JP6364988B2 - Planar type transformer - Google Patents

Description

  The present invention relates to a planar type transformer.

  Planar transformers (hereinafter referred to as planar transformers) can be made smaller than conventional winding transformers, and have recently begun to be used in switching power supply circuits of various information devices.

A planar transformer has a multilayer substrate in which primary and secondary winding patterns serving as main windings for power transmission are stacked with an insulating layer interposed therebetween.
By the way, in a planar transformer, an eddy current due to a leakage magnetic flux is increased because the pattern surface of the winding is wide, and the eddy current loss is larger than the resistance loss in the primary and secondary winding patterns, especially in high frequency driving. It can be a factor that reduces efficiency.

  Conventionally, in a planar transformer having no core, in order to reduce eddy current loss, an opening such as a slit is formed in the entire winding pattern.

JP-A-8-203739

  However, the resistance loss increases as the openings such as slits are formed in the winding pattern.

  According to one aspect of the invention, a multilayer substrate in which a primary winding pattern and a secondary winding pattern for performing power transmission are laminated via an insulating layer, and the primary winding pattern or the secondary winding pattern. And a core formed with a gap for suppressing magnetic saturation, and the primary winding pattern or the secondary winding pattern covered with the core. A planar type transformer is provided in which a plurality of openings are formed in a region adjacent to the gap.

  According to the disclosed planar transformer, an increase in resistance loss can be suppressed.

It is a figure which shows an example of the planar transformer by 1st Embodiment. It is an upper perspective view which shows an example of the planar transformer by 2nd Embodiment. It is a downward perspective view which shows an example of the planar transformer by 2nd Embodiment. It is sectional drawing which shows an example of the planar transformer by 2nd Embodiment. It is a figure which shows an example of the leakage magnetic flux from a gap. It is a figure which shows an example of a primary winding pattern. It is a figure which shows an example of a secondary winding pattern. It is a figure which shows the 1st example of the shape of an opening part. It is a figure which shows the 2nd example of the shape of an opening part. It is a figure which shows the 3rd example of the shape of an opening part. It is a figure which shows one structural example of the hardware of the computer used for this Embodiment. It is a figure which shows an example of the electromagnetic field analysis model of a planar transformer. It is a figure which shows an example of the magnetic flux density distribution of a primary winding pattern (the 1). It is a figure which shows an example of the magnetic flux density distribution of a primary winding pattern (the 2). It is a figure which shows an example of the relationship between the skin depth of copper, and the frequency of an electric current. It is a figure which shows an example of the relationship between ratio of total slit width and winding width, and eddy current loss. It is a figure which shows an example of the relationship between ratio of a total slit width | variety and winding width, and direct current | flow resistance and direct current | flow resistance loss. It is a figure which shows an example of the relationship between ratio of total slit width and winding width, and total loss. It is a flowchart which shows the flow of an example of the optimization process of an opening part. It is sectional drawing which shows the modification of the planar transformer by 2nd Embodiment. It is a figure which shows the position of the opening part formed in a primary winding pattern. It is a figure which shows the modification of a winding pattern.

Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 is a diagram illustrating an example of a planar transformer according to the first embodiment.

The planar transformer 1 has a multilayer substrate 2 and a core 3.
The multilayer substrate 2 has a structure in which a primary winding pattern 4 and a secondary winding pattern 5 that perform power transmission are stacked via an insulating layer 6. The multilayer substrate 2 may have a structure in which a plurality of winding patterns (primary windings, secondary windings) are stacked via a plurality of insulating layers.

  The primary winding pattern 4 is a conductor pattern formed using, for example, copper. The primary winding pattern 4 may be formed over a plurality of layers of the multilayer substrate 2, and in this case, the primary winding pattern 4 of each layer is electrically connected through a through hole or via not shown. Is done.

  The secondary winding pattern 5 is a conductor pattern formed using, for example, copper. The secondary winding pattern 5 may also be formed over a plurality of layers of the multilayer substrate 2, and in that case, the secondary winding pattern 5 of each layer is electrically connected through a through hole or via not shown. Is done.

The insulating layer 6 is an insulating layer formed by a glass epoxy substrate, for example.
The core 3 is, for example, manganese zinc (Mn—Zn) -based ferrite (magnetic material), and is disposed so as to cover at least a part of the primary winding pattern 4 and the secondary winding pattern 5 included in the multilayer substrate 2. Has been. The core 3 is provided with a gap 3g for suppressing magnetic saturation. The reason why the gap 3g is provided will be described below.

  When power transmission is performed between the primary winding pattern 4 and the secondary winding pattern 5, a closed magnetic circuit is formed inside the core 3. At this time, if the magnetic flux density of the formed closed magnetic circuit exceeds the saturation magnetic flux density of the core 3, a large current flows through the primary winding pattern 4 and the secondary winding pattern 5 and is connected to the planar transformer 1. There is a risk of damaging the switching elements that do not. Therefore, a gap 3g for reducing magnetic flux density of a closed magnetic circuit formed inside the core 3 and suppressing magnetic saturation is provided.

