WO2000070926A1

WO2000070926A1 - Planar magnetic elements and assemblies of such elements

Info

Publication number: WO2000070926A1
Application number: PCT/US2000/013057
Authority: WO
Inventors: Paul W. Godek; Louis A. Soto
Original assignee: Nidec America Corporation
Priority date: 1999-05-14
Filing date: 2000-05-12
Publication date: 2000-11-23

Abstract

Planar magnetic elements (18-24) and assemblies of such elements are provided. More particularly, the invention provides one or more planar magnetic elements (18-24) having components unitarily built from and serially connected by a single blank (10) formed from a sheet of conductive material. A frame or header (102) for positioning and supporting one or more planar magnetic elements (18-24) on a substrate having an electrical circuit supported thereon is also provided. The frame (102) provides recesses for locating all of the terminal connectors (54, 55) for the planar magnetic elements (18-24) in a single plane disposed relative to the substrate.

Description

PLANAR MAGNETIC ELEMENTS AND ASSEMBLIES OF SUCH ELEMENTS

Related Applications

This application is a continuation-in-part of co-pending application serial number 09/075,896, filed on May 11, 1998.

Field of the Invention

The present invention relates to planar magnetic elements and assemblies of such elements. More particularly, the invention relates to one or more planar magnetic elements having components unitarily built from and serially connected by a single blank formed from a sheet of conductive material. The invention also relates to a frame for positioning and supporting one or more planar magnetic elements on a substrate having an electrical circuit disposed thereon.

Background of the Invention

Co-pending US patent application, serial number 09/075,896, the disclosure of which is incorporated herein by reference, discloses planar magnetic elements, such as transformers and inductors, having windings formed from a blank of conductive sheet material. Typically, the blank defines a continuous conductive path including a series of substantially closed loops disposed along the path. The blank is folded at preselected locations to position each of the loops in a respective plane and in overlying registration with one another. Such elements provide a number of advantages, including high current carrying capability, low leakage inductance, and a low profile compact design. Accordingly, these elements are particularly suitable for high power applications where space-saving considerations are critical.

Planar magnetic elements constructed with such windings have proven to be quite reliable, being both temperature and vibration stable and repeatable in their manufacture. However, as the demands for even more compact circuit designs and improved reliability increase, there is a need to position planar magnetic elements in very closely packed arrangements within printed circuits, and to further increase reliability by reducing the number of high current connections between these elements and to increase their vibrational stability.

Summary of the Invention

The present invention meets this need by providing, in one aspect, a plurality of components for at least one planar magnetic element which are unitarily built from and serially connected by a blank formed from a sheet of conductive material. The blank defines a continuous conductive path, and selected portions of said path are configured to form the components.

For example, in one embodiment, the conductive path defined by the blank includes two terminal end portions and a plurality of loops disposed along the conductive path between the end portions. The blank is folded at preselected locations on the path to position the loops in overlying registration with one another to define a planar multi-turn winding. According to this particular embodiment, the overlying loops form a multi-turn primary winding for a power transformer, and one of the end portions of the conductive path is configured to form the secondary winding for a current sensing transformer. Thus, two components for two different elements are built from and serially connected by the blank. It should be understood, however, that the invention is in no way limited to this particular embodiment and that the blank can be configured to provide and connect other types of components for planar magnetic elements. For example, the conductive path defined by the blank can be used to form a multi-turn inductor winding, and one of the terminal end portions of the blank can be configured to form a connector for connecting the winding to a conductive pin.

Providing components for planar magnetic elements in accordance with the invention leads to a number of advantages. Unitarily building and serially connecting a plurality of components from a single blank reduces the number of high current connections between the components. This increases the overall reliability of planar magnetic elements comprising such components. Components provided according to the invention also increase the vibration stability of elements including these components, again resulting in substantially more reliable planar magnetic elements. Elements comprising these components are also much easier to assembly, which not only increases reliability but also reduces cost because several components are provided as a single integral unit.

