KR102708151B1 - Transformer and circuit board having the same - Google Patents

Abstract

A transformer according to one embodiment of the present invention comprises: a core portion having an upper core and a lower core; a coil portion including a primary coil and a secondary coil at least partially accommodated within the core portion; and a magnetic sheet disposed between the primary coil and the secondary coil; wherein the coil portion may include a first overlapping region in which the primary coil and the secondary coil overlap in a thickness direction, and a second overlapping region in which the first overlapping region and the magnetic sheet overlap in the thickness direction.

Description

{TRANSFORMER AND CIRCUIT BOARD HAVING THE SAME}

The present invention relates to a transformer having excellent leakage inductance characteristics and a circuit board including the transformer.

In general, electronic devices require driving power to operate, and a power supply device, such as a power supply unit (PSU), is essential to supply this driving power to the electronic device.

In particular, in display devices such as flat-panel TVs, slimming is demanded along with larger display sizes, so there is a challenge of reducing thickness while satisfying the increased power consumption of larger displays.

In a power supply unit (PSU), the transformer takes up a relatively large volume compared to other components, so reducing the thickness of the transformer itself is the biggest challenge in making it slimmer.

Figure 1 is an exploded perspective view showing an example of a typical slim transformer configuration.

Referring to Fig. 1, a typical slim transformer (10) includes a secondary coil (13) and a primary coil (14) between an upper core (11) and a lower core (12). The secondary coil (13) is usually composed of a plurality of conductive metal plates, and the primary coil (14) usually has a form in which a conductive wire is wound. Depending on the configuration, a bobbin (not shown) may be placed between the upper core (11) and the lower core (12).

However, when the thickness of the transformer is reduced below a certain level (e.g., 11 mm), there is a problem in that performance degradation due to leakage inductance and parasitic capacitance characteristics becomes prominent. This is explained with reference to FIGS. 2a and 2b.

Figure 2a shows the relationship between the height change of the slim transformer and the leakage inductance, and Figure 2b shows the relationship between the distance change between the primary and secondary coils and the parasitic capacitance.

First, referring to Fig. 2a, although there is some difference depending on the relative size of the gap formed at the point where the upper core (11) and the lower core (12) contact each other (generally the middle foot), if the height of the transformer, for example, the distance between the upper surface of the upper core (11) and the bottom surface of the lower core (12) is 13 mm or less, the leakage inductance becomes very low. If the leakage inductance is low, the performance deviation due to load variation becomes large, which is not desirable. This is because the LC resonant circuit configured by the transformer in the power supply unit (PSU) operates in a narrow band with a relatively narrow operating frequency, and thus the gain change according to the power usage is large. In order to resolve the low leakage inductance, a method of separately adding an inductor including a core and a coil to secure the leakage inductance may be considered. This is because the LC resonant circuit becomes an LLC resonant circuit, and the gain change according to the operating frequency in the LLC resonant circuit is lower than that of the LC resonant circuit. However, if an additional inductor is installed, there is a problem that a separate space is required for mounting the inductor to secure leakage inductance in the power supply unit (PSU).

In addition, referring to Fig. 2b, as the vertical distance between the primary coil (14) and the secondary coil (13) decreases, the parasitic capacitance increases rapidly. For example, when the distance between the primary coil (14) and the secondary coil (13) becomes 200 um or less, the size of the parasitic capacitance becomes 100 pF or more. In a general slim transformer, when the parasitic capacitance exceeds 100 pF, there is a problem of performance deterioration due to electrical coupling, such as voltage increase at low power, insulation weakening, and EMI (electromagnetic interference) characteristic deterioration.

In order to reduce such parasitic capacitance, it may be considered to change the configuration of the secondary coil (13) from a conductive metal plate to a conductive wire type. However, if it is configured as a conductive wire type, there is a problem in that more space for accommodating the secondary coil is required inside the core (11, 12), which increases the height of the transformer. In addition, if the thickness of the core (11, 12) is reduced to secure space for accommodating the secondary coil while maintaining the height of the transformer, there is a problem in that heat generation increases due to an increase in the magnetic flux density inside the core.

The technical problem to be achieved by the present invention is to provide a slim transformer that can be further miniaturized and a circuit board using the same.