  By the way, when the gap 3g for suppressing magnetic saturation is provided, the leakage magnetic flux from the gap 3g may be linked to the primary winding pattern 4 and the secondary winding pattern 5 and an eddy current may be generated. Therefore, in order to reduce this eddy current, a plurality of openings as described below are formed in a part of the primary winding pattern 4 and the secondary winding pattern 5.

An example of a plurality of openings formed in a part of the primary winding pattern 4 and the secondary winding pattern 5 will be described using the primary winding pattern 4.
FIG. 1 shows a plan view of the primary winding pattern 4 as seen from the direction of arrow A in the cross-sectional view of the planar transformer 1 shown in the upper side of FIG. 1, and a plurality of openings are formed. The regions 4a and 4b of the next winding pattern 4 are indicated by hatching. Further, in order to show the positional relationship between the primary winding pattern 4 and the core 3, the arrangement region of the core 3 viewed from the direction of the arrow A is indicated by a dotted line.

  As shown in FIG. 1, in the planar transformer 1, a plurality of openings are formed in regions 4 a and 4 b adjacent to the gap 3 g of the primary winding pattern 4 covered with the core 3.

FIG. 1 shows an example in which slit-shaped openings opn1, opn2,..., Opnn extending along the direction perpendicular to the direction in which the current flows are formed.
In the planar transformer 1 according to the first embodiment, the locations where the openings opn1 to opnn are formed are limited to the regions 4a and 4b of the primary winding pattern 4 covered with the core 3 and adjacent to the gap 3g. Therefore, an increase in resistance loss can be suppressed.

  Further, as will be described later, the leakage magnetic flux from the gap 3g becomes larger as it is closer to the gap 3g and covered with the core 3. For this reason, the eddy current generated by the leakage magnetic flux is also closer to the gap 3g and further increases as it is covered by the core 3.

  In the planar transformer 1 according to the first embodiment, the generation of eddy currents can be efficiently suppressed by providing the openings opn1 to opnn in the regions 4a and 4b as described above where the leakage magnetic flux increases. That is, since the path of the eddy current generated in the primary winding pattern 4 is divided by the openings opn1 to opnn, a large eddy current is not generated. Thereby, eddy current loss can be reduced.

Although not shown, the secondary winding pattern 5 also has a plurality of openings at the same position, and the same effect can be obtained.
(Second Embodiment)
2 is an upper perspective view showing an example of a planar transformer according to the second embodiment, FIG. 3 is a lower perspective view showing an example of a planar transformer according to the second embodiment, and FIG. 4 is a second embodiment. It is sectional drawing which shows an example of the planar transformer by the form. 4 is a cross-sectional view of the planar transformer 10 shown in FIGS. 2 and 3 taken along line B. FIG.

The planar transformer 10 includes a multilayer substrate 11 and a core 12.
Similar to the multilayer substrate 2 shown in FIG. 1, the multilayer substrate 11 has a structure in which a primary winding pattern 13 and a secondary winding pattern 14 for transmitting power are stacked via an insulating layer 15. Yes.

  The core 12 has two core parts 12a and 12b. As shown in FIG. 4, the core parts 12 a and 12 b are members each having an E shape when viewed from the cross-sectional direction, and are, for example, manganese zinc (Mn—Zn) based ferrite (magnetic material). The core parts 12a and 12b are composed of inner leg portions 12a1 and 12b1, outer leg portions 12a2 and 12b2, and outer leg portions 12a3 and 12b3, and the primary winding pattern 13 and the secondary winding pattern 14 of the multilayer substrate 11 are combined. It arrange | positions so that at least one part may be covered. Further, as shown in FIG. 4, a gap between the inner leg portions 12a1 and 12b1 is formed, for example, by polishing the ends of the inner leg portions 12a1 and 12b1 to suppress magnetic saturation. 12c is provided. In FIG. 4, the closed magnetic path is indicated by arrows mg1, mg2, mg3, and mg4.

The reason why the gap 12c is provided is as described above.
When such a gap 12c is provided, the leakage magnetic flux from the gap 12c may be linked to the primary winding pattern 13 or the secondary winding pattern 14 and an eddy current may be generated. Hereinafter, this phenomenon will be described with reference to FIG.

  FIG. 5 is a diagram illustrating an example of leakage magnetic flux from the gap. FIG. 5 is an enlarged view of the region a1 of the planar transformer 10 shown in FIG. 4, and the same elements as those shown in FIG.

  In FIG. 5, the leakage magnetic flux from the gap 12c is indicated by a dotted arrow. The leakage magnetic flux from the gap 12 c is linked to the primary winding pattern 13 and the secondary winding pattern 14, so that an eddy current is generated in the primary winding pattern 13 and the secondary winding pattern 14. Further, the leakage magnetic flux is closer to the gap 12c and further increases as it is covered by the core components 12a and 12b. Therefore, the eddy current generated in the primary winding pattern 13 and the secondary winding pattern 14 is also close to the gap 12c and further increases in the portion covered with the core components 12a and 12b. Therefore, in order to reduce this eddy current, a plurality of openings as described below are formed in a part of the primary winding pattern 13 and the secondary winding pattern 14.

