JP2000243637A - Thin inductor and thin dc-to-dc convertor using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin inductor of low cost, which has a large inductance and is effectively miniaturized by clarifying the least necessary thickness of magnetic material to a current value and preventing shortage of thickness and excessive thickness of the magnetic material, and a thin DC/DC converter using the thin inductor. SOLUTION: In a thin inductor 1, spiral conductor patterns are formed on a single surface of both surfaces of an insulating substrate 2 and made into coils 4, 5. Aperture parts 3 are formed in the central parts of the coils. The insulating substrate 2 is sandwiched by plate magnetic materials 9, 11, having protruding parts 10 penetrating the aperture parts 3. The minimum thickness of a plate part of the magnetic material 11 is defined by a current value. At coordinates, where the horizontal axis shows the current value and the vertical axis shows the thickness of magnetic material, the thickness of the magnetic material shown by a straight line determined by a point, where the thickness is 0.2 mm when a current value is 0.1 A and a point where the thickness is 0.8 mm when a current value is 2.0A, is made the minimum thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin inductor used in an electronic circuit and a thin DC-DC converter using the same, and more particularly to a thin inductor having a large inductance and effectively preventing shortage or excessive thickness of a magnetic body. The present invention relates to a small and inexpensive thin inductor and a thin DC-DC converter using the same.

[0002]

2. Description of the Related Art In recent years, small and thin portable electronic devices such as mobile phones, PHSs, and personal computers have rapidly become widespread. Along with this, electronic components constituting electronic circuits have been reduced in size, thickness, and performance. In this type of electronic equipment, a battery having a constant voltage is used as a power supply. However, an electronic circuit often requires various voltages, and a DC-voltage using a magnetic component such as an inductor (choke coil, transformer, etc.) is increasing. A DC converter is used as a power supply circuit.
Such portable electronic devices are required to be further reduced in size and cost, and are required to be small, thin, and have a large allowable current and a large inductance.

Conventionally, inductors include a type in which a coil is wound on a magnetic core, and a green sheet type in which a coil is formed on a magnetic ceramic material by a printing technique. As an inductor at the research stage, there is a thin film inductor of a type in which a magnetic material and a coil are formed on a substrate and manufactured by photolithography fine processing technology. A winding type inductor with a sintered ferrite core wound has a large allowable current value because the inductance can be increased according to the number of windings and the current can flow through the winding coil until the magnetic core is magnetically saturated. However, the size is too large, and there is a limit to miniaturization. In addition, since the green sheet type inductor is produced by printing a printed coil in multiple layers, the inductance can be increased, but the coil resistance is high, the allowable current cannot be increased so much, and the cost is high. Further, if coils are multiplexed in order to secure inductance, the size becomes large. In addition, thin-film type inductors can be miniaturized because they are manufactured by microfabrication, but the thickness of the magnetic film must be increased in order to prevent magnetic saturation of the magnetic core. Since the number of processes is required, the number of steps is increased and the cost is extremely high, which is not practical. In addition, the thin film type has a problem in that the characteristics of the inductance are sensitive to variations in the thickness of each film and the like, so that the characteristics vary greatly.

Therefore, as an inexpensive small inductor, a planar coil is used in place of a winding, and the planar coil is surrounded by a magnetic material or a magnetic film (internal coil type), or the magnetic material or the magnetic film is surrounded by a planar coil. A type (external coil type) has been developed. An example of a small inductor of the internal coil type will be described with reference to the drawings. FIG. 7 is a plan view of a planar coil used for a conventional small inductor. For example, an insulating substrate 4 such as a 25 μm-thick polyimide film is used.
1 is a planar coil in which a spiral conductive pattern 42 is formed by photo-etching a copper foil of about 35 μm thickness on both sides, and the spiral conductive patterns 42 on both sides are connected by through holes 43. FIG. 8A is a cross-sectional view of a planar inductor having a structure in which the above-described planar coil is sandwiched between magnetic materials 45 such as ferrite from above and below via an insulating adhesive 44. In order to further increase the inductance, it is preferable to make the magnetic circuit a closed circuit. FIG. 8B shows the case where the upper and lower ends 45a of the magnetic material are in contact with each other.
FIG. 3C shows an example in which an opening is provided in the center of the planar coil, and the inductance is further increased by inserting a projection 45b of a magnetic material.

