WO2000074090A9

WO2000074090A9 - Simplified laminar core transformer and method of manufacturing

Info

Publication number: WO2000074090A9
Application number: PCT/US2000/015409
Authority: WO
Inventors: Russell Lee Machado
Original assignee: Pulse Eng Inc
Priority date: 1999-06-01
Filing date: 2000-06-01
Publication date: 2002-06-20
Also published as: AU5595800A; WO2000074090A1; KR20020033631A; CN1357148A

Abstract

A simplified microelectronic transformer suitable for surface mount applications comprises a central spool (102) upon which the transformer primary (104) and secondary (106) windings are wound. A series of 'E' shaped laminar core elements (108) are fitted within the spool in an alternating, interlocking fashion so as to form a substantially rectangular core assembly. A molded cover (120) is fitted within the central region of the wound bobbin assembly; the cover 'snaps' into the core thereby retaining it in a substantially fixed position with respect to the spool and other transformer components. This arrangement obviates the need for varnish or other coatings to maintain the core elements in place, and improves the thermal and electrical performance of the transformer. A method of fabricating the simplified transformer is also disclosed.

Description

SIMPLIFIED LAMINAR CORE TRANSFORMER AND METHOD OF MANUFACTURING

Background of the Invention Field of the Invention The invention relates generally to miniature electrical devices used in printed circuit board and other microelectronic applications and particularly to an improved microelectronic transformer having a non-varnished laminar core, and a method of fabricating the same. Background

Transformers are devices that increase or decrease the voltage of alternating current. They are usually fabricated by winding several coils of wire around a large magnetic core. One coil, called the primary, is connected to the input circuit, whose voltage is to be changed The other coil, called the secondary is connected to the output circuit, which is where the electricity with the changed (transformed) voltage is used

As the alternating current in the input circuit travels through the primary, it sets up a magnetic field that changes in intensity and direction in response to the alternating current. The changing magnetic flux induces an alternating voltage in the secondary The ratio of the number of turns in each coil determines the transformation ratio.

For example, if there are twice as many turns in the primary as in the secondary, the output voltage will be half that of the input voltage. On the other hand, the output current will be twice as much as the input current.

Cores may be formed of laminated layers of magnetically permeable materials. The layers of laminated cores are typically secured together with an adhesive or varnish and may be covered with an insulating material. The use of an adhesive or varnish an insulating layer can add to production costs and can reduce the thermal characteristics of the transformer

Summary of the Invention

In a first aspect of the invention, an improved and simplified microelectronic transformer is disclosed which utilizes a laminar construction core which is held together by a transformer cover element In one embodiment, the cover element includes generally a top surface and four side walls which engage various portions of "E shaped" laminar transformer core elements so as to maintain the position and alignment thereof The transformer cover element can be fabricated from molded plastic and allow some degree of flexure of the side walls when being positioned on the transformer assembly the cover element can 'snap into the assembly The lower edges of two of the side walls of the cover element are received by the inner edges of the laminar core elements within the opening formed on the interior of the core, while the lower edges of the remaining two side walls are received on the outer edge of the core elements. This arrangement secures the laminar core elements in a fixed relationship in all directions The cover element also includes a series of apertures at its corners to permit airflow over the top of the assembly beneath the cover element. Since no varnish or other thermally insulating coatings are used, the heat transfer properties of the transformer are improved, thereby increasing component longevity and performance In a second aspect of the invention, a method of fabricating the transformer of the present invention is described. In one embodiment of the method, the wound bobbin assembly is formed by winding the primary and secondary windings around a central spool having an aperture formed longitudinally through its center. A series of "E shaped" laminar core pieces are also formed. The laminar core pieces are arranged in overlayed fashion from the two ends of the longitudinal axis of the spool in an alternating, interlocking fashion thereby forming a rectangular or square laminar core element. The molded cover element is then positioned over the central portion of the wound bobbin assembly and "snapped" therein such that the lower edges of two opposing side walls of the cover element are received within the opening formed on the interior of the core. The lower edges of the remaining two opposing side walls are received on the outer edges of the core elements, thereby securing the core elements in place. No varnish or other coatings are required to maintain the position of the core elements with the transformer assembly, thereby reducing the cost of manufacturing the assembly.

Brief Description of the Drawings Fig. 1 is an exploded perspective view of a simplified transformer prior to assembly Fig. 2 is a perspective view of the transformer of Fig. 1 , shown fully assembled Figs. 3a 3c are top, side and front plan views of the cover element of the transformer illustrated in Fig. 1. Figs. 4 is a perspective view of a simplified transformer.

Fig. 5 is a perspective view of a simplified transformer. Fig. 6 is a flow diagram illustrating the method of manufacturing according to the present invention.