  FIG. 6 is a diagram illustrating an example of a primary winding pattern, and FIG. 7 is a diagram illustrating an example of a secondary winding pattern. 6 and 7 are plan views of the primary winding pattern 13 and the secondary winding pattern 14 as seen from the direction of arrow C shown in FIG. The regions 13a, 13b, 14a, 14b of the primary winding pattern 13 and the secondary winding pattern 14 in which a plurality of openings are formed are indicated by hatching. Also, in order to show the positional relationship between the primary winding pattern 13, the secondary winding pattern 14 and the core parts 12a and 12b, the core parts 12a and 12b, the inner leg parts 12a1 and 12b1, and the outer leg parts as seen from the direction of the arrow C. The arrangement region of 12a2, 12a3, 12b2, and 12b3 is indicated by a dotted line.

The dotted lines E and G and the points p1 and p2 shown in FIG. 6 will be described later.
6 and 7, the formation region of the gap 12c provided between the inner leg portions 12a1 and 12b1 corresponds to the arrangement region of the inner leg portions 12a1 and 12b1 indicated by dotted lines. As described above, the eddy current is more likely to occur in the portion closer to the gap 12c and further covered with the core parts 12a and 12b.

  In the planar transformer 10 of the second embodiment, a plurality of openings are formed in the regions 13a, 13b, 14a, and 14b of the primary winding pattern 13 and the secondary winding pattern 14 in which such eddy currents are likely to occur. Has been. Thereby, the path of the eddy current generated in the primary winding pattern 13 and the secondary winding pattern 14 is divided by the plurality of openings, so that a large eddy current is not generated.

  Hereinafter, examples of the shape of the plurality of openings formed in the primary winding pattern 13 will be described with reference to FIGS. A plurality of openings formed in the secondary winding pattern 14 can be similarly shaped.

FIG. 8 is a diagram illustrating a first example of the shape of the opening.
In FIG. 8, the openings opna1, opna2,..., Opnan formed in the primary winding pattern 13 have a slit shape extending along the direction perpendicular to the direction in which the current flows. The width of the conductor portion of the primary winding pattern 13 is W1, the width of the openings opna1 to opnan is I1, and the length of the openings opna1 to opnan is L1.

FIG. 9 is a diagram illustrating a second example of the shape of the opening.
9, the openings opnb1, opnb2,..., Opnbn formed in the primary winding pattern 13 have a mesh shape formed in a lattice shape. The width of the conductor portion of the primary winding pattern 13 is W2, the width of the openings opnb1 to opnbn is I2, and the length of the openings opnb1 to opnbn is L2.

FIG. 10 is a diagram illustrating a third example of the shape of the opening.
In FIG. 10, the openings opnc1, opnc2,..., Opncn formed in the primary winding pattern 13 have a slit shape extending along the direction in which the current flows. Further, the width of the conductor portion of the primary winding pattern 13 is W3, the width of the openings opnc1 to opncn is I3, and the length from the surface of the primary winding pattern 13 in the region where the openings opnc1 to opncn are formed is L3.

  As described above, in the planar transformer 10, a plurality of openings are formed adjacent to the gap 12c of the primary winding pattern 13 and the secondary winding pattern 14 covered with the core components 12a and 12b. It is limited to the areas 13a, 13b, 14a, and 14b. Therefore, an increase in resistance loss can be suppressed.

  Further, by providing a plurality of openings in the regions 13a, 13b, 14a, and 14b as described above where the leakage magnetic flux (eddy current) increases, the generation of eddy current can be efficiently suppressed. That is, since the path of the eddy current generated in the primary winding pattern 13 and the secondary winding pattern 14 is divided by the plurality of openings, a large eddy current is not generated. Thereby, eddy current loss can be reduced.

Next, an optimization processing method for determining an appropriate formation position and size of the opening will be described.
The following optimization processing is performed on a computer when designing a planar transformer.

  FIG. 11 is a diagram illustrating a configuration example of computer hardware used in the present embodiment. The entire computer 20 is controlled by a processor 21. The processor 21 is connected to a RAM (Random Access Memory) 22 and a plurality of peripheral devices via a bus 29. The processor 21 may be a multiprocessor. The processor 21 is, for example, a central processing unit (CPU), a micro processing unit (MPU), a digital signal processor (DSP), an application specific integrated circuit (ASIC), or a programmable logic device (PLD). The processor 21 may be a combination of two or more elements among CPU, MPU, DSP, ASIC, and PLD.

  The RAM 22 is used as a main storage device of the computer 20. The RAM 22 temporarily stores at least part of an OS (Operating System) program and application programs to be executed by the processor 21. The RAM 22 stores various data necessary for processing by the processor 21.