On the other hand, DC-DC using a small inductor
As a converter, side view of FIG. 9 (including partial cross-sectional view)
As shown in the figure, a thin DC-DC converter 50 (actual flat type 6-6) made with an electric circuit of a chopper type regulator.
No. 6291). In the figure, an electronic component 52 such as an FET or an IC is formed on one surface of a circuit substrate 51 made of an alumina substrate, and an inductor 55 having a flat coil 53 sandwiched between plate-shaped magnetic members 54 is provided on the back surface with an adhesive or the like. It is fixed at. The flat coil 53 is formed by forming a spiral conductive pattern on a double-sided FPC board, and has external dimensions of 17 mm in width, 21 mm in length, and 730 μm in thickness. The plate-like magnetic material 54 is made of Mn—Zn having a thickness of 0.6 mm.
It is a ferrite plate of the system. The thickness of the inductor 55 is 2 m
m. The size of the obtained thin DC-DC converter is 25 mm × 25 mm × 6 mm (thickness). The output current is 0.5 A DC.

[0006]

When an inductor is used in an electronic circuit such as a DC-DC converter, it is desirable that the inductor is as small and thin as possible, has a large inductance, and has a large allowable current of the coil. However, in the conventional small inductor, when the current increases, the inductance decreases due to the magnetic saturation of the magnetic core. If the thickness of the magnetic material is made sufficiently large to prevent this, there is a problem that the inductor becomes large and goes against the demand for miniaturization. This is because the thickness of the magnetic material is not optimized for the current value used. In other words, the minimum thickness of the magnetic body required for the current value for suppressing the decrease in inductance as much as possible and maintaining the inductance at a constant level is not clear.

[0007] The present invention has been proposed in view of the above problems, and an object of the present invention is to clarify the minimum thickness of a magnetic material necessary for a current value, thereby increasing the inductance and increasing the magnetic material. It is an object of the present invention to provide an inexpensive thin inductor that is effectively reduced in size by preventing shortage or excessive thickness, and a thin DC-DC converter using the same.

[0008]

According to the thin inductor of the present invention, a spiral conductor pattern is formed on one or both sides of an insulating substrate to form a coil, and an opening is formed at least in the center of the coil. In a thin inductor that sandwiches an insulating substrate from above and below with a plate-shaped magnetic material having a protrusion inserted into the portion, the thickness of the flat plate portion of the magnetic material is
It is characterized by being at least the minimum thickness determined from the current value and the inductance. More specifically, in coordinates where the horizontal axis represents the current value and the vertical axis represents the magnetic material thickness, the point where the current value is 0.1 A is 0.2 mm in thickness, and the point where the current value is 2.0 A is the thickness. It is desirable that the thickness of the magnetic body indicated by a straight line determined from the point of 0.8 mm be the minimum thickness. More preferably, the magnetic material thickness indicated by a straight line determined by a point having a thickness of 0.3 mm when the current value is 0.1 A and a point having a thickness of 0.9 mm when the current value is 2.0 A is the minimum thickness. It is characterized by. With this configuration, the thickness of the magnetic body can be adjusted to the minimum required thickness for the current value to suppress the decrease in inductance. Depending on the current value, the thickness of the magnetic body becomes insufficient and the inductance decreases significantly. Or
Depending on the current value, the thickness of the magnetic body is prevented from being excessively increased due to excessive thickness, and an inexpensive thin inductor (choke coil, transformer, etc.) that is effectively reduced in size can be provided. By mounting the thin inductor of the present invention, a small, thin, and inexpensive DC-DC converter and various electronic devices can be provided. The thin inductor of the present invention is a magnetic component having a coil pattern and an inductance, and includes, for example, a choke coil and a transformer.

In the thin DC-DC converter of the present invention, a spiral conductor pattern is formed on one or both surfaces of a part of the insulating circuit board of the DC-DC converter to form a coil, and at least a central portion of the coil is formed. An opening is formed, and a thin inductor comprising an insulating circuit board sandwiched from above and below by a plate-shaped magnetic material having a projection inserted into the opening is provided. With this configuration, DC-DC
Since the circuit board of the converter and the insulating board of the thin inductor that is a component of the converter can be shared, the DC-
The DC converter can be significantly reduced in size and thickness.

