EP0450448A1

EP0450448A1 - Flat-type transformer

Info

Publication number: EP0450448A1
Application number: EP91104678A
Authority: EP
Inventors: Tetsuya Yokokawa
Original assignee: Toshiba Lighting and Technology Corp
Current assignee: Toshiba Lighting and Technology Corp
Priority date: 1990-03-29
Filing date: 1991-03-25
Publication date: 1991-10-09
Also published as: JPH03280409A

Abstract

A flat-type transformer comprises a plurality, at least two, of planar coils (12a, 12b, 12c) and a plate-like electric insulator (13) disposed between adjacent two planar coils so as to form a stacked structure of the insulator and the planar coils. This stacked structure are sandwiched between a pair of magnetic members (14a, 14b) disposed on both the sides of the stacked structure with electric insulators (13) being interposed between the magnetic members and outermost planar coils. The planar coils having substantially the same outer diameter in the stacked structure. Each of the planar coils has a spiral structure in a plane.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a flat-type transformer having a thin compact size and light weight suitable for a transformer utilized for a power device, an invertor or an oscillator particularly for improving coefficient of coupling between a plurality of flat-type plane coils of the transformer.
Usually, a transformer is composed of a primary coil and a secondary coil both wound around iron cores. These primary and secondary coils are generally formed of copper wires in form of coil, and accordingly, there is a limit for constructing the transformer having a thin and compact structure and light weight.
Recently, in view of the above point, a planar coil such as sliced coil or inductance element in which a conductor element is printed on a print circuit substrate in a coiled or vortex (spiral) shape.
The sliced coil is usualy formed by first forming a spiral cylindrical member from an electroconductive thin band plate-like member having a predetermined width and then slicing the cylindrical member along the axial direction thereof so as to produce a plurality of sliced coil elements each having a required thickness. Each of the thus formed sliced coil has of course a spiral or vortex shape.
A flat plane-type transformer, called flat transformer hereinlater, utilizing such sliced coils has been provided. The flat transformer comprises a plurality of planar coils stacked with plate-like electric insulators interposed between adjacent planar coils. The stacked structure of the planar coils and the insulators are sandwiched by a pair of magnetic members with the electric insulators also interposed between the magnetic members and the outermost planar coils, thereby to form a flat transformer provided with a pair of magnetic members formed as primary and secondary sides, respectively.
However, in the conventional transformer of the described structure, there has an tendncy to meet the inner diameters of the respective planar coils because the coils are usually formed by winding up them around bobbins, for example. The conventional flat transformer comprises a plurality of planar coils having different outer diameters. Accordingly, the coefficient of coupling between the adjacent planar coils is low and, hence, the coefficient of conversion of the transformer itself is reduced, thus providing a significant problem. It is considered that this adverse phenomenon is caused by the increasing of the the leakage of the magnetic flux into a space formed by the difference in the outer diameter of the respective planar coils.

SUMMARY OF THE INVENTION

An object of the present invention is to substantially eliminate the defects encountered in the prior art and to provide a flat-type transformer having a compact structure capable of increasing the coefficient of coupling between the planar coils and improving the coefficient of conversion of the transformer.
This and other objects can be achieved according to the present invention by providing a flat-type transformer comprising a plurality, at least two, of planar coils, a plate-like electric insulator disposed between adjacent two plane coils so as to form a stacked structure of the insulator and the planar coils, and a pair of magnetic members disposed on both the sides of the stacked structure with electric insulators being interposed between the magnetic members and the outermost planar coils, the planar coils having substantially the same outer diameter in the stacked structure.
It is preferred to form each of the planar coils so as to have a vortex structure in a plane.
According to the structure of the flat-type tansformer of the present invention, since the outer diameters of the planar coils are made substantially equal to each other, the coefficient of the coupling between the respective planar coils can be increased and the coefficient of conversion of the transformer can be also improved.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

