coil

Abstract

By modifying the coil winding method, impedance drop in frequency bands exceeding 10MHz is prevented, and the boost coil functions as a low-pass filter. [Solution] A boost coil 14c is constructed by winding a wire 22 of a predetermined length around an annular core 20 a predetermined number of times. In the winding start region α near the first terminal 30 and the winding end region β near the second terminal 32, the wire 22 is wound in three layers or two and three layers, respectively, while in the remaining intermediate region γ, the wire is wound in a single, aligned layer. The intermediate region γ accounts for 50% to 70% of the circumference of the inner circumference 20a of the core.

Description

Technical Field

[0001] The present invention relates to a coil, and particularly to a coil capable of reducing conduction noise and radiation noise of a PFC circuit (power factor correction circuit) mounted on various electrical appliances.

Background Art

[0002] The main purpose of the coil used in the PFC circuit is to boost the input power supply. However, since this circuit is arranged close to the input power supply, noise generated from transistors and rectifier diodes conducts through the power line, and there is a risk that the conduction noise and radiation noise may exceed the standard values. Therefore, in a band of 1 MHz or higher, the boost coil also serves as a low-pass filter.

Disclosure of the Invention

Problems to be Solved by the Invention

[0003] The inductance of the boost coil used in the PFC converter ranges from 100 μH to 2 mH. When a toroidal (doughnut-shaped) core is used, the winding wires are wound in two to three layers. However, in the case of general multilayer winding, the winding wires at the start and end of the winding are close to each other, and parasitic capacitance is formed between the winding wires. As a result, impedance reduction occurs in a band exceeding 10 MHz, and the function as a low-pass filter deteriorates. As a result, a situation occurs where the noise levels of conduction noise and radiation noise exceed the limit values, and it is necessary to use a large noise filter or add a core for reducing radiation noise, resulting in a problem of increased cost.

[0004] The present invention was devised to solve such problems. By devising the winding method of the coil, the reduction of impedance is suppressed, and the function of the coil as a low-pass filter is improved, thereby reducing conduction noise and radiation noise and suppressing the price increase due to strengthening or adding countermeasure components in the power supply unit. While Patent Document 1 discloses a coil device capable of shifting its self-resonant frequency to the higher frequency side, the present invention aims to suppress second, third, fourth, and fifth-order resonances that occur at frequencies higher than the self-resonant frequency. [Patent Document 1] Japanese Patent Publication No. 2017-163026 [Means for solving the problem]

[0005] To achieve the above objective, in the coil according to the present invention, when a wire of a predetermined length is wound around an annular core a predetermined number of times, the wire is wound in three layers or two and three layers in the winding start region near the first terminal and the winding end region near the second terminal, respectively, while the wire is wound in a single, aligned layer in the intermediate region between the two regions. The phrase "3 layers of winding, or 2 and 3 layers of winding" above means that the conductor is wound in one of the following patterns in both the starting and ending winding regions. (a) The wire is wound three times throughout the entire area. (b) Within the region, there is a mixture of areas where the conductor is wound twice and areas where it is wound three times.

[0006] It is desirable that the above-mentioned intermediate region be configured to occupy, for example, 50% to 70% of the circumference of the inner circumference of the core. [Effects of the Invention]

[0007] In the case of the coil according to this invention, the stray capacitance in the starting and ending regions of the winding, where the conductor is wound in three layers or two and three layers, is smaller than that of conventional coils with overlapping windings, thus suppressing impedance reduction in the 10MHz to 100MHz band. By improving the winding method of the coils used in the boost converter, it is possible to reduce conducted and radiated noise, simplify the noise filter in the power supply section, eliminate the need for additional countermeasures components, and significantly reduce costs. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic circuit diagram showing the configuration of a boost converter for PFC according to the present invention. [Figure 2] This is a photograph of an actual coil, showing an example of one used in a boost converter for PFCs. [Figure 3] This diagram schematically shows the configuration of a staggered coil. [Figure 4] This diagram schematically shows the configuration of a two-part wound coil. [Figure 5] This diagram schematically shows the configuration of a three-part wound coil. [Figure 6] This graph shows the difference in impedance characteristics depending on the proportion of the intermediate region γ in a three-part wound coil. [Figure 7] This diagram schematically shows the configuration of a four-part wound coil. [Figure 8] This graph shows the differences in impedance characteristics of coils with different winding methods. [Figure 9] This is an equivalent circuit diagram showing the parasitic capacitance of a staggered coil. [Figure 10] This is an equivalent circuit diagram showing the parasitic capacitance of a two-part wound coil. [Figure 11] This is an equivalent circuit diagram showing the parasitic capacitance of a three-part wound coil. [Figure 12] This is an equivalent circuit diagram showing the parasitic capacitance of a four-part wound coil. [Best Mode for Carrying Out the Invention]

[0009] Figure 1 shows a boost converter circuit 10 used for PFC (power factor correction), where 11 is the AC input, 12 is the bridge rectifier diode, 13 is the film capacitor, 14 is the boost coil, 15 is the transistor, 16 is the rectifier diode, 17 is the electrolytic capacitor, 18 is the load, and 19 is the noise filter.

