GB2086664A - Small-size transformer - Google Patents

Abstract

A small-size transformer comprises an insulative bobbin 1 having a pair of flanges 7, 14 and a hollow center portion on which an insulated tape wire is wound in layers. The center portion of the bobbin is stepped at 3 to a lower level 14 for accommodating a lead wire so that the tape wire is wound in parallel layers throughout between its innermost and outermost layers. A pair of insulative side members 18 each having U-shaped cross section are fitted to the flanges of the bobbin in positions adjacent to the outermost layer of the winding. A core structure 15, 16 has its outer limbs 15a, 15b accommodated in the slots 31 of the side members and its inner or center limb accommodated inside of the hollow center portion of the bobbin. A base 2 is detachably connected to the bobbin. This base is formed with a plurality of vertical slots 10 for firmly securing tubular lead wires therein to serve as terminal pins for connection to an associated circuit. The bobbin flanges have out-standing members 4a and 8 to accommodate the yokes of the core. <IMAGE>

Description

SPECIFICATION Small-size transformer The present invention relates to a small-size transformer the winding of which comprises an insulated tape wire formed by a plastic film and a tape conductor such as copper or aluminum foil secured thereto or positioned thereon.

It is a conventional practice to use the tape wire for a small-size transformer for use in a device such as DC-DC converters or the like.

The prior art small-size transformer is provided with a bobbin integrally formed with a base.

Furthermore, in accordance with the prior art, tubular lead wire secured to and extending from the tape wire are connected to terminal pins provided on the base for connection to an external circuit. As a result, this integral structure presents difficulty in automatically assembling the transformer elements since the base constitutes an obstacle to straight alignment of the lead wires to the terminal pins, with the result of cumbersome manual shaping of lead wires. Furthermore, since the tubular wires each has a considerable diameter, it is very difficult to wrap them around the terminal pins through usual wrapping techniques. Therefore, the tubular lead wires must reliably be attached to the terminal pins by not using wrapping techniques, thus requiring a special tool and adding complexity to the production process.

The insulated tape wire is wound in layers on the center portion of an insulative bobbin to form a coil, and tubular lead wires are electrically connected to the coiled tape wire.

Therefore, the portion of the tape wire above the underlying tubular wire tends to bulge outwardly. This causes the tape conductor to displace from the center line of the insulative plastic film, so that the safety margin between the edges of the conductor and the insulative film is rendered small. This safety margin tends to decrease as a function of distance away from the bobbin to such an extent that the transformer might fail to meet the rated insulation requirement. Therefore, the prior art has encountered difficulties in properly winding the tape wire in parallel layers to avoid such problems.

On the other hand, in accordance with the prior art, the outer surface of the coiled tape wire is wrapped around by an insulating tape so that the coil is insulated from the core structure. However, since the coiled tape wire partially bulges out due to the lead wire, an air gap is liable to be created between a flange portion of the bobbin and an edge of the wrapped insulating tape, thus resulting in a possibility of a decrease in distance between tape conductor of the tape wire and the core and hence a decrease in insulation. Therefore, difficulties have been encountered in safety standard requirements when subjected to high voltage.

Accordingly an object of the invention is to provide a small-size transformer which allows the insulated tape wire to be wound easily on the bobbin to permit automatic assemblage of transformer elements.

Another object of the invention is to provide a small-size transformer which eliminates the need for providing terminal pins for connection of the lead wires.

A further object of the invention is to provide a small-size transformer which prevents the flat conductor of the winding from being displaced from the correct position due to connection to tubular lead wires.

A still further object of the invention is to provide a small-size transformer which assures excellent insulation.

In order to achieve one or more of these objects the present invention contemplates to separate the bobbin from the base which are detachably engaged during assemblage. The base is provided with a plurality of vertical slots in which the tubular lead wires are inserted and held in position to serve as terminal pins. The center portion of the bobbin is stepped in a direction parallel to the longitudinal axis of the bobbin to permit the tubular lead wire, which is connected to the innermost layer of the tape wire, to be accommodated in the stepped portion so that the tape wire is wound in parallel layers throughout between the innermost layer and the outermost layer.

These and other objects, advantages and the features of the present invention will become apparent from the following detailed description which is given by way of example with reference to the drawings wherein: Figure 1 is an exploded, perspective view of the small-size transformer of the present invention; Figure 2 is a cross-sectional view taken along the lines A-A of Fig. 1; Figure 3 is a side view of the transformer when assembled; and Figure 4 is a view illustrating a tubular lead wire being firmly secured in a vertical slot of the base of Fig. 1.