In particular, the present invention provides a slim transformer capable of miniaturization while securing leakage inductance and a circuit board using the same.

The technical problems to be achieved in the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by a person having ordinary skill in the technical field to which the present invention belongs from the description below.

A transformer according to one embodiment comprises: a core portion having an upper core and a lower core; a coil portion including a primary coil and a secondary coil at least partially accommodated within the core portion; and a magnetic sheet disposed between the primary coil and the secondary coil; wherein the coil portion may include a first overlapping region in which the primary coil and the secondary coil overlap in a thickness direction, and a second overlapping region in which the first overlapping region and the magnetic sheet overlap in the thickness direction.

For example, the ratio of the planar area of the second overlapping area to the planar area of the first overlapping area may be 20% to 70%.

For example, the magnetic sheet may include an amorphous metal ribbon or a ferrite.

For example, the magnetic sheet may include two or more sheets arranged spaced apart from each other.

For example, the thickness of the magnetic sheet may be 10 um to 200 um.

For example, the investment rate of the magnetic sheet can be from 100 to 5000.

In addition, a circuit board according to one embodiment includes a transformer; and an inductor, wherein the transformer includes: a core portion having an upper core and a lower core; a coil portion including a primary coil and a secondary coil at least partially accommodated within the core portion; and a magnetic sheet disposed between the primary coil and the secondary coil; wherein the coil portion may include a first overlapping region in which the primary coil and the secondary coil overlap in a thickness direction, and a second overlapping region in which the first overlapping region and the magnetic sheet overlap in the thickness direction.

The transformer according to the embodiment can be miniaturized by using a thin magnetic sheet to secure leakage inductance through core sharing. Accordingly, the circuit board including it is also advantageous in slimming.

In addition, the present invention facilitates control of leakage inductance by adjusting the overlapping area between the magnetic sheet and the coil portion.

The effects that can be obtained from the present invention are not limited to the effects mentioned above, and other effects not mentioned can be clearly understood by those skilled in the art to which the present invention belongs from the description below.

Figure 1 is an exploded perspective view showing an example of a typical slim transformer configuration.
Figure 2a shows the relationship between the height change of the slim transformer and the leakage inductance, and Figure 2b shows the relationship between the distance change between the primary and secondary coils and the parasitic capacitance.
FIG. 3 is an exploded perspective view showing an example of a transformer configuration according to one embodiment.
Figure 4 shows an example of a magnetic field distribution form of a transformer according to one embodiment and a transformer according to a comparative example.
FIG. 5 shows an example of a magnetic sheet shape arranged to overlap a coil portion according to one embodiment.
FIG. 6 is a graph showing the relationship between the magnetic sheet configuration and leakage inductance of a transformer according to one embodiment.

The present invention can have various modifications and various embodiments, and specific embodiments are illustrated and described in the drawings. However, this is not intended to limit the present invention to specific embodiments, but should be understood to include all modifications, equivalents, or substitutes included in the spirit and technical scope of the present invention.

Terms including ordinal numbers such as second, first, etc. may be used to describe various components, but the components are not limited by the terms. The terms are only used to distinguish one component from another. For example, without departing from the scope of the present invention, the second component may be referred to as the first component, and similarly, the first component may also be referred to as the second component. The term and/or includes any combination of a plurality of related described items or any item among a plurality of related described items.

When it is said that a component is "connected" or "connected" to another component, it should be understood that it may be directly connected or connected to that other component, but that there may be other components in between. On the other hand, when it is said that a component is "directly connected" or "directly connected" to another component, it should be understood that there are no other components in between.

In the description of the embodiments, the description that each layer (film), region, pattern or structure is formed "on" or "under" the substrate, each layer (film), region, pad or pattern includes both being formed directly or via another layer. The reference to "on" or "under" each layer is described with reference to the drawings. In addition, the thickness or size of each layer (film), region, pattern or structure in the drawings may be modified for clarity and convenience of description, and therefore does not entirely reflect the actual size.