  Peripheral devices connected to the bus 29 include an HDD (Hard Disk Drive) 23, a graphic processing device 24, an input interface 25, an optical drive device 26, a device connection interface 27, and a network interface 28.

  The HDD 23 magnetically writes and reads data to and from the built-in disk. The HDD 23 is used as an auxiliary storage device of the computer 20. The HDD 23 stores an OS program, application programs, and various data. As the auxiliary storage device, a semiconductor storage device such as a flash memory can be used.

  A monitor 24 a is connected to the graphic processing device 24. The graphic processing device 24 displays an image on the screen of the monitor 24a in accordance with an instruction from the processor 21. Examples of the monitor 24a include a display device using a CRT (Cathode Ray Tube) and a liquid crystal display device.

  A keyboard 25 a and a mouse 25 b are connected to the input interface 25. The input interface 25 transmits a signal sent from the keyboard 25a and the mouse 25b to the processor 21. The mouse 25b is an example of a pointing device, and other pointing devices can also be used. Examples of other pointing devices include a touch panel, a tablet, a touch pad, and a trackball.

  The optical drive device 26 reads data recorded on the optical disc 26a using a laser beam or the like. The optical disk 26a is a portable recording medium on which data is recorded so that it can be read by reflection of light. The optical disk 26a includes a DVD (Digital Versatile Disc), a DVD-RAM, a CD-ROM (Compact Disc Read Only Memory), a CD-R (Recordable) / RW (ReWritable), and the like.

  The device connection interface 27 is a communication interface for connecting peripheral devices to the computer 20. For example, the device connection interface 27 can be connected to a memory device 27a and a memory reader / writer 27b. The memory device 27 a is a recording medium equipped with a communication function with the device connection interface 27. The memory reader / writer 27b is a device that writes data to the memory card 27c or reads data from the memory card 27c. The memory card 27c is a card-type recording medium.

  The network interface 28 is connected to the network 28a. The network interface 28 transmits / receives data to / from other computers or communication devices via the network 28a.

With the hardware configuration as described above, optimization processing can be realized.
The computer 20 implements the processing functions of the second embodiment by executing a program recorded on a computer-readable recording medium, for example. A program describing the processing contents to be executed by the computer 20 can be recorded in various recording media. For example, a program to be executed by the computer 20 can be stored in the HDD 23. The processor 21 loads at least a part of the program in the HDD 23 into the RAM 22 and executes the program. A program to be executed by the computer 20 can also be recorded on a portable recording medium such as the optical disk 26a, the memory device 27a, and the memory card 27c. The program stored in the portable recording medium becomes executable after being installed in the HDD 23 under the control of the processor 21, for example. The processor 21 can also read and execute the program directly from the portable recording medium.

(Optimization process)
In the optimization process, first, the computer 20 performs electromagnetic field analysis on the planar transformer to be designed.

  FIG. 12 is a diagram illustrating an example of an electromagnetic field analysis model of a planar transformer. In FIG. 12, the planar transformer to be analyzed is assumed to be the same as the planar transformer 10 shown in FIGS. 2 to 4, and is given the same reference numerals.

  The wirings 16a, 16b, 17a, and 17b are wirings set on the computer 20 in the electromagnetic field analysis. The wiring 16 a is connected to one end of the primary winding pattern 13, and the wiring 16 b is connected to the other end of the primary winding pattern 13. The wiring 17a is connected to one end of the secondary winding pattern 14 (see FIG. 3), and the wiring 17b is connected to the other end of the secondary winding pattern 14.

An electromagnetic field analysis is performed on such an electromagnetic field analysis model.
As described above, the eddy current is generated when the leakage magnetic flux is linked to the winding pattern (the primary winding pattern 13 or the secondary winding pattern 14). Therefore, an example in which the magnitude of the leakage magnetic flux is calculated by electromagnetic field analysis is shown below.

  13 and 14 are diagrams showing an example of the magnetic flux density distribution of the primary winding pattern. The simulation conditions are as follows. The width of the primary winding pattern 13 is 1.1 mm, the thickness is 0.07 mm, the number of turns is 4, and the width of the secondary winding pattern 14 is 2.37 mm, the thickness is 0.07 mm, and the number of turns is 2. The insulating layer 15 is a glass epoxy substrate, the primary side effective current is 2 A, and the frequency of the current is 10 MHz.

  FIG. 13 shows an example of the magnetic flux density distribution on the dotted line E of the primary winding pattern 13 shown in FIG. That is, the horizontal axis indicates the position on the dotted line E, and the vertical axis indicates the magnetic field of the vertical component (corresponding to the leakage flux) with respect to the primary winding pattern 13 at the position on the dotted line E.

  Further, 0 mm on the horizontal axis indicates the position of the point p1 on the dotted line E shown in FIG. 6 (the center point of the region surrounded by the primary winding pattern 13 where the primary winding pattern 13 is not disposed). A range indicated by an arrow F in FIG. 13 indicates a range in which the gap 12c is disposed.

