JPH06236821A - Film type transformer - Google Patents

Abstract

(57) [Abstract] [Purpose] Utilizing the skin effect of the winding conductor to obtain good magnetic coupling between the primary and secondary windings without using a magnetic material, and it is small, thin and lightweight. Try to change. [Structure] A plurality of film type transformers each having a primary winding pattern and a secondary winding pattern formed adjacent to each other on a thin film substrate are laminated, and a primary winding pattern and a secondary winding pattern of each layer are formed. It is characterized in that they are connected in series or in parallel so that good magnetic coupling between the primary and secondary windings can be obtained without using a magnetic material by utilizing the skin effect of the winding conductor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film type transformer in which a primary coil and a secondary coil pattern are formed on a film-shaped thin film substrate.

[0002]

2. Description of the Related Art Generally, among various power supply devices, those having a medium capacity (several kW) or more, such as for driving a motor, are often manufactured independently as a single product, but several hundred or several tens of W The following items are often incorporated in a product system such as a personal computer.
Particularly in computer power supplies, signal semiconductors, that is, memory devices, have been dramatically reduced in size and density, and the percentage of power supplies on a printed circuit board has been increasing in recent years. Against this background, there is a demand for smaller and lighter small-capacity power supplies.

[0003]

On the other hand, with the recent increase in the frequency of power semiconductor elements, miniaturization of transformers, inductors, and capacitors has been realized. However, reducing the loss of these circuit components at high frequencies is an important issue, and the use of ferrite or amorphous magnetic material for the magnetic core of the inductor and transformer corresponds to the reduction of loss at high frequencies. However, also in these magnetic materials, so-called iron loss increases with the excitation frequency, which is a factor that reduces the efficiency of the power supply device. Further, the magnetic material essentially has a saturated state of magnetic flux, and the magnetic flux value that can be used as an inductor and a transformer, that is, the product of voltage and time, is limited, which is a constraint condition for device design. In order to solve such problems, it is necessary to develop an air-core transformer, which is the ultimate transformer.

The present invention has been made in view of the above circumstances, and good magnetic coupling between primary and secondary windings can be obtained by utilizing the skin effect of a winding conductor without using a magnetic material. Thus, it is an object of the present invention to provide a film type transformer which can be made small, thin and lightweight.

[0005]

Therefore, in the film type transformer of the present invention, good magnetic coupling between the primary and secondary windings can be achieved by utilizing the skin effect of the winding conductor without using a magnetic material. The present invention is characterized in that it is provided with a primary winding pattern and a secondary winding pattern that are formed close to each other on a thin film substrate. Further, the present invention is to laminate a plurality of film type transformers each having a primary winding pattern and a secondary winding pattern, which are formed close to each other on a thin film substrate, to form a primary winding pattern and a secondary winding of each layer. The feature is that the patterns are connected in series or in parallel.

[0006]

The film type transformer of the present invention forms a thin film transformer by forming primary and secondary coil patterns of the transformer on the film thin film substrate, and even one sheet can operate the transformer. However, a plurality of thin film transformers may be stacked to improve low frequency characteristics, match impedance with a load, provide a plurality of input / output terminals, change a transformation ratio, and the like. Structurally, since a transformer is created on a single thin film substrate in this way, it is used for power supplies for personal computers, word processors, mobile phones, and other electronic devices that need to be compact and lightweight, and for applications such as mounting satellites. Can be expected.

In terms of cost, it is possible to mass-produce inexpensively by using printing technology, etching technology and lithographic technology. As for the electrical characteristics, the high frequency characteristics are good, the low frequency characteristics are improved as the number of laminated layers is increased, and the low frequency characteristics are further improved by using a thin film magnetic material or magnetic powder together, and it can be used at commercial frequencies. A thin film power supply and a card power supply can be put into practical use by changing the circuit connection and simultaneously creating another electronic circuit without changing the impedance or providing a plurality of input / output terminals.

[0008]

First, the basic principle of the present invention will be described.
FIG. 7A shows a principle diagram of a conventional transformer using a magnetic material for the magnetic core. The main magnetic flux φ _m is commonly linked to the primary and secondary windings, while the leakage fluxes φ ₁₁ and φ ₁₂ are the same windings as the current-carrying windings that cause the magnetic flux near each winding. Only crossed. These leakage fluxes are
This occurs because the geometrical distance between the subsequent windings is large, and can be reduced by reducing the distance between both windings as shown in FIG. 7B. When the excitation frequency is further increased, the current inside the conductor is concentrated and distributed on the conductor surface due to the skin effect, and the magnetic flux inside each conductor, which is the leakage flux of each conductor, is reduced, and the primary and secondary The coupling coefficient of the winding is improved. This is the basic operation principle of the transformer of the present invention, and when the excitation frequency becomes several tens of kHz or more when the diameter of the conductor cross section is several hundreds μm, there is no magnetic core, that is, in air (permeability μ ₀ = 4π × 10 ⁻⁷ ( H / m))
It has been confirmed that the coupling coefficient is 70% or more.