In a second aspect, the invention provides a frame for supporting and positioning a plurality of planar magnetic elements on a substrate having an electrical circuit disposed thereon. The frame defines at least one cavity for receiving the plurality of elements within the frame, and a plurality of recesses for locating connections between the electrical circuit and the elements in a plane fixed relative to the substrate.

In one preferred embodiment, the frame further includes a number of support surfaces for supporting at least one element within the cavity defined by the frame. The plurality of support surfaces are also preferably disposed in a second plane fixed relative to the board for supporting the elements in this second plane. The frame may also define one or more pin receiving aperture for receiving conductive pins. The apertures properly locate the pins for connecting at least one of the planar magnetic elements to a second electrical circuit supported on a second substrate.

Brief Description of the Drawings

Fig. 1 is a top plan view of a blank from which components according to the invention are unitarily built and connected. Fig. 2 is a perspective view of a power transformer primary winding and a current sensing transformer secondary winding formed by folding the blank shown in Fig. 1.

Fig. 3 is a top plan view of a second blank used to form a single-turn power transformer secondary winding. Fig. 4 is a perspective view of the power transformer secondary winding formed from the blank shown in Fig. 3.

Fig. 5 is a partial side section of the power transformer and current sensing transformer secondary winding formed from the blanks shown in Figs. 1 and 3. Fig. 6 is a top view of an assembly of the power transformer shown in Fig. 5 and a current sensing transformer positioned in the frame taught by the invention. Fig. 7 is a side view of the assembly shown in Fig. 6. Fig. 8 is an exploded side view of the assembly shown in Fig. 6. Fig. 9(a) is a top plan view of a third blank from which the winding for a planar magnetic inductor and a connector for a conductive pin are unitarily built. Fig. 9(b) is a top plan view of a fourth blank from which the winding of a second inductor is formed. Fig. 10 is a top view of two inductors having windings formed from blanks such as the blanks shown in Fig. 9 and assembled together in the frame taught by the invention.

Fig. 11 is an exploded side view of the assembly shown in Fig. 10. Fig. 12 is a side view of the assembly shown in Fig. 10.

Detailed Description of the Invention

Fig. 1 illustrates a blank from which components as taught by the invention are unitarily built and serially connected. The blank, generally designated 10, is stamped, punched, cut or otherwise formed from a sheet of conductive material such as copper or aluminum. In the illustrated embodiment, the blank 10 is stamped from a sheet of copper having a thickness of about 0.010 inch. The blank 10 defines a continuous conductive path 12 including a first terminal end portion 14, a second terminal end portion 16, and an alternating series of substantially closed loops 18-24 and connecting portions 26-34. The blank 10 is bent or folded at a number of preselected fold areas 36-50 on the conductive path 12. The fold areas may be scored or otherwise physically marked on the blank 10, or they may simply be designated areas at which the blank is folded. The fold areas are located on the conductive path 12 and the connecting portions 26-34 are dimensioned such that when the blank 10 is folded each one of the loops 18-24 is positioned in a respective plane and in overlying registration with one another. Fig. 2 shows the blank in its completely folded configuration. As shown in Fig. 2 and as just mentioned, when the blank 10 is completely folded into its final configuration, all of the loops 18-24 are positioned in overlying registration with one another. In the illustrated embodiment, the folded blank shown in Fig. 2 forms the primary winding 51 for a power transformer, with the loops 18-24 each defining one of the four individual turns of the winding. The first terminal end portion 14 of the blank 10 is bent or folded at the fold areas 36 and 48 to provide the secondary winding 52 for current sensing transformer 100 (see Figs. 6-8), the winding having the generally L- shaped configuration shown in Fig. 2. The second terminal end portion 16 is folded at the fold areas 46 and 50 to provide a connecting terminal 54 which is soldered to an associated connecting pad on a PC board (not shown) to electrically connect the primary winding to an electrical circuit (also not shown). The secondary winding 52 also includes an connecting terminal 55 which is soldered to an associated connecting pad. It should be understood, however, that the while the final configurations of the windings 51 and 52 are illustrated in Fig. 2, the terminal end portions 14 and 16 are not folded to form the connecting terminals 55 and 54, respectively, until final assembly of the transformers 84 and 100 as discussed further below.