  From FIG. 13, the leakage magnetic flux from the core 12 that causes eddy current generation is larger as it is closer to the gap 12c and is smaller as it is farther from the gap 12c. In the example of FIG. 13, the magnetic field becomes the largest at a position of ± 3 mm, and when it exceeds ± 4 mm, the magnetic field greatly decreases. Therefore, when the result shown in FIG. 13 is obtained, it can be seen that the effect of forming the opening at a position 4 mm or more away from the point p1 with respect to the primary winding pattern 13 is low.

  On the other hand, FIG. 14 shows an example of the magnetic flux density distribution on the dotted line G of the primary winding pattern 13 shown in FIG. The horizontal axis indicates the position on the dotted line G, and the vertical axis indicates the magnetic field of the vertical component with respect to the primary winding pattern 13 at the position on the dotted line G. Further, 0 mm on the horizontal axis indicates the position of the point p2 on the dotted line G shown in FIG.

  As shown in FIG. 6, in the primary winding pattern 13, the portion indicated by the dotted line G is a portion not covered with the core 12, and it can be seen that the leakage magnetic flux is small as shown in FIG. 14. Thereby, it turns out that the effect which forms an opening part in the part which is not covered with the core 12 of the primary winding pattern 13 is low.

  Based on the above electromagnetic field analysis results, the length in the pattern width direction of the primary winding pattern 13 in the regions 13a and 13b (for example, L1 to L3 in FIGS. 8 to 10) is optimized. For example, the locations where the regions 13a and 13b are formed are optimized by not providing openings in portions where the effect of forming a plurality of openings is low (portions where the effect of suppressing the generation of eddy currents is low). Thereby, the increase in resistance loss can be suppressed more appropriately.

The same effect can be obtained by optimizing the length of the secondary winding pattern 14 in the pattern width direction of the regions 14a and 14b of the secondary winding pattern 14 in the same manner.
Next, an example of a method for calculating the skin depth, eddy current loss, DC resistance loss and determining the size of the opening by the computer 20 will be described.

  When high-frequency current flows through the conductor, the current density on the conductor surface increases as the current frequency increases. This phenomenon is called the skin effect. Further, the depth from the surface of the conductor through which the current flows is called skin depth, and is represented by the following formula (1).

Skin depth = √ (1 / (πfμδ)) (1)
In equation (1), f is the current frequency, μ is the magnetic permeability of the conductor, and δ is the conductivity of the conductor.
FIG. 15 is a diagram illustrating an example of the relationship between the copper skin depth and the current frequency.

The horizontal axis represents the current frequency, and the vertical axis represents the copper skin depth. In formula (1), the skin depth of copper when μ = π × 10 ⁻⁷ H / m (copper permeability) and δ = 5.8 × 10 ⁷ S / m (copper conductivity) are applied. The relationship with current frequency is shown in FIG.

  When the planar transformer 10 is a switching transformer, the primary winding pattern 13 or the secondary winding pattern 14 has a high-frequency current corresponding to the resonance frequency of the planar transformer 10 when the current rises or falls due to a switching operation. Ingredients appear. The resonance frequency is, for example, about 100 times the switching frequency. This high frequency current component corresponds to an eddy current.

  For example, when the primary winding pattern 13 or the secondary winding pattern 14 is copper and the frequency f is 10 MHz, the skin depth is 21 μm from FIG. That is, an eddy current flows in a range of 21 μm from the surface of the primary winding pattern 13 or the secondary winding pattern 14.

  Therefore, for example, in the primary winding pattern 13, the eddy current can be reduced by making the widths W1 to W3 of the conductor portions shown in FIGS. 8 to 10 smaller than 21 μm (skin depth). The same applies to the secondary winding pattern 14.

  Next, eddy current loss and DC resistance loss will be described. When a plurality of openings are formed in the primary winding pattern 13 or the secondary winding pattern 14, the eddy current path is divided by the openings, so that eddy current loss is reduced. However, since the cross-sectional area in the direction in which the winding current flows is reduced by forming the opening, the DC resistance loss increases.

Hereinafter, a method for determining an appropriate opening size and the like from a range in which the total loss of the eddy current loss and the DC resistance loss with respect to the shape of the opening is minimized will be described.
In the following description, slit-like openings opnc1 to opncn extending along the direction of current flow as shown in FIG. 10 will be described as an example. For convenience, a case will be described in which slits are provided at equal intervals in the winding width of the winding pattern (primary winding pattern 13 or secondary winding pattern 14), and further, the slits are provided in the entire winding pattern. . Even when a slit is formed in a part of the winding pattern, it can be calculated in the same manner as described below. For example, when the openings opnc1 to opncn are formed in a part of the primary winding pattern 13, the length (L) of the primary winding pattern 13 in Formula (1) and Formula (2) shown below The winding width (pattern width) may be set according to the size of the regions 13a and 13b.

