JPH0878253A - Film-type transformer - Google Patents

Abstract

PURPOSE: To obtain an air core film-type transformer which is less affected by an edge effect by a method wherein the film-type transformer is equipped with a primary winding pattern and a secondary winding pattern provided adjacent to each other onto a thin film board, and the windings are made to grow larger in width or thickness with a distance from their center. CONSTITUTION: A right half of a circular board 1 is shown in Figure, wherein a left end indicates the center of the board 1, and a right end shows the right end of the board 1. Winding patterns 2 and 3 are formed on the upside of the board 1, and windings patterns 2' and 3' are formed on the underside by etching or the like. A gap g provided between the windings is set constant, and the widths w1 , w2 ,... of the windings are set so as to grow larger with a distance from their center to satisfy a formula, w1 <w2 <...<wn . By this setup, a film- type transformer of this constitution is less affected by an edge effect caused by a concentration of a magnetic field, prevented from increasing in inner inductance, and improved in degree of coupling between a primary and a second coil.

Description

Detailed Description of the Invention

[0001]

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

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 by using ferrite or amorphous magnetic material for the magnetic core of the inductor and transformer, it is possible to reduce 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 the inductor and the transformer is limited, that is, the product of voltage and time, which is a constraint condition for device design. In order to solve such a problem, the present inventor has already proposed a film type air-core transformer.

The above-mentioned proposal will be briefly described. For example, as shown in FIG. 1, AC resistances R _A (R _{A1 of} two copper conductors having a length of 3 m and a radius of a cross-section circle of 0.2 mm that are very close to each other
= R _A2 ), the self-inductance L (L ₁ = L ₂ ), and the theoretical value of the frequency characteristic with respect to the coupling coefficient k are as shown in FIG. As can be seen from FIG. 2, when the excitation frequency increases, the AC resistance increases due to the skin effect,
Since the internal self-inductance is reduced, a high coupling coefficient is obtained in the high frequency range.

Therefore, as shown in FIG. 3, the primary and secondary winding patterns are formed by bringing two patterns close to the film-like thin film insulating substrate 1 by a lithographic technique, an etching technique, a printing technique, or the like to form a circular concentric shaft. Form. FIG.
As shown in (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 with this single film. It is convenient to stack more than one film transformer to improve low frequency characteristics and change the transformer ratio.

Now, assuming that the pattern is formed in a circular concentric axis shape starting from the center, the pattern of FIG. 3A is wound clockwise and the pattern of FIG. 3B 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 FIGS. 3A and 3B, the winding located outside always has a longer length than the winding located inside. Therefore, for each turn in FIG. 3A, 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, the reverse winding in FIG. For each turn, the winding that is always located on the outer side is the secondary winding 3 ′, and the winding that is located on the inner side 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.

In this film type transformer, good efficiency can be obtained in a high frequency region with a relatively high resistance load, and as the frequency is higher, the skin effect of the winding current becomes more remarkable and high efficiency can be achieved. The winding pattern is not limited to a circular shape, and may be a rectangular concentric shaft shape, an L-shaped concentric shaft shape, or the like, and there may be a region such as a C-shaped or E-shaped substrate where no coil is formed. You may pattern-form in arbitrary shapes. Also, the turns ratio is 1:
The number of primary winding patterns and the number of secondary winding patterns are not limited to 1, and they can be connected so that the directions of the magnetic fluxes are the same, and an arbitrary transformation ratio can be obtained.

[0008]

By the way, in the air-core film type transformer having the structure shown in FIG. 3, when the frequency is increased, the internal inductance is reduced due to the edge effect in which the magnetic field is concentrated on the end winding portion of the transformer. To increase. The inductance L of the conductor is the sum L _in + of the internal inductance L _in caused by the interlinkage of the current and the magnetic flux distributed inside the conductor and the external inductance L _out caused by the magnetic flux outside the conductor.
It consists of L _out . Now, assuming that the self-inductance of the primary coil of the transformer is L ₁ and the self-inductance of the secondary coil is L ₂ , the coupling coefficient k between the primary coil and the secondary coil is k = M / (L ₁ L ₂ ) ^1/2 , as L _in increases and self-inductance increases, the coupling between the primary coil and the secondary coil decreases, and the efficiency decreases.

The present invention has been made in view of the above circumstances, and reduces the influence of the edge effect of the air-core film type transformer utilizing the skin effect of the winding conductor, and reduces the influence between the primary and secondary coils in the high frequency region. The purpose is to prevent a decrease in binding and obtain high efficiency.

[0010]

For this reason, the film type transformer of the present invention is formed on a thin film substrate in close proximity to the film type transformer.
A secondary winding pattern and a secondary winding pattern are provided, and the width or thickness of the winding is increased from the center to the end of each winding. In addition, the present invention includes a primary winding pattern and a secondary winding pattern formed close to each other on the thin film substrate, and the gap between the windings is narrowed from the center of each winding toward the end. Characterize. Further, the present invention is provided with a primary winding pattern and a secondary winding pattern formed close to each other on the thin film substrate, and the width or thickness of the winding is increased from the center of each winding toward the end. With
The feature is that the gap between the windings is narrowed.