In the thin DC-DC converter of the present invention, a spiral conductor pattern is formed on one or both sides of an insulating circuit board of the DC-DC converter to form a coil.
An opening is formed at least in the center of the coil, and a thin inductor having an insulating circuit board sandwiched from above and below by a flat magnetic body having a projection inserted into the opening is provided. The thickness of the flat part of the magnetic material is
It is characterized by being at least the minimum thickness determined from the current value and the inductance. With this configuration, it is possible to provide an inexpensive thin inductor that has a large inductance and is effectively reduced in size by preventing the thickness of the magnetic material from being insufficient or excessive, and a thin DC-DC converter using the same.

Further, in the thin DC-DC converter of the present invention, the thickness of the flat portion of the magnetic material of the thin inductor as a component is not less than the minimum thickness determined from the current value and the inductance. Then, on a coordinate where the horizontal axis represents the current value and the vertical axis represents the magnetic material thickness, the current value is 0.1.
The point that the thickness is 0.2 mm at A, and the current value is 2.0 A
In this case, the minimum thickness is a magnetic material thickness indicated by a straight line determined from a point having a thickness of 0.8 mm. More preferably, the magnetic material thickness indicated by a straight line determined by a point having a thickness of 0.3 mm when the current value is 0.1 A and a point having a thickness of 0.9 mm when the current value is 2.0 A is the minimum thickness. It is characterized by. With this configuration, the thickness of the magnetic body can be adjusted to the minimum required thickness for the current value to suppress the decrease in inductance. Depending on the current value, the thickness of the magnetic body becomes insufficient and the inductance decreases significantly. It is possible to provide an inexpensive thin inductor (choke coil, transformer, etc.) that is effectively reduced in size, and that the thickness of the magnetic material is not excessively increased due to excessive current depending on the current value. By mounting this thin inductor, a small, thin, and inexpensive DC-DC converter and various electronic devices can be provided.

Further, the insulating circuit board may be mounted on one side or both sides F
By using a PC board, a thin, high-strength board can be formed, and a circuit pattern of a DC-DC converter including an inductor can be formed at a time. Therefore, a small, thin, and inexpensive DC-DC converter can be provided.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a thin inductor according to the present invention will be described with reference to the drawings. This first embodiment is a thin choke coil. FIG. 1A is a plan view of a thin inductor 1 of the present invention (a magnetic material is not shown), and FIG. 1B is a cross-sectional view of the thin inductor 1 taken along line AB. In FIG. 1, an opening 3 is formed at the center of an insulating substrate 2 made of a resin film such as polyimide. A first coil 4 made of a conductive pattern obtained by spirally patterning a copper foil having a thickness of about 35 μm around an opening 3 on the upper surface of the insulating substrate 2.
Is formed, and a second coil 5 (broken line) is formed of a similar spiral conductive pattern at a symmetrical position on the lower surface of the insulating substrate 2.
Is formed, and the end of the first coil 4 and the start of the second coil 5 are electrically connected to each other through the through holes 6 formed in the insulating substrate 2, and currents in the same direction are applied to the coils 4 and 5. Connected to flow. The end of the coil 5 is connected to the external lead connection land on the upper surface of the substrate 2 via the through hole 8. A flat upper core 9 made of a magnetic material such as ferrite is disposed above the insulating substrate 2 on which the coil is formed, and the same material having a protrusion 10 at the center below the insulating substrate 2 is provided. Lower core 1
1, the protrusion 10 is inserted into the opening 3 of the insulating substrate 2, the end face 10a of the protrusion 10 is brought into close contact with the lower surface of the upper core 9, and the insulating substrate 2 is sandwiched between the cores 9, 11. Thereby, the basic structure of the thin inductor 1 of the present invention is obtained.
In this embodiment, the coils are formed on both sides of the insulating substrate 2, but may be formed on one side only, or the coils on one side or both sides may be laminated in two or more layers. Generally, as the number of coil layers increases, the inductance at the same current increases.

As described above, a large inductance can be obtained when the magnetic body (projection 10) is inserted through the opening of the coil. Further, by bringing the end face 10 a of the projection 10 of the lower core 11 into close contact with the lower face of the upper core 9,
Further, the inductance can be increased.