Detailed Description of the Invention Reference is now made to the drawings wherein like numerals refer to like parts throughout. As shown in Fig. 1 , the transformer 100 includes a bobbin spool 102 with a plurality of electrical terminals 103, a primary winding 104, a secondary winding 106, a plurality of laminar core elements 108, and a cover element 1 10. The spool 102 is generally of a rectangular cross section, although it will be recognized that other shapes may be used. A substantially rectangular aperture 1 12 is formed within the center portion of the spool 102. The aperture runs longitudinally down the central axis 1 14 of the spool 102. The aperture 1 12 is sized so as to receive the central proiections of the laminar core elements 108, described further below The spool 102 includes two terminal rails 1 1 1 disposed at either end of the spool and offset to one side of the aperture 1 12. Each terminal rail 1 1 1 includes winding lead channels 1 13 formed in its bottom side to accommodate the ends of the wires of the primary and secondary windings 104, 106, as described further below.

The primary and secondary windings 104, 106 can be insulated electrical conductors, and are wound around the spool 102 in such a fashion so as to enhance magnetic coupling between the windings, as is well known in the electrical arts. The ends 121 of the windings 104, 106 are routed through the channels 1 13 of the terminal rails 1 1 1 and coupled to the terminals 103. The terminals 103 are molded within the terminal rails 1 1 1 and adapted for surface mounting or through hole mounting to a circuit board or other components. After winding, the spooled windings may be sealed with an electrically insulating covering (such as a polymer) if desired The core elements 108 are a series of substantially flat, magnetically permeable plates formed in the shape of an "E". The individual core elements 108 are formed from a nickel iron alloy, although it will be appreciated that other magnetically permeable materials and other dimensions may be used. The plates are positioned at either end of the spool 102 and stacked or layered in an alternating fashion. The central projection (post) 116 of each core element 108 is inserted within the rectangular aperture as shown in Figs. 1 and 2. The length of the central projection 116 and lateral projections 1 18a, 1 18b is such that when the transformer core is assembled, all projections 116, 118 at least partially overlap with corresponding ones of the projections from the opposing laminar core elements 108. The core is therefore formed by interleaving opposing ones of the core elements 108 in an alternating fashion. The assembled core (and transformer 100) is illustrated in Fig. 2. Referring to Figs 1 , 2, and 3a 3c, the cover element 1 10 includes a substantially planar top 120 and four walls

122a-122d (two side walls 122a, 122c, and two end walls 122b, 122d) projecting downward from the top 120. Apertures 130a-130d are formed in the corner regions of the cover element as shown. These apertures 130a-130d allow for air to flow under and through the cover element 1 10, thereby enhancing cooling of the transformer coils and core. Additionally, the apertures separate the individual side and end walls 122a 122d, allowing them to flex substantially when the cover 1 10 is installed on the transformer 100, as described in greater detail below. Each side wall is formed so that it is sufficiently pliable and resilient to permit flexing during cover installation. Each of the side and end walls 122a-122d further includes one or more ridges 124a and 124c on its outer surfaces. These ridges cooperate with the inner/outer edges, respectively, of the core elements 108 such that the cover element 110 is retained in position when completely installed on the transformer 100. Specifically, the ridges 124a-124d are oriented horizontally and placed at a vertical position on their respective side or end walls 122a- 122c such that when the cover element 1 10 is completely seated, the ridges catch and retain the lower edges 132a- 132c of the bottom most one of the core elements 108, as shown in Fig. 2. For the two opposing lateral side walls 122a, 122c, the ridges 124a, 124c are on the exterior surface 128a, 128c of the walls 122a, 122c so as to capture and hold the inner bottom edge 132a, 132c of the lowest core element 108. For the two opposing end walls 122b, 122d, they engage the outer bottom edges 132b, 132d of the core element 108. The core elements 108 are therefore biased upwards toward the top surface 120 and against the upper interior surface 140 of the spool aperture 1 12, thereby holding them in a fixed position relative to each other and the spool 102. The two end walls 122b, 122d further include a set of stops or risers 142 which are formed on the interior surfaces 126b, 126d of the end walls; these stops 142 act as positioning guides for the core elements 108, and are positioned on the end walls 122b, 122d with respect to the ridges 124b, 124d so as to securely capture the core elements 108 when assembled and limit their movement in the vertical direction Alternatively, the side walls could also extend beyond the core element and engage the outer edges in the same manner as the end walls