The terminology used in this application is only used to describe specific embodiments and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this application, it should be understood that the terms "comprises" or "has" and the like are intended to specify the presence of a feature, number, step, operation, component, part or combination thereof described in the specification, but do not exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts or combinations thereof.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms defined in commonly used dictionaries, such as those defined in common dictionaries, should be interpreted as having a meaning consistent with the meaning they have in the context of the relevant art, and shall not be interpreted in an idealized or overly formal sense, unless expressly defined in this application.

Hereinafter, a transformer according to the present embodiment will be described in detail with reference to the attached drawings.

FIG. 3 is an exploded perspective view showing an example of a transformer configuration according to one embodiment.

Referring to FIG. 3, a transformer (100) according to one embodiment may include a core portion (111, 112), a coil portion (120, 130), and a magnetic sheet (140). Hereinafter, each component will be described in detail.

The core portion (111, 112) has the characteristics of a magnetic circuit and can act as a path for magnetic flux. The core portion (111, 112) can include an upper core (111) coupled from the upper side and a lower core (112) coupled from the lower side. The two cores (111, 112) can have shapes that are symmetrical to each other in the vertical direction or can have asymmetrical shapes. However, in the following description, it is assumed that they have shapes that are symmetrical to each other in the vertical direction for the convenience of explanation.

Each of the upper core (111) and the lower core (112) may include a body portion in the form of a flat plate and a plurality of leg portions (OL, CL) protruding from the body portion in the thickness direction (i.e., in the Z-axis direction) and extending along a predetermined direction. The plurality of leg portions may include two outer legs (OL) extending along one axis (here, the X-axis) direction on a plane and spaced apart from each other along the other axis (here, the Y-axis) direction, and one middle leg (CL) arranged between the two outer legs (OL).

When the upper core (111) and the lower core (112) are connected vertically, each of the outer and middle legs of the upper core (111) faces the corresponding outer or middle legs of the lower core (112). At this time, a gap of a predetermined distance (for example, 10 to 100 um, but not necessarily limited thereto) may be formed between at least some of the outer or middle leg pairs that face each other.

Additionally, the core portion (111, 112) may include a magnetic material, for example, iron or ferrite, but is not necessarily limited thereto.

The coil section (120, 130) may include a secondary coil (120) and a primary coil (130).

The secondary coil (120) may include a first plate (121) and a second plate (122) having a flat shape. The first plate (121) and the second plate (122) may include a conductive metal (e.g., copper or aluminum), and each may have a planar shape that is symmetrical to each other, but is not necessarily limited thereto. The first plate (121) and the second plate (122) may be aligned and laminated around the middle leg (CL) of the core portion (111, 112) to form one turn each, and an insulating layer (not shown) may be arranged between at least two plates (111, 112). The insulating layer will be described later.

The ends of each plate (121, 122) can be pulled out in the same direction, and at this time, the pulling direction can be opposite to the direction in which the two ends (T) of the conductive wire constituting the primary coil (130) are pulled out, but is not necessarily limited thereto.

The primary coil (130) can be wound around the middle leg (CL), and can be a multi-winding in which a rigid conductor metal, for example, a copper conductor wire, is wound several times in a spiral or flat spiral shape, but is not necessarily limited thereto. For example, the primary coil (130) can be applied with an enameled wire (USTC wire) wrapped with fiber yarn, a Litz wire, a triple insulated wire (TIW: Triple Insulated Wire), etc.

The magnetic sheet (140) can be placed between the primary coil (130) and the secondary coil (120) in the thickness direction (i.e., the Z-axis direction). At this time, the magnetic sheet (140) is placed so that at least a portion overlaps with the region where the primary coil (130) and the secondary coil (120) overlap each other in the thickness direction.

In Fig. 3, the magnetic sheet (140) is illustrated as being composed of a first sheet (141) and a second sheet (142), but this is exemplary, and it is sufficient if the first coil (130) and the second coil (120) overlap each other in the thickness direction and at least partly overlap each other. For example, according to another embodiment, the magnetic sheet (140) may be composed of more than two sheets or one sheet.

Each of the first sheet (141) and the second sheet (142) may have a shape suitable for being accommodated in the space between the midfoot (OL) and the outer foot (OL) of the core portion (111, 112), for example, a rectangular planar shape having a major axis (i.e., X-axis) and a minor axis (i.e., Y-axis), but is not necessarily limited thereto.

