GB2211669A

GB2211669A - A compact transformer core

Info

Publication number: GB2211669A
Application number: GB8725023A
Authority: GB
Inventors: Seiichi Kijima
Original assignee: Kijima Co Ltd
Current assignee: Kijima Co Ltd
Priority date: 1986-05-09
Filing date: 1987-10-26
Publication date: 1989-07-05
Anticipated expiration: 2007-10-26
Also published as: JPS62262409A; GB2211669B; JPH088172B2; GB8725023D0

Abstract

Identical cores 6, 7 for a compact transformer are made of ferrite material. Each includes a central leg 6b, left and right legs 6c, 6d and a yoke portion 6a integrally formed therewith. The central leg has a trapezoidal cross-section having top and bottom sides extending parallel to the long side of the yoke portion. Each of the left and right legs presents a substantially right-angled triangular cross-section having its hypotenuse extending parallel to and facing the corresponding inclined side of the central leg. The yoke portion is provided with a receiving groove 6e extending longitudinally thereof to receive a bobbin (8). <IMAGE>

Description

"A COMPACT TRANSFORMER CORE".

The present invention relates to a ferrite core for use in a compact transformer employed in various devices such as photographic flash discharge lamps, photographic cameras, TV devices, compact computers, and other general electrical equipments and communication systems.

Compact transformers of various types are already available and one of the most commonly used such transformers is the one utilizing so-called E-E core.

In the accompanying drawings, Fig. 17 illustrates, in a longitudinal section, an example of such a known compact transformer; Fig. 18 is a sectional view taken along a line A-A in Fig. 17; and Fig.

19 is a perspective view of the legs.

E cores 1, 2 are made of sintered ferrite powder in a shape identical to each other and comprise central legs la, 2a, left legs Ib, 2b, and right legs lc, 2c, respectively, so that a closed magnetic circuit may be established by rigidly joining these legs at respective corresponding end surfaces.

As will be apparent from Fig. 19, said E cores 1, 2 respectively include central legs la, 2a each having a rectangular crosssection extending in a direction transverse of the left and right legs and being downwardly offset with respect to the left and right legs so that its bottom is co-planar with the bottom of the associated yoke portion.

The left and right legs lb, 2b, Ic, 2c extend from opposite ends of the associated yoke portions and correspond, in their widths and thicknesses, to the yoke portions.

The central legs la, 2a of said E cores 1, 2 are inserted into a central rectangular opening of a bobbin 4 around which a coil 3 is wound while the left and right legs lb, 2b, lc, 2c extend outside the coil and rigidly joined to each other at their corresponding end surfaces.

The coil 3 is pre-wound around the bobbin 4 and opposite coil ends are affixed to terminal pins 5 positioned in the bobbin 4.

It is an object of the present invention to further reduce the size of the known compact transformers without reducing the efficiency thereof.

The known compact transformer referred to above by way of example has already been manufactured with a configuration dimensioned to be 6 to 7mm long and wide and approximately 5mm high. Although a demand for a flat and compact transformer has been met to some extent by the known compact transformers a still further compact configuration thereof is in demand.

However, it is very difficult to maintain the efficiency at a predetermined or higher level when one tries to miniaturize further the existing compact transformer and such attempts may often cause the cores to be damaged during production as well as a possible break in the coil during the process of winding.

It may further be considered possible to achieve the desired miniaturization by reducing the dimensions of the E cores 1 and 2.

However, in view of the fact that the left and right legs of the respective cores may be as thin as 0.8mm, further reduction of such thickness may cause the core to become damaged during the course of production, particularly during assembly of the transformer and thus make it difficult to achieve a predetermined efficiency due to a shortage of iron.

The present invention has been developed to overcome the problems referred to - above. In its broadest aspect there is provided a compact transformer core each including: a central leg; left and right legs; and a yoke portion all of which are integrally formed of ferrite material; the yoke portion being in the form of a rectangular plate; said central leg having a trapezoidal cross-section defined by top and bottom sides extending in parallel to a long side of the yoke portion and a pair of lateral inclined sides connecting said top and bottom sides, said trapezoidal cross-section having a height smaller than the width of said yoke portion; and each of said left and right legs presenting a substantially right-angled triangular cross-section having a hypotenuse extending in parallel to and facing the associated inclined side of said central leg.