In order to electrically insulate the individual turns or loops 18-24 from one another, an electrically insulating coating is applied to the blank 10 prior to folding. The entire blank is first provided with a tin-lead plating having a thickness of from about 0.0002 to about 0.0003 inches. After the blank 10 has been plated, an insulative parylene coating is applied by gas deposition to the blank, excluding those portions of the blank corresponding to the fold areas 36-50, the terminal end portion 16 and the connecting terminal 55. One such suitable coating is available from Specialty Coatings Systems, Inc., Indianapolis, Indiana. The coating is applied in multiple, essentially mono-molecular layers to a thickness of about 0.002 inches. Applying an insulative coating in this manner insures a uniform coating, even on edge portions of the blank. Alternatively, a urethane coating is applied to a thickness of about 2 mm in a two-stage process. Applying the coating in two stages ensures complete coverage of the blank 10 and provides a coating with a highly uniform thickness.

Fig. 3 illustrates a second blank, generally designated 60, which in the illustrated embodiment is used to form a single-turn secondary power transformer winding that is coupled with the primary winding 51. As in the case of the blank 10, the blank 60 is stamped, punched, cut or otherwise formed from a sheet of conductive material such as copper or aluminum. In the illustrated embodiment, the blank 60 is stamped from a sheet of copper having a thickness of about 0.03 inch. The blank 60 defines a continuous conductive path 62 including a first terminal end 64, a second terminal end 66, and a loop 68 disposed between the two terminal ends. The blank 60 further includes pre-selected folding locations 72-78 which may be scored or otherwise physically marked on the blank, or they may simply be designated areas at which the blank is folded. As noted above, the blank 60 is used to form a single-turn power transformer secondary winding which is shown generally at 70 in Fig. 4. As shown in Fig. 4, the first terminal end portion of the blank 60 is folded at folding locations 72 and 74 to provide a connecting terminal 80, and the second terminal end portion 66 is folded at the folding locations 76 and 78 to provide a connecting terminal 82. The connecting terminals 80 and 82 are soldered to associated connecting pads on a PC board (not shown) to electrically connect the transformer secondary winding 70 within and electrical circuit (also not shown). As in the case of Fig. 2, it should be noted that although the secondary winding 70 is illustrated in Fig. 4 fully folded or bent to form the connecting terminals 80 and 82, the terminals are not actually formed until the power transformer 84 is assembled together with the current sensing transformer as discussed further below.

The transformer secondary winding 70 is provided with an electrically insulating coating in the same manner discussed above with respect to the transformer primary winding 51. Prior to bending or folding the blank 60 at the preselected folding areas, the entire blank is plated with a tin-lead plating having a thickness of from about 0.0002 to about 0.0003 inches. A parylene or urethane coating is then applied to the blank 60, excluding those portions of the blank corresponding to the folding areas 72- 78 and the terminal end portions 64 and 66.