Referring now to Figs. 1 and 2 a small-size transformer of the invention is illustrated. As illustrated in Fig. 1, the transformer generally comprises an insulative bobbin 1, an insulative base 2 having an elongated opening 1 7 in which the lower portion 4 of the bobbin 1 is detachably engaged when they are assembled together, a pair of insulative covering members or side members 1 8 which are to be fitted to opposite sides of the bobbin 1 in a manner as will be described, and a core structure formed by an E-shaped core 1 5 and a bar core 16.

The bobbin 1 comprises a hollow center portion 6 of a rectangular cross-section around which an insulative tape wire is coiled.

The center hollow structure 6 is stepped partially or entirely of its circumference as shown at 3 by an amount preferably equal to the diameter of a tubular lead wire forming a stepped portion 14 and extends between upper and lower flanges 7 and 20. The lower flanges 20 form part of the lower portion 4 which comprises a pair of elongated plates 4a each having detent lugs or stoppers 5 of a triangular cross-section. The elongated plates 4a and lower flanges 20 are formed by bevelling the corner portions of a rectangular structure so that the outer edges 20a of flanges 20 are offset inwardly from the outer edges of the plates 4a. The upper flange 7 is of a rectangular shape and formed with a pair of upstanding members or guides 8 which extend over the length of the flange 7 between edges 7a which are vertically aligned with the edges 20a of lower flanges 20.

Each of the covering members 1 8 has a generally U-shaped cross-section and a pair of angled end portions. The angled end portions form horizontal slots 32a and 32b, and side plates 1 9 of each covering member 1 8 forming therebetween a vertical slot 31. The upper and lower limb portions of each covering member 1 8 are spaced apart a distance equal to the distance between the upper surface of flange 7 and the lower surface of flange 20.

The base 2 is formed with a plurality of vertical slots 10 on opposite sides thereof, each slot having one or more lugs 21 for holding a tubular lead wire in position to serve as a terminal in a manner as will be detailed later. The base 2 is further formed with a plurality of recesses 9 with which the lugs 5 of the bobbin 1 are engaged when both members are fitted together.

An insulated tape wire is wound on the center portion 6 of the bobbin 1 to form a primary winding 11 and subsequently a secondary winding 1 2 thereon (see Fig. 2). The width of the insulative film of this tape wire is substantially equal to the spacing between the flanges 7 and 20 of the bobbin 1. A tubular lead wire 1 3 is soldered to one end of the tape conductor of the primary winding 11.

Because of the stepped portion-14, the tubular lead wire 1 3 is accommodated therein to allow the overlying layers of the winding to lie in parallel form throughout the circumference of the center portion 6. Although not shown in Fig. 2, to the other end of the primary winding 11 and also to the both ends of the secondary winding 1 2 are soldered other tubular lead wires respectively so that each lead wire is positioned over the stepped portion 14 while not overlying the underlying lead wires.

The disadvantages of the prior art transformer are thus eliminated. DUe to the separation of the base 2 from the bobbin 1. the tape wire can be wound with e3se arollrl(i the bobbin 1.

and then the bobbin 1 i en(Ji!Je(i with the base 2.

When the primary and secondary windings are wound on the bobbin 1, the side covering members 1 8 are fitted to the bobbin so that their upper slots 32a form part of the space in which the bar core 1 6 is accommodated and their lower slots 32b form part of the space in which the lower portion 1 spa of the E-shaped core 1 5 is accommodated. The vertical slots 31 of the covering members 1 8 are positioned to define respective spaces for accommodating the side limbs or portions 1 sub of the core 15.

The E-shaped core 1 5 can be assembled with the bobbin 1 by inserting the side limbs 1 sub of the core into the slots 31 of the insulative side covering members 1 8 and its center limb 1 sic into the hollow center portion 6 of the bobbin 1. A pair of identical magnetic circuits is thus formed by inserting the bar core 1 6 into the space defined by the upstanding member 8 and firmly engaging it into the aligned slots 32a of the side members 1 8 to make contact with the end of each limb of the E-shaped core 1 5. The bare core 1 6 and the E-shaped core 15 are secured to with each other by using suitable holding means such as metal bands or adhesive.

Therefore, the creeping distance between the flat conductor of the coil and the core structure is entirely rendered significantly longer than is possible with the prior art transformer. This arrangement meets the safety standards, or insulation requirements, of the transformer for use in a variety of applications.

The bobbin 1, now fitted with the core structure, is assembled with the base 2 by simply inserting the lower part 4 of the former into the opening 1 7 of the latter until the lugs 5 come into engagement with the recesses 9.

Under this condition, the flange 20 of the bobbin 1 is located above the upper surface 22 of the base 2 as shown in Fig. 3 to leave a space therebetween for the purpose of allowing the tubular lead wires 1 3 to extend to the vertical slots 10 in which each lead wire is firmly secured between the lugs 21 as shown in Fig. 4. This arrangement serves to eliminate the need to provide terminals for electrical connection to an associated device.