Next, for the sake of simplicity, the skin effect of a circular cross section will be described. As shown in FIG. 8, a radius a and a length l ₁
When the current i is flowing in the conductor of, the governing equation for the current density J on the conductor cross section is (l / r) ∂ (r · (∂J / ∂r)) / ∂r = (μ ₀ / ρ) ∂J / ∂t ... (1) However, r, t, and ρ represent the coordinate time in the radial direction and the resistivity of the conductor, respectively. The solution of this type of governing equation for a circular boundary is represented by the Bessel function: J (r) = (k ₁ I / 2πa) {(I ₀ (k ₁ r) / I ₀ ′ (k ₁ a)} exp (jωt) ... (2) where I ₀ (k ₁ r) is the 0th floor first
It is a modified Bessel function of a kind, and k ₁ = a (ωμ ₀ π / 2ρ) ^1/2 (3) where ω is the angular frequency of the current. Further, I ₀ ′ represents the differential function of I _{0 in} the radial direction, and the time derivative ∂ / ∂t on the right side of the equation (1) was determined as jω.

First, considering only the internal magnetic flux as the conductor of FIG. 8, the potential difference V across the conductor surface is V = ρI ₁ J (a) = ρl ₁ (k because the conductor surface current is interlinked with the internal magnetic flux. ₁ I / 2πa) {(I ₀ (k ₁ a) / I ₀ ′ (k ₁ a)} ... (4) On the other hand, the AC resistance and internal inductance of the conductor of FIG. R _A1 and L
When _{it, V = (R A1 +} jωL it) I ...... it is (5). Here, I = ∫ ₀ ^a J · 2πr · dr (6) From the expressions (2) and (5), (1 / R _D1 ) (R _A1 + jωL _it ) = (k ₁ a / 2) {I ₀ (k ₁ a) / I ₀ ^, (k ₁ a)} ...... (7) is obtained. Here, R _D1 is the direct current resistance of the conductor, and R _D1 = ρl ₁ / (πa ² ) ... (8).

Since the real part and the imaginary part of the equation (7) are equal to each other, when k ₁ <l, R _A1 ≈R _D1 {l + (1/3) k ₁ ⁴ } ... (9) L _i1 ≈ ( _{μ 0 l 1/2) {} l- (1/6) k 1 4} ...... (10) in addition, when _{k 1 ≧ 1, R A1 ≒} R D1 {(1/4) + k 1 + (l / ^{_{64) (l / k 1 3}} )} ...... (11) L i1 ≒ (μ 0 l 1/2) {(l / k 1) - ((l / 64) (l / k 1 3)} ...... (12) as AC resistance R _A1 and internal self-inductance L _i1
Is given. If these are taken as the values of the primary winding of the transformer, the AC resistance R _A2 and the internal self-inductance L _{i2 of the} secondary winding having the radius b and the length l ₂ can be similarly obtained.

Therefore, the self-inductances L ₁ and L ₂ of the primary and secondary windings are the inductances due to the interlinkage of the magnetic flux generated outside each conductor and its current in addition to the obtained internal self-inductances L _i1 and L _i2. And L ₁ = L _i1 + {μ ₀ / (2π)} l ₁ {log (2l ₁ / a) -l} (13) L ₂ = L _i2 + {μ ₀ / (2π)} l ₂ {log (2l ₂ / b) -l} (14)

Next, the improvement of the coupling coefficient due to the skin effect will be described. If the effective lengths of the primary and secondary windings are l _1e and l _2e , the mutual inductance M is l
_{When 1e} ≦ l _2e , M = {μ ₀ / (2π)} l _2e [log {2l _1e / (a + b)}-l] (15) When l _1e > l _2e , M = { μ ₀ / (2π)} l _1e [log {2l _2e / (a + b)}-l] (16). The mutual inductance M of the equations (15) and (16) has the same effect as the second term on the right side of the equations (13) and (14) if the current distribution in the conductor cross section is symmetrical with respect to the origin, that is, the influence of the skin effect. I do not receive it.

Generally, the coupling coefficient k of a transformer is represented by the following equation.

K = M / (L ₁ L ₂ ) ^1/2 (17) A high coupling coefficient is desired to realize a highly efficient transformer. The AC resistance R _A (R _A1 = R _A1 = R _A1 =
FIG. 9 shows theoretical values of frequency characteristics of R _A2 ), self-inductance L (L ₁ = L ₂ ), and coupling coefficient k. It can be seen that when the excitation frequency increases, the AC resistance increases due to the skin effect, but the internal self-inductance decreases, so that a high coupling coefficient can be obtained in the high frequency region.