Referring now to Fig. 4, an alternate embodiment of a simplified transformer will be described. As shown in Fig. 4, the transformer 200 utilizes a substantially circular or rounded transformer core 202, terminal rails 21 1 , and cover element 210. The core elements 208 are again stacked and interleaved in an alternating fashion, as was described in connection with Fig. 1. The cover element 210 includes two opposing curved lateral side walls 220a, 220c, and two opposing curved end walls 220b, 220d. The lateral side walls 220a, 220c have ridges (not shown) disposed on their outer surfaces 226a, 226c near the lower edge of the walls. As in the embodiment of Fig. 1, these ridges engage corresponding edges 230a, 230c of the bottom core elements 208, thereby fixing the core elements 208 with respect to the rest of the transformer 200 without the use of varnish or adhesives. Referring now to Fig. 5, a further embodiment of a simplified transformer 300 will be described. In this embodiment, the rectangular core elements 308 are retained by a cover element 310 which fits around the spool 302 and windings. Additionally, the side and end walls of the prior embodiments are replaced by separated pairs of tabs 311a, 311 b, 31 1 c, 311 d which retain the core elements both laterally and longitudinally. Tabs 31 1 a and 311 c are fitted with ridges (not shown) as in the embodiments of Figs. 1 and 4. Tabs 311 b and 31 1 d are fitted with stops (not shown) on the inner surfaces 312a, 312c of the end tabs 31 1 b, 311 d. This embodiment requires a reduced amount of material to fabricate, and allows for increased ventilation of the spool and windings As with the prior embodiments described, the transformer 300 of Fig. 5 requires no varnish or other adhesives to maintain the physical integrity of the core or device as a whole.

It will be recognized that while the foregoing embodiments have been described in detail, other embodiments and modifications may be made. For example, the transformer 100 as a whole and core elements 108 may be formed in shapes other than the rectangle or substantially circular shapes set forth in Figs. 1 and 4, respectively, to include square, elliptical, or polygonal shapes. Additionally, the shape, location, and material composition of the cover element 104

(including its ridges 124 and stops 142) may be altered as desired. All such modifications and alternate embodiments are considered to be within the scope of the invention disclosed herein. Referring now to Fig. 6, a method of manufacturing the simplified transformer will be described with reference also to Fig. 1. As part of the first step 602 of the method 600, the spool 102 of the transformer 100 is formed using an injection molding or other comparable process. Also, the terminals 103 are formed and molded into the terminal rails 111.

In parallel, the core elements 108 and cover element 104 are also formed per steps 603 and 604, respectively. Next, in step 605, the primary and secondary windings 104, 106 are wound onto the spool 102 as shown in Fig 1. The ends 121 of these windings 104, 106 are then terminated to the molded in terminals 103 in step 606 using a dip soldering process which strips the insulation from each wire in the vicinity of the terminal, and then bonds the wire thereto It will be recognized that other forms and methods of termination may be used (including the use of notched terminals upon which the free ends of the windings are wound). Next, in step 608, the core elements 108 are mounted on the spool 102 by inserting the central projections 1 16 into the aperture 112 as shown in Fig. 1. The core elements 108 are interleaved in an alternating fashion when inserted into the aperture as was previously described. When all of the elements 108 are mounted on the spool 102, the cover element 1 10 is then mounted or ' snapped" into the transformer 100 per step 610, specifically so that the ridges 124a 124c engage the bottom edges of the lower core elements 108. The assembly of the transformer 100 is then complete, and may then be electrically tested per step 612.

Note that while recited in a particular order, the order of the steps of the foregoing method 600 may De varied if desired. Additionally, other steps may be added (such as coating the transformer windings, or inspecting/testing the components at various stages of the assembly process) if desired. All sucn permutations and additions are considered to be within the scope of the invention as set forth herein.

While the above detailed description has shown, described, and pointed out novel features of the invention as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the device or process illustrated may be made by those skilled in the art without departing from the spirit of the invention

Claims

WHAT IS CLAIMED IS

1 A transformer comprising a bobbin spool having a primary winding and a secondary winding, the bobbin spool having an opening having a first end and a second end and formed along a central axis of the bobbin spool, a laminar core element having two opposite ends and comprising a plurality of magnetically permeable plates which extend into the passageway of the bobbin spool, and a cover element configured to engage at least the two opposite ends of the laminar core.

2 The transformer of Claim 1 wherein each of the plurality of magnetically permeable plates comprises an E shaped plate with ones of the E shaped plates having middle legs which extend into the opening of the bobbin spool from the first end and other ones of the E shaped plates having a central leg which extends into the opening of the bobbin spool from the second end

3 The transformer of Claim 2 wherein the laminar core element forms a generally rectangular core assembly and the cover element comprises a first side wall, a second side wall, opposite the first side wall, a first end wall, and a second end wall opposite the first end wall and wherein the first and second side walls engage opposite edges of the rectangular core assembly and the first and second end walls engage the remaining opposite edges of the rectangular core assembly