The magnetic sheet (140) may include a magnetic material, such as ferrite. Additionally, the magnetic sheet (140) may be composed of an amorphous nano metal ribbon or a laminate in which two or more layers of metal ribbons are laminated.

The investment ratio of the magnetic sheet (140) is preferably 1000 or more, and the thickness may be 10 um or more, more preferably 50 um to 300 um, but is not necessarily limited thereto.

An insulating layer (not shown) may be placed above and below each coil (120, 130) for insulation between the core portion (111, 112) and the magnetic sheet (140). The insulating layer may include at least one material from among ketone, polyimide series, PET (Polyethylene Terephthalate), silicone, and epoxy series, but is not necessarily limited thereto.

Figure 4 shows an example of a magnetic field distribution form of a transformer according to one embodiment and a transformer according to a comparative example.

Referring to FIG. 4, the magnetic field intensity (H-field) distribution of a general transformer (10) is shown at the top, and the magnetic field intensity distribution of a transformer (100) according to an embodiment is shown at the bottom.

First, referring to the top of Fig. 4, it can be seen that the magnetic field intensity is concentrated around the gap (G) between the midribs.

In contrast, referring to the bottom of Fig. 4, it can be seen that the magnetic field distribution is spread to the coil section (410). This is because the magnetic sheet (140) is placed between the primary coil (130) and the secondary coil (120) constituting the transformer (100), thereby reducing the coupling between the primary coil (130) and the secondary coil (120), thereby forcibly causing leakage inductance, thereby securing leakage inductance.

For the upper part of Fig. 4, the coil coupling coefficient between the primary coil (130) and the secondary coil (120) was measured as 0.996, and for the lower part of Fig. 4, the coil coupling coefficient was measured as 0.963.

In this way, the arrangement of the thin-film magnetic sheet (140) can reduce the resonant inductor for the resonant design of the circuit, thereby reducing the manufacturing cost of a circuit board such as a power supply unit (PSU) and miniaturizing the circuit board itself. In addition, the addition of the magnetic sheet (140) has the advantage of not entailing any difficulties in the process.

Hereinafter, with reference to FIG. 5 and Table 1, the change in the characteristics of the transformer according to the ratio of the area where the magnetic sheet (140) overlaps on a plane in the thickness direction among the areas where the primary coil (130) and the secondary coil (120) overlap on a plane in the thickness direction will be described.

FIG. 5 shows an example of a magnetic sheet shape arranged to overlap a coil portion according to one embodiment.

In Fig. 5, for the sake of simple understanding, other components of the transformer (100) are omitted, and only the shape in which the first sheet (141) and the second sheet (142) are arranged on the secondary coil (120) is illustrated. When applying the condition change according to Table 1, the experiment was conducted with all the components illustrated in Fig. 3 combined.

The experimental conditions are as follows.

The magnetic sheets (141, 142) are ferrite sheets, with an investment rate of 3000 and a thickness of 150 μm. The changes in width (W) and length (L) and the arrangement state are shown in Table 1.

The primary coil (130) is a 0.4Ψ * 4 parallel structure made of triple insulated wire (TIW).

The secondary coil (120) is composed of 5 ounce copper plates each forming the first plate (121) and the second plate (122), and the central end of each plate is short-circuited with a center tap structure.

Sample L _S [uH] Q L _L [uH] C[pF] Overlapping area ratio Magnetic sheet specifications and layout Ref 318.8 83.8 2.86 74.6 - Ref N.1 318.3 82.7 15.3 76.5 0.44 Long axis ferrite insert (11.5 * 55 * 0.15 mm * 2ea) N.2 318.2 82.4 9.7 76.7 0.28 Long axis ferrite insert (11.5 * 35 * 0.15 mm * 2ea) N.3 319 83.4 6.75 75.4 0.19 Short direction ferrite insert (11.5 * 35 * 0.15 mm * 2ea) N.4 318.4 95.6 4.5 74.9 0.13 Short direction ferrite insert (11.5 * 35 * 0.15 mm * 2ea) (Tilt) N.5 318.2 82.7 17.65 74.7 0.52 Long axis ferrite insert (11.5 * 90 * 0.15 mm * 2ea) N.6 318.6 82.4 19.7 76.3 0.73 Insert 4 points for long axis and short axis