A feature of the thin inductor of the present invention is that the thickness of the flat plate portion of each core is set in accordance with the inductance and the current value. That is, the minimum thickness of the flat plate portion of the core made of a magnetic material is defined in relation to an inductance of a certain level or more and a current value. More specifically,
If the current value is 0.1 A and the current value is 0.1 A, the thickness is 0.2 mm, and if the current value is 2.0 A, the thickness is 0.8 mm. The thickness of the magnetic body indicated by a straight line connecting the points is set to the minimum thickness. With this configuration, the thickness of the magnetic material can be adjusted to the minimum necessary thickness with respect to the current value to suppress the decrease in inductance, and the inductance can be reduced to 92% or more of the maximum value for each current value. Can be maintained,
Depending on the current value, the thickness of the magnetic body is insufficient and inductance is greatly reduced, and depending on the current value, the magnetic body thickness is prevented from becoming excessive and unnecessarily large, etc., and the balance between characteristics and miniaturization Thus, an inexpensive thin inductor excellent in the above can be provided.

The above-mentioned features were predicted by the present inventors by three-dimensional magnetic field analysis and confirmed by trial production. Hereinafter, description will be made with reference to the drawings. FIG. 2 shows a result obtained by performing a simulation by a three-dimensional magnetic field analysis on the relationship between the thickness of the magnetic core (ferrite core) and the inductance when the coil current is used as a parameter in the thin inductor having the above structure. The inductance was determined by counting the magnetic flux linking the inside of the coil. The coil current at the time of analysis assumes a DC current. In this case, the coil has six turns of one layer on the upper surface of the insulating substrate 2 and six turns of one layer on the lower surface. When the magnetic core was sufficiently thick (about 2 mm or more), the inductance showed a constant value of 15.3 μH regardless of the coil current. In FIG. 2, this is set to 100%. When the magnetic core becomes thinner, the core is gradually magnetically saturated and magnetic flux leaks. As a result, the inductance is gradually reduced. The critical value of the core thickness at which the inductance sharply decreases is 0.1 at 0.1 A.
It can be read as 2 mm, and the inductance at this time is 14.0.
μH, which is approximately 92% of 15.3 μH. Also, at 2.0 A, it can be read as 0.8 mm, which is also 14.0 μH, which is approximately 92% of 15.3 μH. The magnetic core thickness of the thin inductor is desirably in a range where the inductance is large and does not decrease much. Therefore, the "range where the inductance is large and does not decrease much" can be a range of about 92% or more of the maximum value. From the graph of FIG. 2, the magnetic core thickness showing an inductance of about 92% with respect to the maximum value (15.3 μH in this case) is 0.2 mm at 0.1 A and 0.8 mm at 2.0 A. Becomes Therefore, the straight line connecting these points plotted in FIG. 3 corresponds to approximately 92% of the inductance, and the upper side (the region indicated by oblique lines) above this straight line corresponds to “the range where the inductance is large and does not decrease much”. The range of the magnetic core thickness desirable as the thin inductor of the present invention is shown. In particular, when it is necessary to further suppress the decrease in inductance, the magnetic material thickness indicated by a straight line connecting the point of 0.3 mm at 0.1 A and the point of 0.9 mm at 2.0 A is minimized. Thickness. In this case, the inductance is maintained up to about 95% or more of the maximum value. In FIG. 3, the region is indicated by a horizontal line. The magnetic core thickness at 0.5 A, 1.0 A, and 1.5 A is as plotted in FIG. 3.
mm) and a point that becomes 0.8 mm (or 0.9 mm) at 2.0 A.

Next, an embodiment of a thin inductor will be described, and it will be described that the results of the above simulation are appropriate. The structure of the prototyped thin inductor is the same as that of FIG. A 6 mm × 6 mm × 0.3 mm (thickness) Mn—Zn ferrite core was used as the magnetic material. Also, approximately 35 μm on both sides of a 0.15 mm thick FPC board as a planar coil.
One having a conductive pattern of one layer (6 turns) made of thick copper foil was used. The measured value of the inductance of this thin inductor was 17.5 μH, which was in good agreement with the calculated value of 18.1 μH by simulation. Also,
The measured value when the conductive pattern of three turns was formed on both sides of the FPC board was 6 μH, which was in good agreement with the calculated value of 5.8 μH.

