JPH08306540A - Planar air-core transformer - Google Patents

Abstract

PURPOSE: To provide a planar air-core transformer high in transformation efficiency by reducing both eddy current loss and continuity loss. CONSTITUTION: A coil pattern 4 is made so that the rate of the area S surrounded by the one turn at the innermost end to the area Z surrounded by the one turn at the outermost end of a vortex may be within the range of not less than 9% and not more than 30%. In the range of not less than 9% in area percentage, coil patterns 4 cease to be formed in the center area of a vortex that magnetic fluxes transmit convergently, and the loss of eddy currents by the transmission of the magnetic fluxes decreases, and besides in the range of not more than 30% in area percentage, the width of the coil pattern 4 can be widened more than the width where the loss of continuity increases, so the continuity loss can be reduced, and a planar air-core transformer high in transformation efficiency can be manufactured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a planar air core transformer formed by laminating substrates having a spiral coil pattern formed on the surface of a substrate with an insulating layer interposed therebetween.

[0002]

2. Description of the Related Art As is well known, a transformer is used in a DC-DC converter incorporated in an inverter or a switching power supply. In recent years, high-frequency circuit driving has been performed from the viewpoint of reducing the size and weight of switching power supplies and the like, and this has led to the use of inverters and DC-DC.
Planar air-core transformers are promising as transformers used in converters and the like.

As shown in FIG. 4, a planar air-core transformer has a spiral coil pattern 4 formed on the surface (on one side) of a substrate 2, and the substrate 2 having the coil pattern 4 formed thereon has an insulating layer (see FIG. (Not shown), the one coil pattern group 4 is connected as a primary coil group, and the other coil pattern group 4 is connected as a secondary coil group. Further, as a planar air-core transformer, unlike FIG. 4, a coil pattern 4 is formed on both front and back surfaces of the substrate 2, and the substrate 2 having the coil pattern 4 formed on both surfaces is laminated via an insulating layer. There are also things.

[0004]

However, the above planar air core transformer has a problem that the transformer efficiency is poor. Therefore, the present applicants searched for the cause of the poor transformer efficiency and found that the transformer efficiency deteriorated due to the following reasons.

As is well known, the magnetic flux is converged and transmitted in the spiral center region of the coil pattern 4. However, in the conventional planar air-core transformer, as shown in FIG. 4, since the coil pattern 4 is formed from the vicinity of the spiral center point, most of the spiral center area where the magnetic flux is focused and transmitted is also present. The coil pattern 4 is formed so as to occupy the area, and the focused magnetic flux passes through the coil pattern 4 to generate a strong eddy current in the coil pattern 4, which deteriorates the transformer efficiency due to the eddy current loss. It was

Therefore, in order to reduce the eddy current loss, the applicant of the present invention determines the area of a portion surrounded by one turn portion at the innermost end of the coil pattern 4 (hereinafter referred to as the innermost turn enclosing area). An extremely wide planar air core transformer was prototyped. However, the transformer efficiency of the prototype planar air-core transformer was also poor. When the cause was investigated, the following conclusions were obtained. That is, normally, the spiral outer diameter as shown in FIG. 4 is predetermined from the viewpoint of downsizing the planar air-core transformer, and the width H of the coil pattern 4 is narrowed in order to increase the innermost turn enclosing area. Therefore, the current-carrying region of the alternating current in the coil pattern 4 is narrowed, the conduction loss is increased (the inductance is increased although it is smaller than the increase of the conduction loss), and the transformer efficiency is deteriorated.

The present invention has been made to solve the above-mentioned problems, and an object thereof is to provide a planar air-core transformer having a reduced eddy current loss and a reduced conduction loss and high transformer efficiency. Is.

[0008]

In order to achieve the above object, the present invention is constructed as follows. That is, the present invention is a planar air-core transformer formed by stacking substrates, each having a spiral coil pattern formed on the surface of a substrate, with an insulating layer interposed therebetween, in the spiral coil pattern formed on the surface of the substrate. The ratio of the area surrounded by the innermost one turn portion to the area surrounded by the outermost one turn portion is set in the range of 9% or more and 30% or less.

[0009]

In the present invention having the above structure, the coil pattern is formed in such a manner that the ratio of the area surrounded by the innermost one turn portion to the area surrounded by the outermost one turn portion of the spiral coil pattern is 9% or more. By forming the coil, almost no coil pattern is formed at the center of the vortex where the magnetic flux is focused and transmitted, generation of strong eddy current in the coil pattern due to transmission of the focused magnetic flux is prevented, and eddy current loss of the coil pattern is reduced. Reduce.

Further, by forming the coil pattern within the range of the area ratio of 30% or less, the coil pattern can be formed with a wider width than the width in which the conduction loss increases, so that the conduction loss is reduced. Therefore, by forming the coil pattern in the area ratio of 9% or more and 30% or less, the eddy current loss is reduced, the conduction loss is also reduced, and the transformer efficiency is improved.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. In the description of the present embodiment, the same reference numerals will be given to the same names as those in the conventional example, and the duplicated description will be omitted.

The present inventor pays attention to the production of a planar air-core transformer having a transformer efficiency such as a DC-DC converter or an inverter having a transformer efficiency standard value P or more, and determines the innermost turn enclosing area of the coil pattern 4. Various types of planar air core transformers were prototyped with various changes and the transformer efficiency was measured. As a result, as shown in FIG. 1, the ratio of the innermost turn enclosing area S to the area (hereinafter referred to as the outermost turn enclosing area) Z surrounded by the outermost one turn portion of the coil pattern 4 (area ratio (area ratio ( (S / Z) ×
It was found that the relationship between 100%)) and the transformer efficiency is as shown by the curve A in FIG.