In Table 1, the comparative example (Ref) sample represents a case where the magnetic sheet (140) is not arranged. In addition, in the column for specifications and arrangement of magnetic sheets in Table 1, the parentheses indicate the specifications of each sheet (141, 142) in the order of 'length (L) * width (W) * thickness'. In addition, the major axis direction ferrite insertion means that the major axis direction of each sheet (141, 142) is arranged spaced apart from each other and parallel to the X-axis, as illustrated in FIG. 5, and the minor axis direction ferrite insertion may mean that the major axis direction of each sheet (141, 142) is arranged parallel to the Y-axis, such as in the form of an area where an end of a secondary coil is arranged or an area (510) opposite thereto.

As shown in Table 1, there is no significant difference in other characteristics, such as series mode inductance (L S ), Q factor (Q), and capacitance ( _C ), depending on the change in the overlapping area ratio (i.e., the ratio of the planar area of the first overlapping region where the primary and secondary coils overlap in the thickness direction to the planar area of the second overlapping region where the first overlapping region and the magnetic sheet overlap in the thickness direction). However, it can be seen that the overlapping area ratio tends to be proportional to the leakage inductance (L _L ). Therefore, the transformer (100) according to the embodiment can adjust the leakage inductance value, which is a design target, by adjusting the overlapping area ratio.

Below, the change in performance of the transformer according to the configuration of the magnetic sheet is explained with reference to FIG. 6 and Tables 2 to 4.

FIG. 6 is a graph showing the relationship between the magnetic sheet configuration and leakage inductance of a transformer according to one embodiment.

Changes according to investment rate Investment rate Lp Ls L _L Core Loss Coil Loss - mH uH uH W mW 100 1.6 11.3 10 31.9 14.9 1,000 1.6 11.4 31.6 31.8 14.9 5,000 1.6 11.4 41.1 31.5 14.9 10,000 1.6 11.4 42.8 31.4 14.9 Max/Min 100.60% 101.00% 436.70% 101.50% 100.00%

First, referring to the upper graph of Fig. 6 and Table 2 above, the change in leakage inductance (L _L ) according to the permeability of the magnetic sheet (140) shows a trend of increasing together with the increase in permeability up to a permeability of 5000 and a tendency of approaching saturation when the permeability exceeds 5000. However, except for the leakage inductance, it had little effect on the series/parallel mode inductance (L _S /L _P ), core loss, coil loss, etc. according to the change in permeability of the magnetic sheet (140).

Changes according to the length of the magnetic sheet length Lp Ls L _L Core Loss Coil Loss mm mH uH uH W mW 10 1.6 11.3 11.8 31.6 14.9 50 1.6 11.4 44.2 31.9 14.9 60 1.6 11.4 49.4 31.5 14.9 70 1.6 11.4 50.5 31.4 14.8 100 1.6 11.4 52.3 31.7 14.8 Max/Min 101.10% 101.20% 442.40% 105.40% 100.60%

In addition, referring to the break graph of FIG. 6 together with Table 3 above, the change in leakage inductance (L _L ) according to the length of the magnetic sheet (140) shows a trend of increasing together with the length increasing up to 60 mm, and a tendency of approaching saturation at a longer length. Here, when the length of the magnetic sheet (corresponding to 'L' in FIG. 5) changes, the thickness and width (corresponding to 'W' in FIG. 5) are fixed, and the increase in length means that the ratio of the planar area of the first overlapping region where the primary coil (130) and the secondary coil (120) overlap in the thickness direction to the planar area of the second overlapping region where the first overlapping region and the magnetic sheet overlap in the thickness direction increases.

However, even here, the change in the length of the magnetic sheet (140) excluding the leakage inductance had little effect on the series/parallel mode inductance (L _S /L _P ), core loss, coil loss, etc.