Next, a second embodiment of the thin inductor of the present invention will be described with reference to the drawings. This embodiment is a thin transformer 20. FIG. 4A is a plan view of the planar coil. However, illustration of the magnetic body is omitted. In FIG. 4A, an opening 3 is formed at the center of an insulating substrate 2 made of a resin film such as polyimide. Around the opening 3, a first coil 21 made of a conductive pattern obtained by patterning a copper foil having a thickness of about 35 μm is formed.
3 are formed. The through holes 22 and 23 are electrically connected to the through holes 24 and 25 formed at the end of the insulating substrate 2 on the lower surface. The through holes 24 and 25 are connected to external lead connection lands of the first coil 21.
A second coil 26 made of a spiral conductive pattern is formed on the periphery of the first coil 21 with a larger number of turns than the first coil 21, and a through hole 28 is formed at the end of the coil 26. The through hole 28 is electrically connected to the through hole 29 on the lower surface of the insulating substrate 2. The through hole 29 is connected to an external lead connection land of the second coil 26. On the other hand, FIG. 4B is a cross-sectional view along the CD line. A flat upper core 9 made of a magnetic material such as ferrite is disposed above the insulating substrate 2 on which the coil is formed, and a projection 1 is provided below the insulating substrate 2 at the center.
0, a lower core 13 of the same material having a protruding portion 12 on the periphery is disposed, and the protruding portion 10 is formed in the opening 3 of the insulating substrate 2.
, The end faces of the projections 10 and 12 are in close contact with the lower surface of the upper core 9, and the insulating substrate 2 is sandwiched between the cores 9 and 13 to close the magnetic circuit and improve the magnetic efficiency of the present invention. 20 basic structures are obtained. In FIG. 4, the first coil 21 and the second coil 26 are formed on the upper surface of the insulating substrate 2, but the second coil 26 may be formed on the lower surface of the insulating substrate 2. Moreover, you may arrange | position a 1st coil outside a 2nd coil. Further, as shown in FIG. 5, the first coil 21 may be provided between each turn of the second coil 26. Alternatively, the coils 4 and 5 shown in FIG. 1 may be divided and arranged in two rows, respectively, connected to different through holes, and one may be a primary coil and the other may be a secondary coil. This structure is suitable when the winding ratio is 1: 1.

In the thin transformers shown in FIGS. 4 and 5, etc., the minimum thickness of the magnetic material required for the current value is clarified in order to minimize the decrease in inductance. There is a need to provide an inexpensive thin transformer that is effectively miniaturized by preventing shortage or excessive thickness. As means for this, the minimum thickness of the flat plate portion of the core made of a magnetic material is defined in relation to the inductance and the current value. More specifically, when the current value is defined as coordinates using a horizontal axis as a current value and a vertical axis as a magnetic material thickness, when the current value is 0.1 A, the thickness is 0.2 mm (or 0.3 mm);
When the current value is 2.0 A, the thickness is 0.8 mm (or 0.9 mm).
mm) is defined as the minimum thickness of a magnetic body indicated by a straight line connecting points. With this configuration, the reduction in inductance can be suppressed by adjusting the thickness of the magnetic body to the minimum necessary thickness with respect to the current value (in the case of the numerical value in parentheses, the inductance can be further suppressed). Insufficient reduction in inductance due to insufficient thickness of the magnetic material, and unnecessary increase in size due to excessive magnetic material thickness depending on the current value are prevented. A thin inductor such as a thin transformer can be provided.

Next, as a third embodiment of the present invention,
A thin DC-DC converter made with an electric circuit of a chopper type regulator and mounted with a thin inductor (in this case, a choke coil) of the present invention will be described with reference to the drawings. The feature of this thin DC-DC converter is that the thickness of the magnetic core is optimized for the current as described above,
The insulating substrate of the thin inductor of the present invention and the circuit substrate of the DC-DC converter are integrated and shared. As shown in FIG. 6, in the thin DC-DC converter 30 of the present invention, an opening 3 is formed in a part of an insulating substrate 31 made of a double-sided FPC board such as a polyimide film having a thickness of 0.2 mm. Is formed around the thin inductor 32 of the present invention. Further, other electronic components 33 (switching elements such as FETs, capacitors, resistors, and the like) for the DC-DC converter are mounted at high density in other parts except the periphery of the opening 3.