Next, the film type transformer of the present invention based on the above principle will be described. FIG. 1 is a diagram showing an embodiment of the present invention, showing an example of coil arrangement in the case of forming a transformation ratio of 1: 1 with a circular concentric shaft type. In the figure,
1, 1'is a substrate, 2, 2'is a primary winding pattern, 3, 3
'Is a secondary winding pattern, 2a, 2a' is a primary terminal, 3
Reference characters a and 3a 'are secondary terminals.

In FIG. 1, the primary and secondary winding patterns are formed by arranging two patterns close to each other on a film-shaped thin film insulating substrate 1 by a lithographic technique, an etching technique, a printing technique or the like so as to form a circular concentric axis. Is. For example, as shown in FIG. 1 (a), if two patterns are used as a primary winding and a secondary winding, a film type thin film transformer is formed by this, and a transformer operation is possible even with this one film. is there. However, it is convenient to stack two or more film transformers to improve the low-frequency characteristics and change the transformation ratio.

Now, assuming that the pattern is formed in a circular concentric axis shape starting from the center, the pattern of FIG. 1A is wound clockwise and the pattern of FIG. 1B is wound counterclockwise. It will be. Then, assuming that the pitch and the number of turns are the same, in each of the turns shown in FIG. 1A and FIG. 1B, the winding located outside is always longer than the winding located inside. Therefore, for each turn in FIG. 1 (a), when the winding that is always located outside is the primary winding 2 and the winding that is located inside is the secondary winding 3, in FIG. For each turn, the winding that is always located on the outside is the secondary winding 3 ′, and the winding that is located on the inside is the primary winding 2 ′.
The substrates of (b) are laminated, the terminal 2b is connected to the terminal 2b ', the terminal 3b is connected to the terminal 3b', 2a and 2a 'are primary terminals,
If 3a and 3a 'are used as the secondary terminals, they are shown in FIG.
Magnetic flux is added by the winding pattern of (b), and the lengths of the primary winding and the secondary winding can be made equal. In this way, a plurality of layers, each of which is a laminate of two sheets, are laminated and connected in series or in parallel to each other to form a film type transformer. When connected in series, the resistance value becomes large, and when connected in parallel, the resistance value becomes small. Therefore, the connection is selected so that impedance matching with the load to be connected can be obtained.

FIG. 2 shows an example of coil arrangement in the case of forming a transformation ratio of 1: 1 with a square concentric shaft type, and is the same as the case of FIG. 1 except that the pattern is square. As in the case of FIG. 1, two sheets may be stacked and connected at the central portion to form a unit, and a plurality of sheets may be stacked and connected in series or in parallel.

FIG. 3 shows an example of coil arrangement in the case of constructing an L-shaped concentric shaft type with a transformation ratio of 1: 1.
In the same manner as in the above case, two sheets may be laminated and connected at the central portion to form a unit, and a plurality of sheets may be laminated and connected in series or in parallel. In the case of this embodiment, an electronic circuit or the like can be arranged in a region where the coil is not formed. Of course, L
Not limited to the shape, the pattern may be formed in an arbitrary shape such that there is a region where the coil is not formed in a part of the substrate such as C-shape and E-shape.

FIG. 4 shows an example of coil arrangement for obtaining a transformation ratio of 1: 2 with a circular concentric shaft shape. In FIG. 4A, three windings 10, 11 and 12 are patterned, and the outermost winding 10 is a primary winding and the two inner windings 11 and 12 are secondary. Form the winding. At this time, the central terminal 11b of the secondary winding 11 and the outer terminal 1 of the secondary winding 12
2a is connected so that the currents flowing through the windings 11 and 12 have the same direction, and the length is twice that of the primary winding 10. However, strictly speaking, the length ratio does not become 1: 2 with only one sheet. Therefore, as shown in FIG. 4 (b), the two outer windings 11 'and 12' are secondary windings, and the innermost winding 10 'is a primary winding. The center side terminal 12b 'and the outer side terminal 11a' of the winding 11 'are connected to each other, as in the case of FIG.
(B) is laminated and connected at the central portion. In this way, a transformation ratio of 1: 2 can be obtained. In addition, the windings 11 and 12 and the windings 11 ′ and 12 ′ are connected in parallel and stacked, and then connected in series, and the windings 10 and 10 ′ are stacked and connected in parallel, and It is possible to obtain a ratio of 1: 2. In this embodiment, the transformation ratio is 1: 2, but if the number of primary winding patterns and the number of secondary winding patterns are appropriately changed and they are connected so that the directions of magnetic flux are the same, an arbitrary transformation ratio can be obtained. It is possible to get things.