(Eddy current loss calculation example)
FIG. 16 is a diagram illustrating an example of the relationship between the ratio of the total slit width and the winding width and the eddy current loss. The horizontal axis represents the total slit width / winding width. The total slit width is, for example, the sum of the widths I3 in the openings opnc1 to opncn illustrated in FIG. 10, and the winding width is the pattern width of the primary winding pattern 13 or the secondary winding pattern 14. The vertical axis represents the eddy current loss of one layer of the winding pattern.

The eddy current loss is calculated by the following equation (2).
Eddy current loss (W / m ³ ) = π ² Bm ² f ² d ² / 6ρ (2)
In equation (2), Bm is the maximum magnetic flux density, f is the current frequency, ρ is the resistivity of the conductor, and d is the wiring width (width I3 in the example of FIG. 10). Moreover, the calculation conditions of the eddy current loss shown in FIG. 16 are the maximum magnetic flux density (Bm = 20 mT), the frequency (f = 10 MHz), and the resistivity of copper (ρ = 1.68 × 10 ⁻⁸ Ωm). Here, the maximum magnetic flux density Bm can be estimated from electromagnetic field analysis or the like, and the frequency f is the same as f in the equation (1).

  As shown in FIG. 16, it can be seen that the eddy current loss decreases as the total slit width increases with respect to the winding width. Further, from FIG. 16, when the ratio of the total slit width to the winding width is 0.3, the eddy current loss of one winding pattern layer is about 0.15W. Therefore, when the winding pattern (the primary winding pattern 13 and the secondary winding pattern 14) is formed over 10 layers in the planar transformer 10, the eddy current loss is found to be 1.5W.

  When the openings opna1 to opnan as shown in FIG. 8 are employed, for example, the lengths of the regions 13a and 13b of the primary winding pattern 13 (length in the pattern length direction) and the widths of the openings opna1 to opnan Calculate the eddy current loss relative to the ratio of the total value of I1.

  When the openings opnb1 to opnbn as shown in FIG. 9 are employed, for example, the ratio of the area of the regions 13a and 13b of the primary winding pattern 13 to the total value of the areas of the openings opnc1 to opncn Calculate the eddy current loss.

(DC resistance loss calculation example)
FIG. 17 is a diagram illustrating an example of the relationship between the ratio between the total slit width and the winding width, and the DC resistance and DC resistance loss.

  The horizontal axis represents the total slit width / winding width. The total slit width is the sum of the slit widths (for example, width I3) shown in FIG. 10, for example, as in FIG. The left vertical axis represents the DC resistance of one layer of the winding pattern, and the right vertical axis represents the DC resistance loss of one layer of the winding pattern.

A waveform R1 in FIG. 17 indicates a DC resistance. A waveform R2 in FIG. 17 indicates a direct current resistance loss, and is calculated by using the following equation (3).
DC resistance loss (W) = I ² R = I ² ρL / S (3)
In Expression (3), I is an effective current, R is a DC resistance, ρ is a resistivity of a conductor, L is a length of a winding pattern, and S is a cross-sectional area of the winding pattern. The calculation conditions are as follows.

The effective current is I = 2A, the resistivity of copper is ρ = 1.68 × 10 ⁻⁸ Ωm, the length of the winding pattern is L = 238 mm, the cross-sectional area is S = the thickness of the winding pattern ( 0.07 mm) × (winding width (1.1 mm) −total slit width).

  As shown by the waveform R2 in FIG. 17, it can be seen that the DC resistance loss increases as the total slit width increases with respect to the winding width. Moreover, from FIG. 17, when the ratio of the total slit width to the winding width is 0.3, the DC resistance loss of one winding pattern layer is 0.3W. Therefore, for example, when the winding pattern is formed over 10 layers in the planar transformer 10, the DC resistance loss is 3W.

  When the openings opna1 to opnan as shown in FIG. 8 are employed, for example, with respect to the ratio between the winding width and the width of the regions 13a and 13b of the primary winding pattern 13 (for example, L1 in FIG. 8), Calculate DC resistance loss.

When the openings opnb1 to opnbn as shown in FIG. 9 are employed, the DC resistance loss is calculated with respect to the ratio between the winding width and, for example, L2 in FIG.
Next, the total loss of eddy current loss and DC resistance loss will be described.

(Example of calculating total loss)
FIG. 18 is a diagram illustrating an example of the relationship between the ratio between the total slit width and the winding width and the total loss.
The horizontal axis represents the total slit width / winding width. The total slit width is the sum of the slit widths (for example, width I3) shown in FIG. 10, for example, as in FIG. The vertical axis represents the total loss of one winding pattern layer.

  A waveform IL in FIG. 18 indicates the eddy current loss shown in FIG. Moreover, the waveform R2 of FIG. 18 is a waveform which shows the DC resistance loss shown in FIG. A waveform TL is a waveform indicating the total loss obtained by adding the eddy current loss and the DC resistance loss.

