having a relative magnetic permeability of about 10,000, such as MnZn ferrite or Fe amorphous. For the leakage inductance portion 133, it is preferable to use a magnetic material having a relative magnetic permeability of several tens to several thousand and a saturation magnetic flux density of approximately 1 Tesla or more, such as Fe-Si-Al alloy, 3% silicon steel plate, Adopt pure iron etc. In the figure, the solid line part of the leakage inductance part 133 is that of this embodiment using a material with a high saturation magnetic flux density, and the broken line part shows the case where the leakage inductance part 133 has a saturation magnetic flux density that is almost the same as that of the core 13. . The former requires less cross-sectional area than the latter, resulting in a smaller choke coil.

Next, a theoretical analysis of this embodiment will be performed. The area of magnetic field analysis is divided as shown in FIG. 3, and the magnetic equivalent circuit diagram is shown in FIG. In this case, the magnetic flux φ that generates leakage inductance is given by the following equation.

##EQU00002## Leakage inductance L generated from one coil 11 (12) in FIG. 2 is given by the following equation.

[Equation 3] Here, the magnetic resistance of the leakage inductance part 133 is RG
while maintaining the cross-sectional area A1 as A1/a (a>1)
Select the core material so that In this case, since the magnetic resistances RE, RF and RG do not change, the magnetic flux φ passing through the bypass magnetic path becomes equal, so the magnetic flux density in FIG.
If the magnetic flux density of this embodiment is B2, the following equation holds true.

##EQU00004## Now, let Bm be the saturation magnetic flux density of the leakage inductance section 133 in FIG. 2, and let Bm' be the saturation magnetic flux density of the leakage inductance section 133 of this embodiment. Then, when comparing the magnetic flux densities at the same NI value, the present embodiment has a magnetic flux density a times higher than that of the format shown in FIG. 2, according to (Equation 4). Therefore, both are the same N
In order to saturate at the I value, the following conditions must be satisfied.

[Equation 5] In other words, if the magnetic resistance of the leakage inductance portion 133 is kept equal to that shown in FIG. 2, and a material with a saturation magnetic flux density a times that of the material shown in FIG. While keeping the current value) equal to that in FIG. 2, the cross-sectional area of the leakage inductance portion 133 is reduced to 1/
It can be made a times smaller. As a result, the choke coil can be made smaller.

Normally, the leakage inductance portion is used with an effective relative magnetic permeability in the range of 5 to 50, so the magnetic permeability of the leakage inductance portion may be lower than the material of the core 13. Since the saturation magnetic flux density is high, the leakage inductance portion 133 can be made thin.

[0028]

[Effects of the Invention] As explained above, according to the present invention, a leakage inductance portion is provided in a core constituting a closed magnetic circuit,
Since the leakage inductance is increased, the normal mode noise reduction effect is increased when used as a choke coil. Using a magnetic material with a high saturation magnetic flux density for the material of the leakage inductance part also contributes to miniaturization.

Further, when used as a noise reduction device for a switching power supply, the effect of reducing normal mode noise of the choke coil is increased, so the capacitance of the across-the-line capacitor can be small, and the cost of parts can be reduced. Furthermore, since the area occupied by the filter circuit on the printed circuit board is small, this contributes to downsizing of the switching power supply itself.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a choke coil showing an embodiment of the present invention.

FIG. 2 is an inductance model diagram of the device in FIG. 1;

FIG. 3 is a spatial model diagram of the device in FIG. 1;

FIG. 4 is a magnetic equivalent circuit diagram in FIG. 3;

FIG. 5 is a diagram illustrating the shape of a leakage inductance portion.

FIG. 6 is an explanatory diagram of a second embodiment of the present invention, in which a core forming a closed magnetic circuit and a core forming a leakage inductance portion are separated.

7 is a structural perspective view showing an assembled state of the choke coil of FIG. 6; FIG.

FIG. 8 is a configuration diagram of a third embodiment of the present invention.

FIG. 9 is a configuration diagram of a fourth embodiment of the present invention.

FIG. 10 is a circuit diagram of a conventionally known switching power supply device.

FIG. 11 is a detailed circuit diagram of the filter circuit 10.

FIG. 12 is an explanatory diagram of noise near the filter circuit 10.

FIG. 13 is an explanatory diagram of the operation of the common mode choke coil L1.

[Explanation of symbols]

11, 12...Coil 13...Core 131, 132...Coil winding part 133...Leakage inductance section

Claims (4)

[Claims] Claim 1: A choke coil having a core forming a closed magnetic path and first and second coils wound independently around the core, wherein the closed magnetic path is located near at least one end of the coil. A choke coil characterized in that a leakage inductance portion made of a magnetically permeable material is provided on the outside of the core and is magnetically continuous with the closed magnetic path of the core. 2. A choke coil having a core forming a closed magnetic path and first and second coils wound independently around the core, in which the closed magnetic path is located near at least one end of the coil. A leakage inductance portion is provided on the outside of the core, which is made of a magnetically permeable material that is magnetically continuous with the closed magnetic path of the core, and has a higher saturation magnetic flux density of the magnetic material than the saturation magnetic flux density of the magnetic material of the core. A choke coil characterized by: 3. The choke coil according to claim 1 or 2 is connected to an AC power supply, the applied AC current is converted to DC by a rectifying and smoothing circuit, and the DC current is converted to a predetermined voltage by a switching power supply. A noise reduction device for a switching power supply device, characterized in that the DC voltage is converted to a DC voltage and supplied to the load side. 4. An alternating current sent from an alternating current power source is converted into direct current by a rectifying and smoothing circuit, and the converted current is supplied to a switching power source via the choke coil according to claim 1 or 2, 1. A noise reduction device for a switching power supply device, characterized in that the DC voltage is converted into a predetermined DC voltage and supplied to the load side.