MODULAR HIGH FREQUENCY POWER TRANSFORMER

Abstract: A miniature high frequency power transformer comprises first and second "E" shaped ferrite core halves surrounding mating inner and outer modular transformer bobbins having formed thereon respectively the primary and secondary windings of the transformer. The inner and outer modular transformer bobbins are positioned such that the inner transformer bobbin is inserted into the outer transformer bobbin with the secondary windings surrounded by the primary windings. When assembled, the inner modular transformer bobbin has a protrusion that extends axially therefrom through the outer bobbin and terminates in first core retaining ears at one end of the transformer. Second core retaining ears extend from the opposite end of the transformer, and both ears receive the "E" shaped core halves, maintained in position on the transformer by bonding.

Description: TECHNICAL FIELD The present invention relates generally to power transformers and more particularly to miniature, high frequency, modular power transformers. BACKGROUND ART Conventional high frequency power transformers that require high voltage isolation between primary and secondary windings are usually manufactured as an integral assembly that requires labor intensive winding of the primary and secondary windings, leading to high costs. Conventional devices further require potting or special coating for the transformer to meet standard industry dielectric withstand specifications, such as U.L. 1244, ANSI C39.5 or IEC 348. Therefore, it would be desirable to provide a miniature high frequency power transformer that is compact and inexpensive to manufacture, that exhibits good magnetic coupling and high voltage isolation to meet standard industry dielectric withstand specifications and that utilize modular components. EP-A-0 138 014 describes a power transformer comprising: a highly permeable transformer core; outer and inner modular transformer bobbins comprising respectively a first shank and a second shank; said first shank having a plurality of flanges formed thereon, said flanges establishing an area having first windings of said transformer, said first shank having a first aperture formed therethrough; said second shank being slightly smaller in diameter than the diameter of the first aperture formed in the first shank, and having an area thereon having second windings of said transformer, said second shank having a second aperture extending axially therethrough; said second shank of said inner modular transformer bobbin being inserted into said first aperture formed in said first shank. In accordance with the present invention there is provided a power transformer of the above type characterised in that said transformer is a miniature high-frequency power transformer; said transformer further comprises first core retaining ears extending from one end of said transformer; said first aperture comprises an end wall having a protrusion extending therefrom axially through said first aperture and terminating at the other end of said transformer at second core retaining ears; said second aperture is slightly larger in diameter than the diameter of the protrusion formed in the first shank; and said protrusion extends from said first shank inserted into said second aperture formed in said second shank so that said second windings on said second shank are within said first windings formed on said first shank and said highly permeable core being supported within said first and second core retaining ears and surrounding said inner and outer modular transformer bobbins. The modular design of the miniature high frequency power transformer minimizes assembly errors that may compromise protective dielectric spacings necessary to meet industry safety standards. Furthermore, forming the windings on the inner and outer modular transformer bobbins can be carried out in advance by automated equipment further minimizing human error and reducing costs. No transformer potting or special coating is required in the assembly of the present invention. Still other advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the invention is shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modification in various obvious respects, all without departing from the invention. Accordingly, the drawing and description are to be regarded as illustrative in nature, and not as restrictive. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of an assembled transformer in accordance with an embodiment of the present invention; FIG. 2 is an exploded view of a transformer of FIG. 1, showing inner and outer modular transformer bobbins and corresponding ferrite core halves; and FIG. 3 is an enlarged cross sectional side view of the inner and outer modular transformer bobbins before assembly. BEST MODE FOR CARRYING OUT THE INVENTION Referring to FIGs. 1-3, a miniature high frequency power transformer 100, in accordance with a preferred embodiment of the invention, comprises an outer modular transformer bobbin 200 having primary windings 218 formed thereon, an inner modular transformer bobbin 202 having secondary windings 220 thereon and first and second ferrite core halves 102 and 103 surrounding both bobbins. The outer modular transformer bobbin 200 further has a primary shank portion 230 with a first flange 302 at one end of the shank, a second flange 226 centered on the shank, and a third flange 224 on the opposite end. The two bobbins 200, 202 are preferably formed of a plastic material. The first flange 302 has first transformer core retaining ears 304 (FIG. 3) formed thereon that extend axially from one end of transformer face 320. Second flange 226, formed midway between flanges 302 and 224 on shank 230, creates an area 315 that receives the primary windings 218. Third flange 224 is formed on the shank 230 with an aperture 208 therein that is defined by wall 208a (FIG. 2). A protrusion 205 extends from an end wall 302a on flange 302 axially through aperture 208, to form second core retaining ears 204 at the opposite end of the transformer. Inner modular transformer bobbin 202 has a secondary shank portion 214 that receives secondary windings 220 at an area 316. First mating flange 212 is formed on secondary shank 214 with aperture 206 therein. It should be noted from FIG. 3 that aperture 206 has the same shape and is slightly larger in diameter than the diameter of protrusion 205. A secondary retaining wall 210a is formed on secondary shank 214 by a flange 202 having secondary lips 210b thereon. The secondary lips 210b (See FIG. 2) have the same inside dimensions as third flange 224 on the outer transformer bobbin 200. Aperture 206 of wall 210a has a diameter slightly larger than the diameter of protrusion 205. Both the outer modular transformer bobbin 200 and the inner transformer bobbin 202 have electrically conductive mounting pins 110 thereon that are capable of mounting and electrically interconnecting the miniature high frequency transformer 100 to a circuit board (not shown). "E" shaped ferrite core halves 102 and 103 (FIG. 2) are identical to each other and provide a highly efficient flux path between the primary windings 218 and secondary windings 220. Ferrite core halves 102 and 103 further act to maintain outer transformer bobbin 200 and inner transformer bobbin 202 assembled together to form the miniature high frequency transformer 100 as hereinafter described. In the assembly of the preferred embodiment of the invention shown in FIG. 1, referring additionally to the enlarged view of the inner and outer modular transformer bobbins 200 and 202 shown in FIG. 3, bobbins 200 and 202 are positioned such that first mating flange 212 on inner modular bobbin 202 faces third flange 224 on outer modular transformer bobbin 200. Protrusion 205 on bobbin 200 is then aligned with aperture 206 on bobbin 202, and first mating flange 212 is inserted into aperture 208 on bobbin 200 such that shank 214 interfits with aperture 208. Protrusion 205 is moved axially through aperture 206 until first mating flange 212 comes into contact with primary retaining wall 302a; likewise third flange 224 is adjacent secondary retaining wall 210a and lips 210b. First core retaining ears 304 (FIG. 3) extend from primary face 320 and second core retaining ears 204 extend from secondary face 330. Center portion 102a of first core half 102 (FIG. 1) is next inserted into aperture 205 at primary face 320 until first core half 102 is retained by first core retaining ears 304. Similarly, center portion 103a of second core half 103 is inserted into aperture 206 at secondary face 330 of inner transformer bobbin 202 until core half 103 is retained by second core retaining ears 204, and core faces 102a and 103a on the first and second ferrite core halves, respectively, are face to face, to be bonded together to form the assembly of FIG 1. It should be understood that when miniature high frequency transformer 100 is thus assembled, secondary windings 220 are contained within primary windings 218 formed on outer modular transformer bobbin 200 and both primary windings 218 and secondary windings 220 are surrounded by first and second ferrite core halves 102 and 103 (See FIG. 1). Of course, the positions of the primary and secondary windings can be interchanged. This close fitting relationship between the windings and the core halves maximizes coupling of the windings to the highly permeable ferrite core and minimizes flux leakage. Once assembled, first and second ferrite core halves 102 and 103 are bonded together by any suitable bonding agent (not shown) applied to first and second core faces 102a and 103a. There has accordingly been described a miniature high frequency power transformer wherein magnetic coupling is maximized by the utilization of low cost and easily assembled modular transformer bobbins. Modular assembly and close manufacturing tolerances meet or exceed industry safety standards for high voltage isolation for high frequency power transformers. In this disclosure, there is shown and described only the preferred embodiment of the invention, but, it is to be understood that the invention is capable of use in various other combinations and environments and is capable of changes or modifications within the scope of the claims.