[0010] FIG. 2 is a photograph of an actual boost coil 14, which is formed by winding a metal wire 22 around a doughnut-shaped core 20 a predetermined number of times (e.g., 65 times). The present invention aims to prevent impedance reduction in a frequency band exceeding 10 MHz by devising the winding method of the coil 14 and making the boost coil 14 function as a low-pass filter. As a result, the propagation of noise generated from the transistor 15 and the rectifier diode 16 to the AC input 11 side is suppressed, and the simplification of the noise filter 19 and the elimination of additional countermeasure components can be achieved.

[0011] FIG. 3 shows a coil 14a wound in the most common conventional "overlapping winding" method. The consecutive numbers (1) to (65) in the figure indicate the number of turns of the wire 22. When forming this overlapping-wound coil 14a, first, one part of the wire 22 divided into two is wound counterclockwise around the core 20 from the position A of (1). At the position B of (43) where the core 20 is almost wound once, the end of the remaining wire 22 is taken out as the first terminal 30. Next, the other part of the wire 22 divided into two is wound counterclockwise around the core 20 from the position C of (44). At the position D of (65) where it is almost wound once, the end of the remaining wire 22 is taken out as the second terminal 32. As a result of the above, the wire 22 is wound around the surface of the core 20 in almost two layers.

[0012] FIG. 4 shows a coil 14b wound in the conventional "two-part winding" method. When forming this two-part wound coil 14b, first, one side (the first part) of the wire 22 divided into two is wound counterclockwise around the core 20 from the position A of (1) and temporarily stopped at the position B of (22) where it is almost wound half a turn. Next, the other side (the second part) of the wire 22 divided into two is wound clockwise around the core 20 from the position C of (23). At the position D of (42) where it is almost wound half a turn, the winding direction is reversed, and it is wound half a turn overlappingly from the position E of (43) to the position F of (53). Next, wind the remaining part of the first portion of the conducting wire 22 counterclockwise from the position G of (54) by half a turn, and take out the end of the conducting wire 22 remaining at the position H of (64) as the first terminal 30. Finally, take out the remainder of the second portion of the conducting wire 22 as the second terminal 32 at the position I of (65). In the case of this two-part wound coil 14b, it is distinguished from the above simple multilayer wound coil 14a in that the multilayer winding is performed in two regions divided from the center of the coil.

[0013] FIG. 5 shows a coil 14c formed by "three-part winding" which is first adopted in the present invention. To form this three-part wound coil 14c, first wind a first portion that occupies approximately 2 / 3 of the length of the conducting wire 22 clockwise around the core 20 from the position A of (1), reverse the winding direction at the position B of (30) after winding approximately 3 / 4 of a turn, and wind in an overlapping manner for approximately 1 / 4 of a turn from the position C of (31) to the position D of (38). Next, reverse the winding direction again, wind in an overlapping manner for approximately 1 / 4 of a turn from the position E of (39) to the position F of (43), and take out the remainder of the first portion as the first terminal 30 there. Next, wind the second portion of the conducting wire 22 counterclockwise around the core 20 from the position G of (44), reverse the winding direction at the position H of (52) after winding approximately 1 / 4 of a turn, and wind in an overlapping manner for approximately 1 / 4 of a turn from the position I of (53) to the position J of (60). Then reverse the winding direction again, wind in an overlapping manner for approximately 1 / 4 of a turn from the position K of (61) to the position L of (65), and take out the remainder of the second portion of the conducting wire 22 as the second terminal 32. Note that the procedure of this winding method is merely an example, and the three-part wound coil 14c may be formed by other procedures.

[0014] In the case of this three-part wound coil 14c, the conducting wire 22 is wound in three layers in the winding start region α close to the first terminal 30. Also, the conducting wire 22 is wound in three layers in the winding end region β close to the second terminal 32. In contrast, in the intermediate region γ sandwiched between the winding start region α and the winding end region β, the conductor 22 is not wound in an overlapping manner, but rather in a single, aligned winding.

[0015] Furthermore, the term "three-layer winding" means that at least a portion of both the winding start region α and the winding end region β contains areas where the conductor 22 is wound three times, and does not exclude the possibility of gaps where the conductor is wound only twice. For example, at position F of the winding start region α, the conductor 22 is stacked in three layers: (43), (31), and (30), but at position D, it is stacked in two layers: (38), (22) and (38), (21).