From this curve A, in order to obtain the transformer efficiency of the standard value P or more of the transformer efficiency, the ratio (area ratio) of the innermost turn enclosing area S to the outermost turn enclosing area Z is 9% or more and 30% or more. It was found that the coil pattern 4 should be formed within the following range.

The curve A showing the relationship between the transformer efficiency and the area ratio can be explained as follows by the curves B and C in FIG. A curve B shows the relationship between the transformer efficiency and the area ratio when only the eddy current loss is taken into consideration. As shown in the same curve B, as the area ratio increases, the coil pattern 4 is not formed in the vortex central region where the magnetic flux is converged and transmitted, so that the generation of the eddy current due to the transmission of the magnetic flux is suppressed, Eddy current loss is reduced and transformer efficiency is improved.

The curve C shows the relationship between the transformer efficiency and the area ratio when only the conduction loss is taken into consideration. As shown by the curve C, as the area ratio becomes smaller, the coil pattern 4 can be formed with a wider width, so that the energization region of the alternating current is expanded and the conduction loss is reduced. The transformer efficiency is improved.

In practice, the eddy current loss and the conduction loss act together, and the area ratio X where the curves B and C intersect.
In the range where the area ratio is smaller than the above, the eddy current loss increases as the area ratio decreases, and therefore the curve A showing the actual transformer efficiency is a curve that decreases as the area ratio decreases as shown in the above curve B. On the contrary, in the range where the area ratio is larger than the area ratio X, the conduction loss increases as the area ratio increases.
A curve A is a curve that follows the curve C and descends as the area ratio increases.

From the above, as described above, by forming the coil pattern 4 in the area ratio of 9 to 30%, the transformer efficiency of the transformer efficiency of the DC-DC converter, the inverter or the like, which is the standard value P or more, can be obtained. Obtainable.

As shown in FIG. 1, when one turn portion of the innermost end and the outermost end of the coil pattern 4 draws a perfect circle, the above area ratio is defined as the ratio of the spiral inner diameter d to the spiral outer diameter D. (Diameter ratio ((d / D) × 100%)), and the area ratio 9 to 30% can be replaced with the diameter ratio 30 to 55%.

In this embodiment, substrates having coil patterns 4 formed in an area ratio of 9 to 30% are laminated with an insulating layer interposed therebetween, and one of the coil pattern 4 groups is a primary coil group. And the other group of coil patterns 4 were connected as a secondary coil group to produce a planar air-core transformer, and high transformer efficiency compatible with a DC-DC converter, an inverter or the like could be obtained.

According to this embodiment, by forming the coil pattern 4 in such a manner that the ratio of the innermost turn enclosing area to the outermost turn enclosing area of the coil pattern 4 is 9% or more and 30% or less, eddy current loss is reduced. It is possible to manufacture a planar air-core transformer having a high transformer efficiency, which can reduce the conduction loss as well as the DC-DC converter, the inverter, and the like.

Further, as described above, if the coil pattern 4 is formed in the area ratio of 9 to 30%, a planar air core transformer having a high transformer efficiency can be manufactured. Therefore, the size standard such as the spiral outer diameter is changed. Even if such a situation occurs, an appropriate area of the innermost turn of the coil pattern 4 can be quickly obtained, and it is possible to deal flexibly.

The present invention is not limited to the above-mentioned embodiments, and various embodiments can be adopted. For example, in the above-described embodiment, as shown in FIG. 1, the coil pattern 4 formed so that one turn portion of the spiral of the coil pattern 4 draws a circle has been described as an example. As shown in the drawing, the present invention can be applied to other spiral-shaped coil patterns 4 such as a coil pattern 4 formed so that one turn of a spiral draws a rectangular shape and a coil pattern 4 formed to draw an ellipse.

The present invention can also be applied to a planar air-core inductor in which the substrates 2 on which the coil patterns 4 are formed are laminated via an insulating layer and the coil patterns 4 are connected in series.

[0024]

According to the present invention, the ratio of the area surrounded by the innermost one turn portion to the area surrounded by the outermost one turn portion of the spiral coil pattern formed on the substrate surface is 9%. By forming the coil pattern in the range of 30% to 30%, the coil pattern is hardly formed in the central region of the spiral where the magnetic flux is focused and transmitted, and the eddy current loss due to the transmission of the magnetic flux is reduced. In addition, since the width of the coil pattern can be made wider than the width in which the conduction loss increases, the conduction loss can be reduced and the DC efficiency of the transformer is high.
It is possible to provide a planar air-core transformer applied to a DC converter, an inverter, or the like.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a coil pattern and its area ratio in this embodiment.

FIG. 2 is a graph showing a relationship between a transformer efficiency and an area ratio in a coil pattern.

FIG. 3 is an explanatory diagram showing an example of another coil pattern.

FIG. 4 is an explanatory diagram showing an example of a conventional coil pattern.

[Explanation of symbols] 2 substrate 4 coil pattern

Claims (1)

[Claims] 1. A planar air-core transformer formed by stacking substrates, each having a spiral coil pattern formed on the surface of a substrate, with an insulating layer interposed therebetween, wherein the spiral coil pattern formed on the surface of the substrate is the maximum. A planar air-core transformer characterized in that the ratio of the area surrounded by the innermost one turn portion to the area surrounded by the outermost one turn portion is set in a range of 9% or more and 30% or less.