Lm=300uH, fixed center gap 300um, variation according to sheet thickness thickness Lp Ls L _L Core Loss Coil Loss um mH uH uH W mW - 304.7 2.1 2.1 1.3 14.9 10 306.4 2.1 10.6 1.3 14.8 50 312 2.2 30.3 1.3 14.9 100 313.3 2.2 34.1 1.3 14.8 200 315.6 2.2 37.2 1.3 14.8 300 317 2.2 38.5 1.4 14.8 Max/Min 104.00% 104.10% 1813.90% 104.70% 101.00%

Next, the change in leakage inductance (L _L ) according to the change in the thickness of the magnetic sheet (140) is explained by referring to the lower graph of Fig. 6 and Table 4 above. Under the experimental conditions, the magnetizing inductance (Lm: magnetizing inductance) of the core portion (111, 112) is 300 uH, and the size of the gap (center gap) between the middle legs (CL) is fixed to 300 μm.

The change in leakage inductance (L _L ) according to the thickness of the magnetic sheet (140) shows a tendency to increase together with the thickness up to 100 μm and to approach saturation when the thickness exceeds 200 μm. However, except for the leakage inductance, the change in the thickness of the magnetic sheet (140) had little effect on the series/parallel mode inductance (L _S /L _P ), core loss, and coil loss.

In summary, based on the magnetic sheet of the ferrite material, the investment rate is preferably 100 to 5000, and the ratio of the planar area of the first overlapping region where the primary coil (130) and the secondary coil (120) overlap in the thickness direction to the planar area of the second overlapping region where the first overlapping region and the magnetic sheet overlap in the thickness direction is preferably 20% to 70%. This is because when the planar area ratio is less than 20%, the leakage inductance is too low, and when it exceeds 70%, it is not easy to arrange the magnetic sheets (141, 142) in the longitudinal direction as illustrated in FIG. 5.

In addition, the thickness of the magnetic sheet (140) may be 10 um to 200 um. This is because the leakage inductance is too low when it is less than 10 um, and it is not desirable for slimming compared to the increase in leakage inductance when it exceeds 200 um.

Of course, the specifications of the magnetic sheet (140) described above are exemplary and are not necessarily limited thereto. It is obvious to those skilled in the art that various changes are possible depending on the target leakage inductance and the maximum allowable height of the transformer.

In addition, as described above, the transformer (100) according to the embodiment can form a circuit board that constitutes a power supply unit (PSU) or the like together with other magnetic elements (e.g., inductors).

Although the above has been described with reference to embodiments, these are merely examples and do not limit the present invention. Those skilled in the art to which the present invention pertains will recognize that various modifications and applications not exemplified above are possible without departing from the essential characteristics of the present embodiment. For example, each component specifically shown in the embodiments can be modified and implemented. In addition, the differences related to such modifications and applications should be interpreted as being included in the scope of the present invention defined in the appended claims.

100: Transformer 111, 112: Core
130: Primary coil 120: Secondary coil
140: Magnetic sheet

Claims (7)

A core section having an upper core and a lower core;
A coil section including a primary coil and a secondary coil, at least part of which is accommodated within the core section; and
A magnetic sheet is disposed between the primary coil and the secondary coil;
The above coil part,
A first overlapping region in which the first coil and the second coil overlap in the thickness direction, and
A transformer comprising a first overlapping region and a second overlapping region in which the magnetic sheets overlap in the thickness direction. In the first paragraph,
A transformer, wherein the ratio of the planar area of the second overlapping region to the planar area of the first overlapping region is 20% to 70%. In the first paragraph,
The above magnetic sheet,
A transformer comprising an amorphous metal ribbon or ferrite. In the first paragraph,
The above magnetic sheet,
A transformer comprising two or more sheets arranged spaced apart from each other. In the first paragraph,
The thickness of the above magnetic sheet is,
Transformer, 10um to 200um. In the first paragraph,
The investment rate of the above magnetic sheet is,
100 to 5000 people, transformers. Transformers; and
Including an inductor,
The above transformer,
A core section having an upper core and a lower core;
A coil section including a primary coil and a secondary coil, at least part of which is accommodated within the core section; and
A magnetic sheet is disposed between the primary coil and the secondary coil;
The above coil part,
A first overlapping region in which the first coil and the second coil overlap in the thickness direction, and
A circuit board comprising a first overlapping region and a second overlapping region in which the magnetic sheets overlap in the thickness direction.