Fig. 5 illustrates a power transformer, generally indicated at 84, which includes the multi-turn primary winding 51 and the single-turn secondary winding 70. As described above, the secondary winding 52 for the current sensing transformer 100 is unitarily built from and serially connected by the blank 10 to the primary winding 51. The power transformer primary and secondary windings are assembled by inserting the secondary winding 70 between turns 20 and 24 of the primary winding 51, such that all of the turns 18-24 and 68 are in overlying registration with on another to define a central aperture 86. The primary and secondary windings are magnetically coupled to an inductive core made, for example, for a ferrite material to form a closed magnetic loop. This is accomplished by mating two generally E-shaped core halves 88, 90 which extend through the central aperture 86. Once the core halves are mated, they are clipped and bonded together to form a whole core 89 and to complete the transformer 84, although it should be understood that both methods of attaching the core halves together are not necessarily required. As shown best in Fig. 6, the fully assembled power transformer and the current sensing transformer secondary winding 52 presents a low profile and a low overall volume, with the planar windings 51 and 70 substantially filling a window defined by the core halves 88, 90. Since the planar secondary winding 70 is disposed between and immediately adjacent to the loops or turns 20 and 24 of the planar primary winding 51 in a close stacking arrangement, enhanced electromagnetic coupling between the primary and secondary windings of the power transformer 84 is provided. The close coupling between the primary and secondary windings reduces the leakage inductance of the power transformer. The planar configuration of the windings 51 and 70 also provides an increase in the surface area and volume of the windings as compared with conventional wire or printed windings. This provides the windings with increased current carrying capability which results in lower conduction losses for the transformer and higher thermal dissipation to prevent overheating than is typical of prior art transformers and other inductive devices which utilize conventional windings. Unitarily building and serially connecting the power transformer primary winding 51 and the current sensing transformer secondary winding 52 eliminates a high current connection between these two components, thus increasing the overall reliability of the planar magnetic elements comprising these components. Building and connecting the windings 51 and 52 in this manner also increase the vibration stability of the transformers 84 and 100 which again results in increased reliability. Further, the power and current sensing transformers can be assembled more simply and easily, because both the primary winding 51 and the secondary winding 52 are provided as an integral unit. This not only increases reliability but also reduces cost.

Figs. 6-8 illustrate the power transformer 84 assembled together with a current sensing transformer, generally designated 100, and received within a frame, generally designated 102, embodying a second aspect of the invention. The frame or header 102 includes a side wall 104 and a base 105, the side wall and base cooperating to define a cavity 106 for receiving the power transformer 84. The frame also defines a second cavity 108 for receiving the primary winding 110 of the current sensing transformer 100. As shown best in Fig. 8, the secondary winding 52 of the transformer 100 passes through a slot 112 defined by the frame, and the connecting terminal 55 of the winding 52 is bent over and received within a recess 114 defined by the base of the frame. A similar slot 115 and recess 116 is provided for connecting terminal 54, as shown best in Figs 6 and 7. Two additional slots 118, 120 and recesses (not shown) defined by the base of the frame 102 are provided for the terminal connectors 80 and 82 of the power transformer secondary winding 70. The base portions of all of the recess are disposed in the same plane. Accordingly, when the connecting terminals are bent over into their respective recesses and against the base portions of the recesses, all of the terminals are also located in this plane. In addition, the location of each recess as defined by the frame 102 is in precise registration with the soldering pads on the PC board on which the frame and transformer assembly will be connected. This arrangement insures that when the frame and transformer assembly is placed onto the PC board, each connecting terminal will be precisely located with respect to the soldering pads. Further, since all of the connecting terminals are disposed in the same plane, accurate and complete co-planar solder connections are obtained.

The frame 102 further defines two pin receiving apertures 122, 124 into which conductive pins 126 and 128 are secured. Leads 130 and 132 from the current sensing transformer primary winding 110 are connected to these pins to complete the assembly of the current sensing transformer 100. It should be understood that the locations of the pin receiving apertures 122 and 124 are precisely located by the frame such that when the pins 126 and 128 are inserted into their respective apertures they are correctly positioned to connect with an electrical circuit disposed on a second PC board positioned above the board on which the transformer assembly is supported.

Accordingly, it will understood from the above that the frame or header 102 provides an effective means of easily assembling planar magnetic elements into a low-profile, compact package. Moreover, the frame precisely locates the connections between the elements supported within the frame and the electrical circuit of which the elements form a part. The frame also provides a means of precisely locating conductive pins and other connectors which connect the planar magnetic elements with other electrical circuitry supported on one or more additional circuit boards, substrates. Referring now to Figs. 9(a) and 9(b), two blanks formed from a sheet of conductive material are illustrated. In the illustrated embodiment, each blank is formed from a sheet of copper having a thickness of about 0.02 inches. The blank, generally designated 140, shown in Fig. 9(a) defines a conductive path including a central portion 142 and three terminal end portions 144, 146, and 148. The central portion 142 of the blank 140 is wound or rolled in a spiral fashion to form the winding 150 of the inductor 152 shown in Figs. 10-12. The terminal end portions 144 and 146 are folded or bent to form terminal connectors for connecting the winding to an electrical circuit, and the terminal end portion 148 is formed into a connector for a conductive pin, as will be discussed below in connection with Figs. 10-12.