The present invention will now be described in greater detail by way of examples with reference to the remaining figures of the accompanying drawings, wherein: Fig. 1 is a longitudinal sectional view illustrating a first embodiment of a compact transformer utilizing a ferrite core according to the present invention; Fig. 2 is a sectional view taken along a line B-B in Fig. 1; Fig. 3(a) is a side view of said ferrite core as viewed from end surfaces of respective legs; Fig. 3(b) is a sectional view taken along a line C-C in Fig.

3(a); Fig. 4(a) is a front view of a bobbin used in said compact transformer; Fig. 4(b) is a side view of said bobbin; Fig. 5 is a side view similar to Fig. 3(a) illustrating a modified form of the ferrite core; Fig. 6 is a longitudinal sectional view illustrating said compact transformer as incorporated with an upper cover-plate and a lower coverplate; Fig. 7 is a sectional view taken along a line D-D in Fig. 6; Fig. 8(a) is a front view of the upper cover-plate; Fig. 8(b) is a side view of said upper cover-plate; Fig. 9 is a longitudinal sectional view illustrating a second embodiment of a compact transformer utilizing a ferrite core according to the present invention; Fig. 10 is a sectional view taken along a line E-E in Fig. 9;; Fig. ll(a) is a side view of the ferrite core according to the second embodiment as viewed from end surfaces of respective legs; Fig. ll(b) is a sectional view taken along a line F-F in Fig.

11(a); Fig. 12(a) is a front view of the bobbin used in the compact transformer of Fig. 9; Fig. 12(b) is a side view of said bobbin; Fig. 13 is a longitudinal sectional view illustrating a third embodiment of a compact transformer utilizing a ferrite core according to the present invention; Fig. 14 is a sectional view taken along a line G-G in Fig. 13; Fig. 15(a) is a side view of the ferrite core used in the third embodiment as viewed from end surfaces of respective legs; Fig. 15(b) is a sectional view taken along a line K-K in Fig.

15(a); Fig. 16(a) is a side view similar to Fig. 15(a) illustrating a ferrite core used in a fourth embodiment of the present invention; and Fig. 16(b) is a sectional view taken along a line M-M in Fig.

16(a).

Referring to the drawings, the compact transformers of the present invention include cores 6, 7 made of ferrite material in a shape identical to each other such shape being readily apparent from Fig. 3. It should be noted that Fig. 3(a) is a side view of the core 6 as viewed from an end surface of the leg and Fig. 3(b) is a sectional view taken along a line C-C in Fig. 3(a). Although both Figs. 3(a) and 3(b) illustrate only the core 6, the core 7 is in a mirror-image of the core 6, so no further explanation is given so as to avoid any repetition. Likewise similar portions of these cores 6, 7 are designated with the same reference letters.

The core 6 integrally comprises a rectangular plate-like yoke portion 6a, a central leg 6b extending from this yoke portion 6a approximately at its middle area, and a left leg 6c and a right leg 6d extending from opposite ends of the yoke portion 6a in parallel to the central leg 6b.

The central leg 6b is shaped to present a trapezoidal crosssection having top and bottom sides extending in parallel to the long side of the yoke portion 6a. The thickness of this central leg 6b is so selected that the coil surrounding the central leg will never protrude beyond the top and bottom planes (corresponding to the long side) of the yoke portion 6a.

Each of the left and right legs 6c, 6d presents a substantially right-angled triangular cross-section having its hypotenuse extending in parallel to and facing the corresponding inclined side of the central leg 6b. Although this right-angled triangle is shown as having its vertical angle area horizontally cut off, the respective legs 6c, 6d may be shaped so as to present perfect right-angled triangular cross-sections, respectively.

The yoke portion 6a is provided in its inner surface underlying a base of the central leg 6b with a receiving groove 6e extending longitudinally of the yoke portion, into which a corresponding portion of a bobbin is received.

Referring now to Figs. 1 and 2, the compact transformer includes a bobbin 8, a coil 9 wound around the bobbin 8, terminal pins 10 to which opposite ends of the coil 9 are affixed and an insulator tape 11 wound around the coil 9.

As shown in Fig. 4, the bobbin 8 comprises a square-cylindrical winding core 8a and flanges 8b, Sc provided on opposite ends of said winding core 8a, all of which are integrally formed of synthetic resin material. The respective flanges 8b, Sc include at their outer lower zones trapezoidal thickened portions 8d, 8e, formed integrally therewith in which the terminal pins 10 are positioned, and these trapezoidal thickened portions 8d, 8e include, in turn, at their lower ends outwardly directed flanges 8f, 8g also formed integrally therewith.