The thin inductor 32 is formed as follows. That is, about 35 μm around the opening 3.
A first coil 4 made of a conductive pattern obtained by spirally patterning an m-thick copper foil is formed.
A second coil 5 made of a similar spiral conductive pattern is formed at a symmetrical position on the lower surface of the first coil 1. One end of each of the first coil 4 and the second coil 5 has a through hole ( No), and are electrically connected to the coils 4 and 5 so that current flows in the same direction. The other ends of the coils are electrically connected to a pair of through holes (not shown) for connecting external leads. Then, the double-sided FPC board 3 on which the coil is formed
A flat upper core 9 made of a magnetic material is disposed above the lower core 1, and a lower core 11 of the same material having a projection 10 at the center is disposed below the substrate 31. The thin inductor according to the present invention is inserted into the opening 3 of the base 31, the end face of the projection 10 is brought into close contact with the lower surface of the upper core 9, and the coil of the substrate 31 is fixed between the cores 9 and 11 with an adhesive. 32 is obtained. Note that a projection may also be formed on the peripheral edge of the magnetic core to make the upper and lower cores adhere to each other to form a closed circuit, thereby improving the magnetic efficiency. In this case, an opening through which the protrusion at the periphery is inserted is formed in the substrate in advance. In this embodiment, the coils are formed on both sides of the substrate 31. However, the coils may be formed on only one side, or the coils on one side or both sides may be laminated in two or more layers.

Here, the magnetic core uses Mn-Zn ferrite, and the thickness of the flat plate portion is, for example, with respect to a current of 0.5 A with reference to FIG. 3 as described in the first embodiment. Optimized to 0.3 mm. Plane size is 6mm x 6
mm. Therefore, the thickness d of the thin inductor 32
1 is approximately 0.9 mm, which is extremely thin. On the other hand, the electronic component having the largest height among the electronic components other than the thin inductor is the capacitor 33a, and its thickness d2 is 1.5 mm. Therefore, the distance d3 between the upper surface of the capacitor and the lower surface of the thin inductor is the thickness of the thin DC-DC converter of the present invention, which is 2 mm. Thin DC-DC of the present invention
Since the plane size of the converter 30 is within 20 mm × 10 mm, the thin DC-DC converter 30 of the present invention is used.
Fits within a volume of 20 mm × 10 mm × 2 mm (thickness).

As a result, the thin DC-DC converter 30 of the present invention can be compared with the conventional thin DC-DC converter 50 (actual open flat type 6-66291) at the same output current level.
No. 25mm x 25mm x 6mm)
(Thickness) In comparison with (thickness), the volume was reduced to about 1/9, and the size was significantly reduced. Note that, depending on the electric circuit, the same effect can be obtained by using a transformer in addition to the choke coil as the thin inductor.

The magnetic material used for the magnetic material of the thin inductor according to the present invention described in the first to third embodiments is not particularly limited. Specifically, Mn-Zn based ferrite, Ni-Zn based Ferrites such as ferrite, Cu-Zn ferrite, Mg-Zn ferrite, NiFe, NiFeCo, FeSi, FeA
Alloys such as l, FeAlSi, and FeTaN are suitable. The characteristics of the magnetic material include high saturation magnetization, high magnetic Curie temperature, stability over temperature and time, low coercivity, high magnetic permeability, and low high-frequency loss. .

The material of the insulating substrate is not particularly limited.
A resin film such as polyimide, polyester, epoxy, or PET, glass epoxy, ceramic, glass, or the like is preferable.

The material of the conductive pattern is not particularly limited, either Cu, Al, Au, Ag, Fe, Ni, Ti, V, Cr, Co.
, Mo, W, Pd, Sn, Pb and the like, a thin film using an alloy or a compound containing these elements, a thin film grown on a substrate material by vapor phase, and the like are preferable.

[0027]

According to the thin inductor of the present invention, a spiral conductor pattern is formed on one or both sides of an insulating substrate to form a coil, an opening is formed in the center of the coil, and a projection inserted through the opening. A thin inductor having an insulating substrate sandwiched from above and below by a plate-shaped magnetic material having a portion, wherein the thickness of the flat plate portion of the magnetic material is not less than a minimum thickness defined by a current value and an inductance. . With this configuration, the thickness of the magnetic body can be adjusted to the minimum required thickness for the current value to suppress the decrease in inductance. Depending on the current value, the thickness of the magnetic body becomes insufficient and the inductance decreases significantly. In addition, it is possible to prevent an unnecessary increase in the size of the magnetic body due to an excessive thickness depending on the current value, and to provide an inexpensively thin inductor that is effectively reduced in size.