4. The transformer of Claim 1 wherein the plurality of magnetically permeable plates comprises a first core plate comprising a base portion with an outer edge, a central leg extending outwardly from the base portion opposite the outer edge and first and second outer legs also extending outwardly from the base portion opposite the outer edge, the central leg extending into the aperture of the bobbin spool with the first and second outer legs extending along opposite sides of the bobbin spool from the first end, and a second core plate comprising a base portion with an outer edge, a central leg extending outwardly from the base portion opposite the outer edge and first and second outer legs also extending outwardly from the base portion opposite the outer edge, the central leg extending into the aperture of the bobbin spool from the second end with the first and second outer legs extending along opposite sides of the bobbin spool from the second end

5 The transformer of Claim 4 wherein the cover further comprises a first end wall, a second end wall opposite the first end wall a first side wall, and a second side wall opposite the first side wall, wherein the first end wall engages the outer edge of the first core plate the second end wall engages the outer edge of the second core plate, the first side wall extends between the bobbin spool and at least one of the outer legs and the second side wall extends between the bobbin spool and at least another one of the outer legs

6 A laminar core transformer comprising a spool having a central axis and an aperture with first and second ends and extending through the spool along the central axis, a first core plate comprising a base portion with an outer edge, a central leg extending outwardly from the base portion opposite the outer edge and a first end leg and a second end leg, both also extending outwardly from the base portion opposite the outer edge, the central leg extending into the aperture of the spool from the first end with the first and second end legs extending along opposite sides of the spool from the first end; a second core plate comprising a base portion with an outer edge, a central leg extending outwardly from the base portion opposite the outer edge and a first end leg and a second end leg, both also extending outwardly from the base portion opposite the outer edge, the central leg extending into the aperture of the spool from the second end with the first and second end legs extending along opposite sides of the spool from the first end; and a cover comprising a first end wall, a second end wall opposite the first end wall, a first side wall, and a second side wall opposite the first side wall, wherein the first end wall engages the edge of the base portion of the first core element, the second end wall engages an edge of the base portion of the second core element, and the first and second side walls engage one or more of the end legs of the first and second core plates.

7. The laminar core transformer of Claim 6 further comprising a primary winding formed around the spool and a secondary winding also formed around the spool.

8. The laminar core transformer of Claim 6, wherein the first and second side walls are located between the spool and one or more of the end legs of the first and second core plates.

9. The laminar core transformer of Claim 6, wherein the central leg of the first core plate substantially overlays the central leg of the second core plate, the first end leg of the first core plate substantially overlays the first end leg of the second core plate, and the second end leg of the first core plate substantially overlays the second end leg of the second core plate.

10. The laminar core transformer of claim 6, wherein the cover comprises a noncoπductive material.

1 1. A transformer, comprising: a bobbin spool having a primary winding and a secondary winding, the bobbin spool having an opening and formed along a central axis of the bobbin spool with a first end and a second end; a plurality of E shaped magnetically permeable plates, each having a base portion and a central leg, the central leg of each E shaped plate extending into the passageway of the bobbin spool; and a cover element configured to engage at least the base portions of two of the plurality of E shaped plates.

12. The transformer of claim 1 1 , wherein each of the E shaped plates includes a first outer leg and a second outer leg each of which includes an inner edge and the cover element includes a first side wall which engages the inner edge of a first outer leg of at least one of the E shaped plates and a second side wall which engages the inner edge of a second outer leg of at least one of the E shaped plates.

13. A method of fabricating a laminar core transformer comprising: winding primary and secondary windings around a central spool, the central spool having an aperture formed longitudinally through its center; forming a plurality of generally E shaped magnetically permeable core pieces; arranging the E shaped magnetically permeable core pieces in an overlaid fashion with ones of the

E-shaped core pieces having a central leg extending into the aperture of the spool from a first end of the aperture and other ones of the E shaped core pieces having a central leg extending into an opposite end of the aperture; and attaching a cover element to the overlaid E shaped core pieces such that two opposing side walls of the cover are received on outer edges of the overlaid core elements and two other side walls of the cover are received between the outer legs of the core elements and the spool.

14. A method of fabricating a laminar core transformer comprising: winding primary and secondary windings around a central spool, the central spool having an aperture formed longitudinally through its center; forming a plurality of magnetically permeable core pieces; arranging the core pieces in an overlaid fashion with the overlaid core pieces extending through the aperture of the central spool; and attaching a cover element to the overlaid E shaped laminar core pieces such that a first side wall of the cover engages a first edge of the overlaid core pieces and a second side wall of the cover engages a second edge of the overlaid core pieces opposite the first edge.

15. A method of fabricating a laminar core transformer comprising: forming a spool; forming terminals on opposite ends of the spool, forming magnetically permeable core plates with each core plate having a central leg; winding primary and secondary windings onto the spool; terminating ends of the windings at the terminals; inserting the central legs of the core plates into an aperture of the spool with the central legs of the core plates being interleaved; attaching a cover element to the interleaved core plates whereby the core plates are held in a stable configuration.