In the compact transformer as described above, after the coil 9 has previously been wound around the bobbin 8, the central legs 6b, 7b of the respective cores 6, 7 are inserted into the interior of the winding core 8a of the bobbin 8 so as to be opposed to each other, and then the respective legs are rigidly joined at their corresponding end surfaces.

Such securing is achieved by use of adhesive. An arrangement is also possible in which the central legs 6b, 7b are dimensioned to be slightly shorter than the left and right legs so that there is defined a gap between front end surfaces of the respective central legs 6b, 7b after the respective cores 6, 7 have been assembled.

Once the cores 6, 7 have been assembled to each other in this manner, the trapezoidal thickened portions 8d, 8e of the bobbin 8 are received into the receiving grooves 6e, 7e of said cores 6, 7, respectively, so that a relatively wide winding space is available between the flanges 8b, Sc of the bobbin 8. In addition, the yoke portions 6a, 7a of the respective cores 6, 7 rest at their lower end surfaces on top surfaces of the respective flanges 8f, 8g so that an electric insulation is established by said flanges 8f, 8g between the respective terminal pins 10 (or anchoring portion for the opposite ends of the coil) and the respective cores 6, 7.

In this embodiment, the width of each yoke portion 6a, 7a is relatively large and each central leg 6b, 7b is located substantially at a middle level thereof. Such configuration allows the respective yoke portions 6a, 7a to be relatively thin. Additionally, the dimensional feature that the left and right legs 6c, 7c, 6d, 7d correspond in their widths to the respective yoke portions 6a, 7a allows these elements to have sufficient cross-sections to reduce both the length L1 and the width W1 of the compact transformer further than in the conventionally known compact transformers. So far as the height H1 is concerned, the present embodiment is similar to the known compact transformers.However, the inclined sides of the trapezoidal cross-section defined by each central leg 6b, 7b and the hypotenuses of the right-angled triangular cross-section defined by each of the left and right legs 6c, 7c, 6d, 7d may be inclined at angles larger than in the known constructions of compact transformers in order to achieve a flatter configuration.

The compact transformer core 6, 7 in accordance with this embodiment is advantageous particularly in that the left and right legs 6c, 7c, 6d, 7d have sufficiently high mechanical strength to prevent it being damaged, because each of these legs presents the substantially right-angled triangular cross-section and accordingly has an adequate thickness at its base.

A modified form of the ferrite core is shown in Fig. 5. In this modified form it will be noted that each core 12 includes left and right legs 12c, 12d having concave surfaces 12f, 12g, respectively, along their inner sides at upper portions thereof. Except for this feature, the form of the core is similar to the core 6, 7 of the first embodiment and like parts are designated with the same reference letters.

In this way, the core 12 allows the cross-section of each leg 12c, 12d to be effectively enlarged and the concave surfaces 12f, 12g serve to reinforce the left and right legs against any damage.

The compact transformer utiziling the ferrite core of this invention may include an upper cover-plate 13, as seen from Figs. 6 and 7. This upper cover-plate 13 comprises a rectangular plate as shown in Figs. 8(a) and 8(b), which is adapted to be secured to the upper surface of the core 6, 7 by means of adhesive. When the upper cover-plate 13 is made of magnetic material, it is possible to ensure that the troublesome effects in the magnetic path due to unwanted induction caused by an external circuit are reduced to a minimum. The upper cover-plate 13 may be of non-magnetic material and in this case the upper plate 13 effectively protects the coil 3. The upper cover-plate 13 may be also used as a nameplate to display a tradename, or a name of a manufacturer.

A lower cover-plate 14 similar to the upper cover-plate 13 may be provided to further ensure that the troublesome effects in the magnetic path are reduced to a minimum and also to protect the coil.

Referring now to the second embodiment of the compact transformer, which is illustrated in Figs. 9 to 12, the transformer includes: cores 15, 16 which are made of ferrite material shaped identically to each other; a bobbin 17; a coil 18; terminal pins 19; and insulator tape 20. All these components are assembled together in the same manner as in the compact transformer according to the first embodiment.