Fig. 1 shows a cross section of a flat-type transformer according to the present invention;
Fig. 2 is a plan view of a planar coil having a vortex shape;
Fig. 3 shows a cross section of a flat-type transformer of conventional type; and
Fig. 4 shows the relation between the coefficient of coupling and the outer diameter ratio of the respective planar coils.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In advance of the description of a preferred embodiment of a flat-type transformer according to the present invention, a background art is first described with reference to Figs. 2 to 4 for a better understanding of the present invention.
Fig. 2 shows one example of a planar coil 1 formed by coiling an electroconductive material 2 into a vortex shape in one plane.
Fig. 3 represents a flat transformer 3 constructed by utilizing the planar coil 1 such as shown in Fig. 2 and the flat transformer 3 comprises a plurality, three in the illustration, of planar coils 1a, 1b and 1c stacked with plate-like electric insulators 4 interposed between adjacent two planar coils 1a and 1b, for example. The laminated structure of the planar coils 1 and the insulators 4 are sandwiched by a pair of upper and lower plate-like magnetic members 5a and 5b with the electric insulators 4 also interposed between the magnetic members 5a and 5b and the outermost planar coils 1a and 1c, thereby to form a flat transformer 3 provided with a pair of magnetic members 5a and 5b formed as primary and secondary sides, respectively.
However, as described before, the conventional flat transformer comprises a plurality of planar coils having different outer diameters. Accordingly, the coefficient of coupling between the adjacent two planar coils is low and, hence, the coefficient of conversion of the transformer itself is reduced. It is considered that this adverse phenomenon is caused by the increasing of the the leakage of the magnetic flux into a space formed by the difference in the outer diameter of the respective planar coils.
Fig. 4 shows the relation between the outer diameter ratio of the planar coils 1a to 1c and coefficient of coupling thereof. Referring to Fig. 4, for example, in a case where optional two plane coils utilized have the outer diameter ratio of 1 : 2 (i.e. 50% of the outer diameter difference), the coefficient of coupling is largely reduced in comparison with a case where the planar coils have substantially the same outer diameter (i.e. the outer diameter ratio of 1 : 1).
The present invention conceived in consideration of the above prior art will be described hereunder with reference to Fig. 1.
Referring to Fig. 1, a flat transformer 11 comprises a plurality, three in the illustration for the sake of convenience, of planar coils 12a, 12b and 12c, a plurality of plate-like electric insulators 13 and 13 each interposed between adjacent two planar coils 12a and 12b, for example, so as to form a stacked structure of the planar coils and the insulators, and a pair of upper and lower, as viewed, magnetic members 14a and 14b so as to sandwich the stacked structure therebetween with further insulators 13 interposed between the magnetic members and the outermost planar coils.
The respective planar coils 12a to 12c are formed of the electroconductive material. The magnetic member 14a and 14b are constructed as the primary and secondary sides of the transformer 11.
However, in the present embodiment, the planar coils 12a to 12c are all formed so as to have substantially the same outer diameter. This structure is very significant as understood from the disclosure of Fig. 4. According to this structure, since the outer diameter ratio becomes substantially 1 : 1, (i.e. 100% in the graph) the coefficient of coupling K between the respective planar coils 12a to 12c is remarkably improved, for example, to 0.95% and the coefficient of conversion as the transformer can be also remakably improved.
In a preferred embodiment, it may be desired to make coincident the inner diameters of the respective planar coils 12 with each other.
In the described embodiment, there is proposed a flat-type transformer comprising three planar coils, but the present invention is applicable to a transformer having at least two planar coils.
It is to be understood that the present invention is not limited to the described embodiment and many other changes or modifications may be made without departing from the scope of the appended claim.
For example, in a modification, any other type planar coil may be utilized in place of vortex coil as described hereinabove as far as the coils have flat planar shapes and all have substantially the same outer diameters.

Claims

A flat-type transformer (11) of the type comprising a coil means having a plurality of planar coils (12a, 12b, 12c) a plate-like electric insulator means (13) disposed between adjacent two planar coils so as to form a stacked structure of the insulator means and the planar coils, and a pair of magnetic member (14a,14b) disposed on both the sides of the stacked structure with electric insulators (13) being interposed between the magnetic members (14a, 14b) outermost planar coils (12c or 12a) the transformer being characterized in that said planar coils have substantially the same outer diameter in the stacked structure.
A flat-type transformer according to claim 1, wherein each of said planar coil has a vortex structure in a plane.