  As indicated by the waveform TL in FIG. 18, the total loss is relatively low in the range indicated by the arrow K. From the waveform TL in FIG. 18, the ratio of the total slit width and the winding width that minimizes the total loss of the winding pattern 1 layer to 0.82 W is 0.32. Here, when the ratio between the total slit width and the winding width is selected as 0.32, and the wiring width (width W3 in FIG. 10) is selected as 20 μm in consideration of the skin effect, a conductor having a winding width of 1.1 mm is selected. If slits are provided in the pattern at equal intervals, the slit width can be determined to be 0.01 mm. Thus, the size (slit width, etc.) and the number of slits of the plurality of openings opnc1 to opncn can be optimized.

  Similarly, when the openings opna1 to opnan and opnb1 to opnbn as shown in FIG. 8 and FIG. Optimize the size etc.

By determining the size of the plurality of openings based on the skin depth and the total loss of eddy current loss and DC resistance loss, the loss can be reduced appropriately.
Hereinafter, a flow of an example of processing for optimizing a plurality of openings to be formed is summarized in a flowchart.

  FIG. 19 is a flowchart illustrating an exemplary flow of an opening optimization process. The following processing is described as being performed under the control of the processor 21 of the computer 20 shown in FIG.

  First, the processor 21 acquires the physical characteristics and usage conditions of the planar transformer input from the user (step S1). The physical characteristics of the planar transformer are, for example, the shape of the core of the planar transformer, the characteristics of the winding pattern (length, thickness, width, number of turns), and the like. The usage conditions of the planar transformer are, for example, a circuit system in which the planar transformer is used, a voltage, a current, a frequency, and the like used in the circuit.

  Next, the processor 21 calculates a magnetic flux density distribution on the winding pattern (step S2). For example, the processor 21 obtains the magnetic flux density distribution as shown in FIGS. 12 and 13 by electromagnetic field analysis or the like. And the processor 21 determines the area | region which forms an opening part based on the part with high magnetic flux density on a winding pattern.

  Thereafter, the processor 21 calculates the skin depth (step S3), calculates the eddy current loss (step S4), calculates the DC resistance loss (step S5), and calculates the total loss (step S6). Then, an appropriate position and size of the opening are determined (step S7). In the process of step S7, as described above, for example, when the opening has a slit shape as shown in FIG. 10, the total slit width / winding width is selected from the range where the total loss is minimized. Furthermore, considering the width W3 to be narrower than the skin depth, the slit width, the interval at which the slit is inserted into the winding pattern, and the like are determined.

Note that the order of the processes in steps S2 to S5 may be appropriately changed.
By the way, the position of the gap for suppressing magnetic saturation is not limited between the inner leg portions of the core but may be between the outer leg portions. Hereinafter, the example is demonstrated as the modification 1 of the planar transformer by 2nd Embodiment.

(Modification 1)
FIG. 20 is a cross-sectional view showing a modification of the planar transformer according to the second embodiment.
The planar transformer 30 includes a multilayer substrate 31 and a core 32.

Similar to the multilayer substrate 2 shown in FIG. 1, the multilayer substrate 31 has a structure in which a primary winding pattern 33 and a secondary winding pattern 34 for transmitting power are stacked via an insulating layer 35. Yes.
The core 32 has two core parts 32a and 32b, like the core 12 shown in FIG. However, unlike the core 12, the core 32 is not between the inner legs 32a1 and 32b1, but between the outer legs 32a2 and 32b2 and between the outer legs 32a3 and 32b3. 32d is provided.

  When the core 32 having such gaps 32c and 32d is used, a plurality of openings of the primary winding pattern 33 and the secondary winding pattern 34 are formed at positions as shown below. In the following, an example of a plurality of openings formed in the primary winding pattern 33 will be described, but a plurality of openings formed in the secondary winding pattern 34 are also formed at the same position.

FIG. 21 is a diagram showing the position of the opening formed in the primary winding pattern.
FIG. 21 is a plan view of the primary winding pattern 33 viewed from the direction of arrow J shown in FIG. 20, and regions 33a and 33b of the primary winding pattern 33 in which a plurality of openings are formed are hatched. It is shown in In addition, in order to show the arrangement relationship between the primary winding pattern 33 and the core parts 32a and 32b, the arrangement area of the core 32 part a, the inner leg part 32a1, and the outer leg parts 32a2 and 32a3 viewed from the direction of the arrow J is indicated by a dotted line. It is shown.

  The formation region of the gap 32c provided between the outer leg portions 32a2 and 32b2 shown in FIG. 20 corresponds to the arrangement region of the outer leg portion 32a2 indicated by the dotted line in FIG. Further, the formation region of the gap 32d provided between the outer leg portions 32a3 and 32b3 shown in FIG. 20 corresponds to the arrangement region of the outer leg portion 32a3 indicated by the dotted line in FIG.