[0011]

In the film type transformer of the present invention, the primary and secondary coil patterns of the transformer are formed on the film-like thin film substrate to form the thin film transformer, and the substrate center (coil center) to the substrate end ( The width or thickness of the coil patterns is gradually increased toward the end of the coil, the gap between the coil patterns is gradually reduced, or the width or thickness of the coil patterns is sequentially increased. Together with narrowing the gap sequentially. as a result,
The boundary condition is different between the center and the end, the concentration of the magnetic field at the end is relaxed, the influence of the edge effect is reduced, and the increase of the internal inductance when the frequency is raised is prevented,
High efficiency can be obtained.

[0012]

EXAMPLE FIG. 4 is a diagram for explaining a film type transformer of the present invention. FIG. 4 shows the right half of the circular substrate 1, for example, the left end is the center of the substrate (coil center), the right end is the right end of the substrate (coil end), and the winding pattern 2 is formed on the upper surface of the substrate. 3 is a winding pattern 2 ', 3'on the lower surface of the substrate
Are formed by etching or the like. Figure 4 (a)
The width w of the winding and the gap g between the windings are shown as already proposed. In FIG. 4B, the gap g between the windings is constant, and the width w of the winding becomes w toward the end. ₁ <w ₂ <…… <
1 shows an embodiment of the present invention in which w _n is widened. In the figure, the pattern is flat, but when the pattern is not completely flat, the width here may be called thick.

FIG. 5 shows the frequency-internal inductance relationship for FIGS. 4 (a) and 4 (b).
La corresponds to the transformer in FIG. 4A, and Lb corresponds to FIG.
It corresponds to the transformer of (b). However, FIG. 4 (a)
In Fig. 4, the winding pattern thickness = 0.035 mm, the substrate thickness = 0.05 mm, the gap g = 0.7 mm, the winding pattern width w = 1.7 mm, and in Fig. 4 (b), the winding pattern thickness = 0.03
5 mm, substrate thickness = 0.05 mm, gap g = 0.7
mm, the width of the winding pattern, from the center, 1.7mm, 1.7mm, 1.9mm, 1.9mm,
2.1 mm, 2.1 mm, 2.3 mm, 2.3 mm,
2.5mm, 2.5mm, 2.7mm, 2.7mm,
2.9 mm, 2.9 mm, 3.1 mm, 3.1 mm,
It is 3.3 mm. As can be seen from the figure, when the winding width and the gap between the windings are constant, the internal inductance La decreases from around 100 kHz and increases in the vicinity of 1 MHz, and the coupling between the primary coil and the secondary coil increases. It's getting worse. On the other hand, when the gap between the windings is fixed and the width of the winding is widened toward the end, the internal inductance Lb monotonically decreases, and the coupling between the primary coil and the secondary coil is improved. I know that

FIG. 6 shows an embodiment in which the gap between the windings is widened from the center to the ends as g ₁ <g ₂ <... <g _n, and the width w of the winding is constant. . Also in the case of the present embodiment, the internal inductance L is the same as in the case of FIG.
b decreases monotonically with respect to the frequency, and the coupling between the primary coil and the secondary coil can be improved.

FIG. 7 is a circuit diagram of the transformer of FIG.
z shows the magnetic field distribution when the secondary side is opened, and FIG.
4A corresponds to FIG. 4A, and FIG. 7B corresponds to FIG. 4B. The upper concentration map shows that the magnetic field is stronger toward the right. Comparing the vicinity of the substrate edge, the magnetic field is concentrated in all cases, but it can be seen in FIG. 7A that the circle of the concentrated magnetic field is large and the concentrated magnetic field is strong. It is considered that this strong concentrated magnetic field increased the internal inductance near 1 MHz. On the other hand, FIG.
In (b), it is considered that the concentrated magnetic field is weakened because the boundary conditions of the central portion and the substrate end portion are different, and therefore the internal inductance does not increase.

[0016]

As described above, according to the present invention, in the air-core film type transformer in which the frequency is increased and the coupling between the primary and secondary coils is improved by the skin effect, the influence of the edge effect due to the magnetic field concentration is reduced. It is possible to improve the coupling between the primary and secondary coils by reducing the internal inductance and preventing the increase of the internal inductance.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a skin effect of a circular cross section.

FIG. 2 is a diagram illustrating a theoretical frequency characteristic value of a coupling coefficient k.

FIG. 3 is a diagram illustrating a circular film type transformer.

FIG. 4 is a diagram illustrating a film type transformer of the present invention.

FIG. 5 is a diagram showing a relationship between frequency and internal inductance.

FIG. 6 is a view showing another embodiment of the film type transformer of the present invention.

FIG. 7 is a diagram illustrating an edge effect.

[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 (3)

[Claims] 1. A primary winding pattern and a secondary winding pattern which are formed close to each other on a thin film substrate, and the width or thickness of the winding is increased from the center to the end of each winding. A film-type transformer characterized by. 2. A primary winding pattern and a secondary winding pattern formed close to each other on a thin film substrate, wherein the gap between the windings is narrowed from the center of each winding toward the end. A film type transformer. 3. A primary winding pattern and a secondary winding pattern which are formed close to each other on a thin film substrate, and the width or thickness of the winding is increased from the center to the end of each winding. , A film type transformer characterized by narrowing the gap between windings.