Further, the thin DC-DC converter of the present invention shares the insulating circuit board of the DC-DC converter with the insulating board of the thin inductor which is a component, and
Since the thickness of the flat plate portion of the magnetic material of this thin inductor was set to be not less than the minimum thickness specified by the current value and the inductance,
Inexpensive thin DC-DC with large inductance and effective miniaturization by preventing shortage or excessive thickness of magnetic material
A converter can be provided.

[Brief description of the drawings]

FIG. 1 is a plan view and a sectional view showing a first embodiment of a thin inductor of the present invention.

FIG. 2 is a diagram showing the relationship between the inductance of a thin inductor and the thickness of a magnetic core obtained by simulation.

FIG. 3 is a diagram showing a range of a coil current and a magnetic core thickness for obtaining a large inductance of about 92% or more.

FIG. 4 is a plan view and a sectional view showing a second embodiment of the thin inductor of the present invention.

FIG. 5 is a plan view showing a modification of the second embodiment.

FIG. 6 shows a thin DC- according to a third embodiment of the present invention.
Side view including partial cross-sectional view of DC converter

FIG. 7 is a plan view of a planar coil of a conventional small inductor.

FIG. 8 is a sectional view of a conventional small inductor.

FIG. 9 is a side view including a partial cross-sectional view of a conventional thin DC-DC converter.

[Explanation of symbols]

1, 32 Thin inductor 2 Insulating substrate 3 Opening 4, 21 First coil 5, 26 Second coil 6, 8, 22, 23, 24, 25, 28, 29 Through hole 9 Upper magnetic core 10, DESCRIPTION OF SYMBOLS 12 Projection part 11, 13 Lower magnetic core 20 Thin transformer 30 Thin DC-DC converter 31 Insulating substrate of thin DC-DC converter 33 Electronic component

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H02M 3/28 H01F 31/00 DA

Claims (8)

[Claims] A coil is formed by forming a spiral conductor pattern on one or both sides of an insulating substrate, and an opening is formed at least in the center of the coil, and a flat plate having a projection inserted through the opening is provided. A thin inductor comprising a magnetic material sandwiching an insulating substrate from above and below, wherein the thickness of the flat plate portion of the magnetic material is not less than a minimum thickness determined from a current value and an inductance. 2. In coordinates where the abscissa is a current value and the ordinate is a magnetic material thickness, a point of 0.2 mm thickness when the current value is 0.1 A and a thickness of 0.2 mm when the current value is 2.0 A. 2. The thin inductor according to claim 1, wherein the thickness of the magnetic body indicated by a straight line determined from the point of 8 mm is a minimum thickness. 3. The minimum thickness is a magnetic material thickness indicated by a straight line determined by a point having a thickness of 0.3 mm when the current value is 0.1 A and a point having a thickness of 0.9 mm when the current value is 2.0 A. The thin inductor according to claim 1, wherein: 4. A coil formed by forming a spiral conductor pattern on one or both sides of an insulating circuit board of a DC-DC converter, and an opening is formed at least in the center of the coil.
A thin DC-DC converter provided with a thin inductor having an insulating circuit board sandwiched from above and below by a plate-shaped magnetic material having a projection inserted into the opening. 5. The thin DC-D according to claim 4, wherein the thickness of the flat plate portion of the magnetic material of the thin inductor is not less than a minimum thickness determined from a current value and an inductance.
C converter. 6. Coordinates in which the abscissa represents the current value and the ordinate represents the thickness of the magnetic material, a point of 0.2 mm thickness when the current value is 0.1 A, and a thickness of 0.2 mm when the current value is 2.0 A. 6. The thin DC-DC converter according to claim 5, wherein the thickness of the magnetic body indicated by a straight line connecting the points of 8 mm is the minimum thickness. 7. Coordinates where the abscissa represents the current value and the ordinate represents the thickness of the magnetic material, the point is 0.3 mm when the current value is 0.1 A, and the thickness is 0.3 mm when the current value is 2.0 A. The thin DC-DC converter according to claim 5, wherein the thickness of the magnetic body indicated by a straight line determined from the point of 9 mm is set to a minimum thickness. 8. The thin DC-DC converter according to claim 4, wherein the insulating circuit board is an FPC board.