  Leakage magnetic flux from the gaps 32c and 32d is closer to the gaps 32c and 32d and further increases as it is covered by the core 32. For this reason, the eddy current generated by the leakage magnetic flux is also closer to the gaps 32 c and 32 d and further increases as the portion is covered by the core 32. Since the core 32 of the planar transformer 30 is provided with two gaps 32c and 32d as shown in FIG. 20, there are two portions where a large eddy current is generated in the primary winding pattern 33. .

  Therefore, the primary winding pattern 33 is formed with a plurality of openings at two portions where a large eddy current is generated. That is, a plurality of openings are formed in the regions 33 a and 33 b of the primary winding pattern 33 that are adjacent to the gaps 32 c and 32 d (arrangement regions of the outer legs 32 a 2 and 32 a 3) and are covered with the core 32. . Thereby, the path of the eddy current generated in the primary winding pattern 33 is divided by the plurality of openings, so that a large eddy current does not occur.

  As the shape of the opening, the openings opna1 to opnan, opnb1 to opnbn, and opnc1 to opncn as shown in FIGS. 8 to 10 can be used. The size and the like of the opening are determined based on the total value of the eddy current loss and the DC resistance loss as described above.

  As described above, in the planar transformer 30, a plurality of openings are formed adjacent to the gaps 32c and 32d of the primary winding pattern 33 and the secondary winding pattern 34 covered with the core parts 32a and 32b. The area is limited. Therefore, an increase in resistance loss can be suppressed.

  In addition, by providing a plurality of openings in the region where the leakage magnetic flux (eddy current) increases, the generation of eddy current can be efficiently suppressed. That is, since the path of the eddy current generated in the primary winding pattern 33 and the secondary winding pattern 34 is divided by the plurality of openings, a large eddy current is not generated. Thereby, eddy current loss can be reduced.

  In addition to the gaps 32c and 32d between the outer legs 32a2 and 32b2 or the outer legs 32a3 and 32b3, the core 32 has a gap for suppressing magnetic saturation between the inner legs 32a1 and 32b1. May be. In such a case, in addition to the openings described above, a plurality of openings are provided in the region of the primary winding pattern 33 and the secondary winding pattern 34 that are adjacent to the gap of the inner leg portion and covered with the core. You may make it form.

(Modification 2)
FIG. 22 is a diagram illustrating a modification of the winding pattern.
In FIG. 22, the core 41 is represented by a dotted line. In the winding pattern (primary winding pattern or secondary winding pattern) 40 shown in FIG. 22, illustration of a region where a plurality of openings are formed is omitted.

  In the winding pattern 40, the pattern width wa of the portion not covered with the core 41 is narrower than the pattern width wb of the portion covered with the core 41. In the portion not covered by the core 41, the coupling ratio between the primary winding pattern and the secondary winding pattern of the planar transformer is low, and eddy current loss occurs although it does not contribute much to the performance of the planar transformer ( Smaller than the portion covered by the core 41).

  As shown in FIG. 22, by reducing the pattern width wa of the portion not covered by the core 41, the winding pattern 40 of the portion not covered by the core 41 can be brought closer to the core 41, and the coupling rate is improved. it can. Moreover, eddy current loss can be reduced by reducing the pattern width wa. Furthermore, the planar transformer can be miniaturized.

  Such a winding pattern 40 may be applied as the primary winding patterns 4, 13, 33 of the planar transformers 1, 10, 30 described above or the secondary winding patterns 5, 14, 34.

  As described above, one aspect of the planar transformer of the present invention has been described based on the embodiment, but these are merely examples, and the present invention is not limited to the above description.

DESCRIPTION OF SYMBOLS 1 Planar transformer 2 Multilayer substrate 3 Core 3g Gap 4 Primary winding pattern 4a, 4b Area | region 5 Secondary winding pattern 6 Insulation layer opn1-opnn Opening

Claims (4)

A multilayer substrate in which a primary winding pattern and a secondary winding pattern for performing power transmission are laminated via an insulating layer;
A core disposed so as to cover at least a part of the primary winding pattern or the secondary winding pattern and having a gap for suppressing magnetic saturation;
The primary winding pattern or the primary winding pattern or the secondary winding pattern covered with the core includes only the one side surface adjacent to the gap among the two side surfaces of each of the primary winding pattern and the secondary winding pattern. A planar transformer having a plurality of openings formed only in the region of the secondary winding pattern .   The width of the conductor portion of the primary winding pattern or the secondary winding pattern in the region is smaller than the skin depth of the primary winding pattern or the secondary winding pattern. The planar type transformer described in 1.   The size of the plurality of openings in the primary winding pattern or the secondary winding pattern includes an eddy current loss that decreases as the size increases, and a DC resistance that increases as the size increases. 3. The planar transformer according to claim 1, wherein the planar transformer is determined based on a total loss obtained by adding the loss. The first pattern width of the primary winding pattern or the secondary winding pattern not covered by the core is the first pattern width of the primary winding pattern or the secondary winding pattern covered by the core. 4. The planar transformer according to claim 1, wherein the planar transformer is narrower than a pattern width of 2. 5.

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