The blank, generally designated 154, shown in Fig. 9(b) also defines a conductive path including a central portion 156 and three terminal end portions 158, 160, and 162. The central portion 156 of the blank 154 is wound or rolled in a spiral fashion to form the winding 164 of the inductor 166 shown in Figs. 10-12. The terminal end portions 158, 160 and 162 are folded or bent to form terminal connectors for connecting the winding to an electrical circuit. Figs. 10-12 illustrate the two inductors 152 and 166 received within a frame, generally designated 168. The frame 168 includes a side or outer wall 170, and inner partition 172 and a base 174, all cooperating to define two cavities 176 and 178 for receiving, respectively, the inductors 152 and 166. As shown best in Figs. 10 and 11, the inductor 152 is formed by winding the central portion 142 of the blank 140 in a spiral manner to form the inductor winding 150, with the winding defining a central aperture 180. The winding 150 is magnetically coupled to an inductive core made, for example, from a ferrite material to form a closed magnetic loop. This is accomplished by mating two generally E-shaped core halves 182, 184 which extend through the central aperture 180, as shown best in Figs 10 and 11. Once the core halves are mated, they are clipped and/or bonded together using clips 186, 188 and a layer of epoxy adhesive 190 to complete the inductor 152. The base 174 of the frame 168 defines two support surfaces 192, 193 (one shown in Fig. 12) which extend into the cavity 176 and below the clips 186 and 188. The inductor is inserted into the cavity 176 with the bottom portion of the clips resting on a respective one of the support surfaces. After the inductor 152 has been inserted in the cavity, the terminal end portions 142 and 146 are bent or folded to form terminal connectors 194, 196 for electrically connecting the inductor to an electrical circuit. As in the case of frame 102 discussed above, the base 174 of frame 168 defines two slots or recesses 198 and 200 for receiving the terminal connectors. The base portions of the recess are disposed in the same plane. Accordingly, when the connecting terminals are bent over into their respective recesses and against the base portions of the recesses, the terminals are also located in this plane. In addition, the location of each recess as defined by the frame 168 is in precise registration with the soldering pads on the PC board on which the frame and inductor assembly will be connected. As noted above, this arrangement insures that when the frame and inductor assembly is placed onto the PC board, each connecting terminal will be precisely located with respect to the soldering pads. Further, since all of the connecting terminals are disposed in the same plane, accurate and complete co-planar solder connections are obtained.

Referring now in particular to Fig. 10, the terminal end portion 148 of the winding 150 is formed into a collar-shaped connector 202 for receiving and electrically connecting the inductor winding to a conductive pin (not shown). Thus, two components for a planar magnetic element, an inductor winding and a pin connector are unitarily built and serially connected by the blank 140, in accordance with the teachings of the invention. As discussed above, providing multiple components in this manner decreases the number of high current connection, increases vibration stability and increase overall reliability. The inductor 166 is formed in the same manner discussed above with respect to the inductor 152. The central portion 156 of the blank 154 is wound in a spiral manner to form the inductor winding 164, with the winding defining a central aperture 204. The winding 164 is magnetically coupled to an inductive core to form a closed magnetic loop by mating two generally E-shaped core halves 206, 208 which extend through the central aperture 204, as shown best in Figs 10 and 11. In the illustrated embodiment the core halves are both clipped and bonded together using clips 210, 212 and a layer of epoxy adhesive 214, although it should be understood that both methods of attachment are not required. Two support surfaces 216, 218 (one shown in Fig. 12) are defined by the base 174 and extend into the cavity 178 and below the clips 210 and 212. The inductor 166 is inserted into the cavity 178 with the bottom portion of the clips resting on a respective one of the support surfaces. All of the support surfaces 192, 193, 216, and 218 are disposed in the same plane. Accordingly, when the inductors 152 and 166 are supported on these surface they are also disposed in the same plane, which provides the entire assembly with a uniform package height.