FIG. 5 shows the transformation ratio-frequency characteristics of the two-layer structure and the four-layer structure for the parallel connection (FIG. 5 (a)) and the series connection (FIG. 5 (b)). Medium 4p,
4s shows 4 layers in parallel and 4 layers in series, respectively. The transformer ratio is for no load. In both series and parallel, the low frequency characteristics are improved by increasing the number of laminated layers. Moreover, because of the no load characteristics, the transformer ratio is 1% in the high frequency region.
It can be seen that the second- and second-order coupling coefficients are equal and nearly 100% coupling is achieved in the high frequency region.

FIG. 6 shows the efficiency-load-frequency characteristics of a four-layer thin film transformer. FIG.
(B) is a case of series connection, and in the figure, 1.4, 21.
Reference numerals 9 and 50.8 represent pure resistance loads (unit: ohm). The efficiency is the ratio of the secondary output to the primary input.

It can be seen that good efficiency is obtained in a high frequency region with a relatively high resistance load, and the skin effect of the winding current becomes more remarkable as the frequency becomes higher, and the efficiency becomes higher.
The peak efficiency at a certain frequency when the load is 50.8 ohms indicates that impedance matching is achieved at this point. In addition, high efficiency of 95% or more is obtained in parallel connection at 1MHz or more and 90% or more in series connection. Therefore, it is said that it is an optimal transformer for switching power supply with higher operating frequency. it can.

In the above embodiment, an example in which no magnetic material is used has been described, but the present invention is not limited to this, and a thin film magnetic material, magnetic powder, etc. are used in combination, and particularly low frequency characteristics are obtained. It goes without saying that improvements may be made.

[0026]

As described above, according to the present invention, since a transformer is formed on a single thin film substrate, it is used for a power source of an electronic device such as a personal computer, a word processor, a mobile phone and the like, which needs to be small and lightweight. It is most suitable as, and it can be expected to be mounted on an artificial satellite. In terms of cost, printing technology, etching technology, and lithographic technology are used to enable inexpensive mass production. In addition, the electrical characteristics are high-frequency characteristics, and the low-frequency characteristics are improved as the number of laminated layers increases, and the low-frequency characteristics are further improved by using thin film magnetic materials and magnetic powders together, and it can be used at commercial frequencies. The thin film power supply and the card power supply can be put into practical use by changing the circuit connection and simultaneously creating other electronic circuits without changing the impedance or providing a plurality of input / output terminals.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a case where a transformation ratio of 1: 1 is configured with a circular concentric shaft shape.

FIG. 2 is a diagram showing an example of coil arrangement in the case of forming a transformation ratio of 1: 1 with a rectangular concentric shaft type.

FIG. 3 is a diagram showing an example of coil arrangement in the case where an L-shaped concentric shaft type and a transformation ratio of 1: 1 are configured.

FIG. 4 is a diagram showing an example of coil arrangement for obtaining a transformation ratio of 1: 2 with a circular concentric shaft shape.

FIG. 5 is a diagram showing a transformation ratio-frequency characteristic when two layers and four layers are formed.

FIG. 6 is a diagram showing efficiency-load-frequency characteristics of a thin film transformer having a four-layer structure.

FIG. 7 is a principle diagram of a conventional transformer.

FIG. 8 is a diagram illustrating a skin effect of a circular cross section.

FIG. 9 is a diagram illustrating a theoretical frequency characteristic value of a coupling coefficient k.

[Explanation of symbols]

1, 1 '... substrate, 2, 2' ... primary winding pattern, 3, 3
'... secondary winding pattern, 2a, 2a' ... primary terminal, 3
a, 3a '... Secondary terminal.

Claims (8)

[Claims] 1. A film type transformer having a primary winding pattern and a secondary winding pattern which are formed close to each other on a thin film substrate. 2. A plurality of film type transformers, each having a primary winding pattern and a secondary winding pattern formed adjacent to each other on a thin film substrate, are laminated to form a primary winding pattern and a secondary winding pattern for each layer.
A film type transformer characterized in that the following winding patterns are connected in series or in parallel. 3. The film type transformer according to claim 1, wherein the primary winding pattern and the secondary winding pattern are concentric. 4. The film type transformer according to claim 3, wherein the pattern formed concentrically has a circular shape or a square shape. 5. The film type transformer according to claim 3, wherein the concentric pattern is formed while avoiding a partial region of the substrate. 6. The film type transformer according to claim 3, wherein the film type transformer has a concentric shaft-shaped pattern wound clockwise from the center to the outside, and a counterclockwise direction from the center to the outside. And a film type transformer having a concentric shaft type pattern wound around each other, and connected in series so that the positional relationship between the primary winding pattern and the secondary winding pattern of each transformer is reversed. Film type transformer. 7. A film type transformer comprising a plurality of film type transformers according to claim 3 as a unit, which are connected in series or in parallel. 8. The film type transformer according to claim 3, wherein the number of the primary winding patterns and the number of the secondary winding patterns formed in the concentric shaft shape are different.