Claims: A power transformer (100) comprising: a highly permeable transformer core (102,103); outer and inner modular transformer bobbins (200,202) comprising respectively a first shank (230) and a second shank (214); said first shank (230) having a plurality of flanges (302,226,224) formed thereon, said flanges establishing an area having first windings (218) of said transformer (100), said first shank (230) having a first aperture (208) formed therethrough; said second shank (214) being slightly smaller in diameter than the diameter of the first aperture (208) formed in the first shank (230), and having an area (316) thereon having second windings (220) of said transformer (100), said second shank (214) having a second aperture (206) extending axially therethrough; said second shank (214) of said inner modular transformer bobbin (202) being inserted into said first aperture (208) formed in said first shank (230); characterised in that: said transformer (100) is a miniature high-frequency power transformer; said transformer (100) further comprises first core retaining ears (304) extending from one end of said transformer (100); said first aperture (208) comprises an end wall having a protrusion (205) extending therefrom axially through said first aperture (208) and terminating at the other end of said transformer (100) at second core retaining ears (204); said second aperture (206) is slightly larger in diameter than the diameter of the protrusion (205) formed in the first shank (230); and said protrusion (205) extends from said first shank (230) inserted into said second aperture (206) formed in said second shank (214) so that said second windings (220) on said second shank (214) are within said first windings (218) formed on said first shank (230); said highly permeable core (102,103) being supported within said first (304) and second (204) retaining ears and surrounding said inner and outer modular transformer bobbins. A transformer according to claim 1, wherein said first shank (230) and said second shank (214) comprise respectively a primary shank and a secondary shank and wherein said first windings (218) and said second windings (220) comprise respectively primary windings and secondary windings of said transformer (100). A transformer according to claim 1, wherein said first shank (230) and said second shank (214) comprise respectively a secondary shank and a primary shank and wherein said first windings (218) and said second windings (220) comprise respectively secondary and primary windings of said transformer (100). A transformer according to any preceding claim, wherein the highly permeable transformer core comprises first (102) and second (103) identical core halves joint together around said inner and outer transformer bobbins (200,202). A transformer according to claim 4, wherein said core halves (102,103) are retained in said first (304) and second (204) retaining ears respectively. A transformer according to claim 4 or claim 5, wherein said core halves (102,103) are comprised of ferrite. A transformer according to anyone of claims 4 to 6, wherein said first and second core halves (102,103) are bonded together. A transformer according to any preceding claim, further comprising means (110) for mounting said transformer (100) on a circuit board. A transformer according to claim 8, wherein said means for mounting said transformer (100) comprises a plurality of pins (110), at least one of said pins being electrically conductive. A transformer according to any preceding claim, wherein said outer and inner transformer bobbins (200,202) are formed of a plastic material. A transformer as claimed in any preceding claim, wherein said transformer core comprises first (102) and second (103) "E" shaped ferrite core halves surrounding said outer and inner transformer bobbins (200,202) with central stems of said core halves (102, 103) inserted in said first (208) and second (206) apertures respectively.

Inventors: ENG, BENJAMIN, WINSOR, MARGARET E.
Applicants: JOHN FLUKE MFG. CO., INC.
Application year: 1989
Main classification: H01F27
IPC codes: H01F27, H01F30