After the inductor 152 has been inserted in the cavity, the terminal end portions 158, 160 and 162 are bent or folded to form terminal connectors 220, 222 and 224 for electrically connecting the inductor to an electrical circuit. Three recesses 226, 228 and 230 for receiving the terminal connectors are defined by the base 174, and the base portions of these recess are disposed in the same plane as those of recesses 198 and 200. Accordingly, as in the case of inductor 152, when the connecting terminals 220, 222 and 224 are bent over into their respective recesses and against the base portions of the recesses, the terminals are also located in this plane. In addition, the location of each recess as defined by the frame 168 is in precise registration with the soldering pads on the PC board on which the frame and inductor assembly will be connected. The base 174 of the frame 168 defines two pin receiving apertures 232 and 234 into which conductive pins 236 and 238 are secured. Leads 240 and 242 from the inductor winding 164 are connected to these pins to complete the assembly of the inductor. Again, it should be understood that the locations of the pin receiving apertures 232 and 234 are precisely located by the base 174 of the frame such that when the pins 236 and 238 are inserted into their respective apertures they are correctly positioned to connect the inductor 166 with an electrical circuit disposed on a second PC board positioned above the board on which the inductor assembly is supported.

As will be understood from the foregoing, use of the frame or header 168 provides an easily assembled densely packed, low-profile package of planar magnetic elements. The frame also precisely locates the connections between the elements supported within the frame and the electrical circuit of which the elements form a part, and provides a means of precisely locating conductive pins and other connectors which connect the planar magnetic elements with other electrical circuitry supported on one or more additional circuit boards.

As will be recognized by those skilled in the art, numerous modifications can be made to the above-described embodiments without departing from the scope of the invention. Accordingly, the preceding portion of the specification is to be taken in an illustrative, as opposed to a limiting sense.

Claims

CLAIMS:

1. A plurality of components for at least one planar magnetic element, said components being unitarily built from and serially connected by a blank formed from a sheet of conductive material, said blank defining a continuous conductive path, selected portions of said path being configured to form said components.

2. The plurality of components of claim 1 , wherein the blank includes a plurality of loops disposed along the conductive path, said blank being foldable at preselected locations on the path to position the loops in overlying registration to one another to define a planar multi-turn winding.

3. The plurality of components of claim 2, wherein the blank is configurable at selected other locations to define at least a second winding serially connected to the planar magnetic winding.

4. The plurality of components of claim 3, wherein the planar magnetic winding defines the primary winding of a power transformer and the second winding defines the secondary winding of a current sensing transformer.

5. The plurality of components of claim 2, wherein the blank is configurable at selected other locations to define a connector for connecting the winding to a conductive pin.

6. A frame for supporting and positioning a plurality of planar magnetic elements on a substrate having an electrical circuit disposed thereon, said frame defining at least one cavity for receiving the plurality of elements within the frame, and a plurality of recesses for locating connections between the electrical circuit and the elements in a plane fixed relative to the substrate.

7. The frame of claim 7, wherein the frame further comprises a plurality of support surfaces for supporting at least one element within the at least one cavity defined by the frame.

8. The frame of claim 6, wherein at least one of the elements includes a winding having terminal ends, with at least one of the terminal ends being received within one of the recesses.

9. The frame of claim 1 , wherein the frame defines at least one pin receiving aperture for receiving a conductive pin, said pin connecting at least one of the planar magnetic elements to a second electrical circuit supported on a second substrate.

10. The frame of claim 1 , wherein the plurality of support surfaces are disposed in a second plane fixed relative to the substrate for supporting the elements in said second plane.