[0016] Furthermore, the "winding start region α" and "winding end region β" are concepts based on the relative distance between the first terminal 30 and the second terminal 32, as described above, and are unrelated to the actual position on the core 20 where the conductor 22 begins to be wound or where it ends.

[0017] Figure 6 is a graph showing the impedance characteristics of the three-part wound coil 14c, depending on the proportion of the intermediate region γ (the proportion of the circumference of the inner core circumference 20a). As shown in the figure, sufficient impedance reduction suppression is achieved when the proportion of the intermediate region γ is set to 50% (solid line graph) and when it is set to 70% (dotted-dotted line graph).

[0018] Figure 7 shows a coil 14d made using a "four-part winding" method, which was considered for use in the present invention. To form this four-part wound coil 14d, first, one end of the conductor is taken out as the first terminal 30 at position A (1), and then wound around the core counterclockwise up to position B (21). Next, at position C (22), reverse the winding direction and wind approximately 1 / 4 of a turn, overlapping up to position D (29). Next, the winding direction is reversed, and the winding is carried out in a counterclockwise direction from position E at (30) to position F at (32). Then, the first winding of the left half of the core is started from position G at (33) and continued to position H at (44). Next, reverse the winding direction at position I (45), wind the wire clockwise in overlapping directions up to position J (53), then reverse the winding direction again and wind the wire counterclockwise in overlapping directions from position K (54) to position L (56). Next, the first winding of the core is started from position M (57) for the remaining 1 / 4, and the remaining wire is taken out at position N (65) as the second terminal 32.

[0019] In the case of this four-part wound coil 14d, the winding start region near the first terminal 30 and the winding end region near the second terminal 32 are made up of a single layer of aligned winding. Furthermore, the remaining area is divided into two regions, each consisting of three layers of overlapping winding.

[0020] Figure 8 is a graph showing the impedance characteristics of each coil 14a to 14d due to differences in winding method. As shown in the diagram, in the case of the 14a staggered coil, an impedance drop is observed in the bandwidth exceeding 15MHz. Furthermore, in the case of the two-part wound coil 14b, an impedance drop occurs in the bandwidth above 50MHz. In contrast, in the case of the three-part wound coil 14c, where the proportion of the intermediate region γ is set to 50%, the impedance drop is suppressed up to the 90MHz band. In the case of the four-part wound coil 14d, performance is good above 20MHz, but impedance drop occurs in the 13MHz band.

[0021] Below, we will examine the differences in impedance characteristics for each coil based on the equivalent circuit diagrams showing the parasitic capacitance of each coil 14a to 14d. First, in the case of the lap-wound coil 14a shown in Figure 9, a parasitic capacitance C is evenly distributed at the beginning and end of the winding, resulting in impedance drops in the 20MHz, 45MHz, and 95MHz bands.

[0022] Furthermore, in the case of the two-part wound coil 14b shown in Figure 10, a capacitance C is parasitic at the folded point of the conductor 22, resulting in impedance drops in the 45MHz, 85MHz, 95MHz, and 200MHz bands.

[0023] In contrast, in the case of the three-part wound coil 14c shown in Figure 11, capacitance C is parasitic only in the winding start and end regions, and is reduced in the intermediate region. As a result, the impedance drop is limited to the 150MHz band. Since noise generated by transistors and rectifier diodes is predominantly distributed in the 5MHz to 60MHz band, the impedance characteristics of the three-part wound coil 14c are extremely effective for functioning as a low-pass filter.

[0024] In the case of the four-part wound coil 14d shown in Figure 12, the narrow single-layer aligned winding area and the adjacent three-layer overlapping winding section result in an impedance drop in the 13MHz band. However, good results are obtained in the 20MHz to 300MHz band. [Explanation of symbols]

[0025] 10 Boost converter circuit 11 AC inputs 12 Bridge rectifier diodes 13 Film Capacitors 14 coils 14a Overwound coil 14b Two-part wound coil 14c three-part wound coil 14d four-part wound coil 15 transistors 16 Rectifier diode 17 Electrolytic Capacitors 18 load 19 Noise filter 20 cores 20a Core inner circumference 22 Conductor 30 First terminal 32 Second terminal C capacitance

Claims

1. A boost coil is constructed by winding a wire of a predetermined length around a ring-shaped core a predetermined number of times, In the starting winding region near the first terminal and the ending winding region near the second terminal of the coil, the conductor is wound in three layers, or in two and three layers, respectively. A coil characterized in that the conductors are wound in a single, aligned layer in the intermediate region sandwiched between the two regions.

2. The coil according to claim 1, characterized in that the above-mentioned intermediate region occupies 50% to 70% of the circumference of the inner circumference of the core.

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