The core 15 differs from the previously described core 6, 7 in that, as can be seen from Figs. ll(a), ll(b), a receiving groove 15e formed in a lower portion of a yoke portion 15a extends through from the interior to the exterior. This is also true for the core 16. The bobbin 17 is shown in greater detail in Figs. 12(a), 12(b). Trapezoidal thickened portions 17d, 17e of the bobbin 17 are received in the associated cores 15, 16 respectively, so as to provide an enlarged winding space defined between the flanges of the bobbin. Except for this feature, the second embodiment is similar to the first embodiment so that both the concave surfaces 12f, 12g of the left and right legs as shown in Fig. 5 and the upper and lower cover-plates 13, 14 as shown in Figs. 6 to 8 may also be incorporated into this second embodiment.

Referring now to the third embodiment of the compact transformer which is illustrated in Figs. 13 to 15, the transformer includes cores 21, 22. Each core 21, 22 comprises the left and right legs 6c, 6d of the core 6 as shown by Fig. 3 and the upper cover-plate 13 formed integrally with these legs.

Specifically, the core 21 comprises, as can be seen from Fig.

15, left and right legs 21c, 21d, an upper cover-plate 21f formed integrally with the left and right legs, a yoke portion 21a, these elements together defining a box-like surrounding core, and a central leg 21b projecting from the yoke portion 21a within the surrounding core.

The core 22 is of the identical configuration to the core 21.

Fig. 16 illustrates the fourth embodiment of the compact transformer, in which a ferrite core 23 comprises the core 15 as shown by Fig. 11, the upper cover-plate 13 formed integrally therewith, herein referred to as an upper cover portion 23f, left and right legs 23c, 23d, a yoke portion 23a, these elements together defining a box-like surrounding core, and a central leg 23b projecting from the yoke portion 23a within the box-like surrounding core. The yoke portion 23a is provided in its lower portion with a receiving groove 23e extending through from the interior to the exterior.

As has previously been described above with reference to the various embodiments, the compact transformer core comprises the rectangular yoke portion, the central leg being trapezoidal in its crosssection projecting from said yoke portion substantially at the middle area of its length, and the left and right legs having their inner surfaces extending in parallel to the corresponding inclined surfaces of the central leg so that each of said left and right legs is substantially triangular in its cross-section. This configuration allows the left and right legs to have an improved mechanical strength so that damage to the core which might otherwise occur in the course of manufacture and during assembly of the transformer can be effectively avoided. Additionally, such configuration allows the cross-sectional areas of the left and right legs to be effectively enlarged and the length of the core to be correspondingly reduced, resulting in a further miniaturized configuration of the transformer with respect to the known types of compact transformers.

Claims

CLAIMS.

1. A compact transformer core including: a central leg; left and right legs; and a yoke portion integrally formed together from ferrite material; the yoke portion being in the form of a rectangular plate; said central leg having a trapezoidal cross-section defined by top and bottom sides extending in parallel to a long side of the yoke portion and a pair of lateral inclined sides connecting said top and bottom sides, said trapezoidal cross-section having a height smaller than the width of said yoke portion; and each of said left and right legs presenting a substantially right-angled triangular cross-section having a hypotenuse extending in parallel to and facing the associated inclined side of said central leg.

2. A compact transformer core according to claim 1, wherein said yoke portion is provided in its portion underlying a base of said central leg with a receiving groove into which a corresponding portion of a bobbin is received.

3. A compact transformer core according to claim 1 or 2, wherein a cover-plate made of magnetic or non-magnetic material is secured to surfaces of the left and right legs corresponding to bases of the respective right-angled triangular cross-sections defined by said left and right legs, respectively, so as to close a gap otherwise defined between the left and right legs.

4. A compact transformer core according to claim 1 or 2, wherein a cover-plate made of magnetic material is provided integrally with the left and right legs on surfaces of said left and right legs corresponding to bases of the respective right-angled triangular crosssections defined by said left and right legs, respectively, so that the yoke portion, the left and right legs and the cover-plate form together an integral box-like surrounding core within which the central leg projects from the yoke portion.

5. A compact transformer wherein there are provided a pair of compact transformer cores according to claim 1 or 2, wherein said cores are shaped in a mirror image relationship with each other so that the pair of cores may be assembled with the bobbin having a cylindrical winding core around which the coil has been wound by inserting the central leg of one core into said winding core from one end of said bobbin while the central leg of the other core into said winding core from the other end of said bobbin and then by integrally connecting the pair of cores.

6. A compact transformer core constructed substantially as herein described with reference to and as illustrated in Figs. 1 to 4; Figs. 5 to 8; or Figs. 9 to 12; or Figs. 13 to 15; or Fig. 16 of the accompanying drawings.