The embodiment shown and described above is only a preferred form of the invention. Various modifications and alterations are apparent to those skilled in the art without departing from the scope of the invention which is only limited to the appended claims.

For example, the center portion of the bobbin could be modified so that it has an annular cross-section. In the preferred embodiment shown, the center portion 6 is stepped generally at a right angle, but not necessarily-lim- ited to such angle. Furthermore, the flange 7 can be changed to have a circular configuration with the cross section of the slot 31 being accordingly modified. Still furthermore, the elongated plates 4a can be modified to have stops or projections in the upper portions thereof. The stops or projections get into contact with the upper surfaces 22 when the bobbin 1 fits with the base 2, thus preventing further insertion of the bobbin 1 into the base 2.

Claims (8)

1. A small-size transformer comprising an insulative bobbin having a pair of flanges and a center portion around which an insulated tape wire is wound in layers, at least a part of said center portion being stepped in a direction parallel to the longitudinal axis of said bobbin to accommodate, in the stepped portion, a lead wire connected to the innermost layer of said tape wire.

2. A small-size transformer comprising an insulative bobbin having a hollow center portion around which an insulted tape wire is wound in parallel layers and a pair of flanges between which extends said center portion, two insulative side members, each of which has a U-shaped cross section and a pair of angled end portions, being oppositely positioned in a manner to hold said pair iof flanges between the angled end portions, a E-shaped core structure having an inner part extending into said hollow center portion and two outer parts extending into the U-shaped portions of said insulative side members, respectively, and a bar core positioned in said angled end portions so as to form closed magnetic loops together with said E-shaped core structure.

3. A small-size transformer comprising a core structure having innder, a pair of outer, lower and upper parts, an insulative bobbin having a hollow center portion into which the inner part of said core structure extends and around which an insulated tape wire is wound and a pair of flanges between which extends said center portion, one of said flanges being provided with a pair of first opposed members forming an open-ended slot therebetween to accommodate the upper part of said core structure, the other flange being provided with a pair of second opposed members forming an open-ended slot therebetween to accommodate the lower part and a portion of each of the outer parts of said core structure, and a base detachably engaged with said second opposed member of the bobbin.

4. A small-size transformer as claimed in claim 3, wherein said base is formed with a plurality of elongated slots each including at least one projection for securing therein a portion of a lead wire which is connected to said tape wire to serve as a terminal pin.

5. A small-size transformer as claimed in claim 3, wherein the center portion of said bobbin is stepped in a direction parallel to the longitudinal axis of said bobbin to accommodate, in the stepped portion, a lead wire connected to the innermost layer of said tape wire.

6. A small-size transformer comprising a core structure having inner, a pair of outer, lower and upper parts, an insulative bobbin having a hollow center portion into which the inner part of said core structure extends and around which an insulated tape wire is wound and a pair of flanges between which extends said center portion, one of said flanges being provided with a pair of first opposed members forming an open-ended slot therebetween to accommodate the upper part of said core structure, the other flange being provided with a pair of second opposed members hav ing first engaging means and forming an open-ended slot therebetween to accommo date the lower part of said core structure, a base having second engaging means with which said second opposed members of the bobbin are detachably fitted through said first engaging means, and two insulative side members, each of which has a U-shaped cross section and a pair of angled end portions, being oppositely positioned in a manner to hold said pair of flanges between the angled portions, the outer parts of said core structure extending into the U-shaped portions of said insulative side members respectively.

7. A small-size transformer comprising a core structure having inner, a pair of outer, lower and upper parts, a bobbin having a hollow center portion into which the inner part of said core structure extends and around which an insulated tape wire is wound and a pair of flanges between which extends said center portion, the center portion being stepped in a direction parallel to the longitudi nal axis of said bobbin to accommodate, in the stepped portion, a lead wire connected to the innermost layer of said tape wire, one of said flanges being provided with a pair of first opposed members forming an open-ended slot therebetween to accommodate the upper part of said core structure, the other flange being provided with a pair of second opposed mem bers having first engaging means and forming an open-ended slot therebetween to accom modate the lower part of said core structure, a base having second engaging means with which said second opposed members of the bobbin are detachably fitted through said first engaging means, and two insulative side members, each of which has a U-shaped cross section and a pair of angled end portions, being oppositely positioned in a manner to hold said pair of flanges between the angled end portions, said outer parts of the core structure extending into the U-shaped portions of said insulative side member respectively, said base being formed with a plurality of elongated slots each including at least one projection for securing therein a portion of a lead wire which is connected to said tape wire to serve as a terminal pin for connection to an external circuit.

8. A transformer constructed and arranged substantially as herein before described with reference to and as illustrated in the accompanying drawings.