ELECTRONIC TRANSFORMER

FIELD OF THE INVENTION

[0001] The invention relates to an ET (electronic transformer), and more particularly, to an ET in which a face-to-face design of a primary winding and a secondary winding is employed and a bobbin is only arranged on the secondary winding side.

BACKGROUND OF THE INVENTION

[0002] Electronic transformers are used in a variety of applications, for example in power supply units for halogen lamps. In such application, an input line voltage (e.g. the typical mains voltage for China and most European countries is 220-240 volts while 100-120 volts are typical values for American countries) is transformed into an output voltage of 12 or 24 volts.

[0003] Currently, as the size of the electric devices such as halogen lamp is increasingly miniaturized and the electro safety requirement thereof is increasingly strict, the demand on the size and the insulation safety is getting higher.

[0004] According to IEC 61347-2-2 and SELV requirements, the ET must fulfill the insulation and other safety requirements between its primary winding and secondary winding and between the winding and its core, etc. In particular, the insulation requirement between the secondary winding and the core is higher as compared to that between the primary winding and the core.

[0005] One known apparatus that can meet such requirement is a bobbin as shown in Fig. 1 for separating the primary winding and the secondary winding. However, in the transformer as shown in Fig. 1, since the bobbin is arranged on the entire core, the structure of the transformer is inevitably complicated and the size thereof becomes too large. In addition, since the core is substantially covered by the winding, the leak inductance of the transformer during operation is too small, thus a power semiconductor is easily damaged when a short circuit occurs in the product. As a result, the reliability of the transformer itself and also of other electronic devices in the entire product is decreased, that is, the short circuit characteristic of the transformer is affected.

[0006] The term "short circuit characteristic" used herein means the amount of the dissipation of the transformer itself and of other electronic devices in the entire product in a short circuit text. The amount of the dissipation is evaluated by a resulting temperature, the lower the temperature is, the lower the dissipation is and thus the better the short circuit characteristic is.

[0007] Another prior art transformer is shown in Fig. 2. As shown in Fig. 2, a primary winding and a secondary winding of such transformer are arranged face-to-face, thus the leak inductance of the transformer can be increased appropriately and the short circuit characteristic thereof is improved to a certain extent. However, since the secondary winding directly contacts with a core, a potential safety problem exists inevitably, thus such transformer is not approved the related institutes (such as VDE) in some countries (such as Germany or other European countries).

[0008] The invention is intended to solve the above problems existing in the prior art.

SUMMARY OF THE INVENTION

[0009] In view of the above mentioned problems, the object of the invention is to provide an ET. The ET includes: a core; a primary winding; and a secondary winding, wherein the primary winding and the secondary winding are wound around the core, arranged face-to-face, and spaced apart from each other by a certain distance along the core. The ET further includes an insulating element that is arranged on the secondary winding side of the core and between the core and the secondary winding, such that the core and the secondary winding are mutually separated.

[0010] Preferably, the core is a toroid.

[0011] Preferably, the angles on the toroid that are occupied by the primary winding and the secondary winding are each between 90o to 150o. More preferably, the angles are 120o. [0012] Preferably, the insulating element is a bobbin. Alternatively, the insulating element is an insulating tape wound around the core.

[0013] Preferably, the bobbin is made up of an upper portion and a lower portion which are separately formed and each have a U-shaped cross-section.

[0014] Preferably, the upper portion includes: a first body; upper steps formed at lower edges of inner and outer sides of the first body; and upper flanges protruding outward and formed at the entire rims of both ends of the first body. In addition, the lower portion includes: a second body; lower steps formed at upper edges of inner and outer sides of the second body; and lower flanges protruding outward and formed at the entire rims of both ends of the second body.

[0015] Preferably, the upper step and the lower step are complementary in shape, such that when the upper portion and the lower portion are assembled together by inserting the upper step of the upper portion into the lower portion, the upper portion and the lower portion can be closely fitted together.

[0016] Preferably, a fixing protrusion is provided on the upper step, and a fixing recess that is snap fitted with the fixing protrusion is provided on the lower step.

[0017] In the above described ET, since the above described winding face-to-face design is employed, as compared to the traditional transformer whose core is substantially completely covered by the winding, the ET according to the invention may moderately increase the leak inductance during the operation, thereby a power semiconductor is less possible to be damaged when a short circuit occurs in the product. In this way, the dissipation of the transformer itself and also of other electronic devices in the entire product can be reduced, that is, the short circuit characteristic of the transformer can be improved.

[0018] In addition, in the above described ET, since the above described bobbin partial arrangement (i.e. the arrangement in which the bobbin is only arranged on the secondary winding side whose insulation requirement is higher) is employed, on the one hand, the insulation between the secondary winding and the core can be appropriately increased, which allows the transformer to fulfill IEC 61347-2-2 and SELV requirements or to be approved by the Institutes of Electrical Engineers of some countries. On the other hand, since the bobbin is only arranged on the secondary winding side whose insulation requirement is higher, the transformer may be simpler in structure and more compact in dimension, which allows the manufacturing and shipping costs of the transformer to be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[001.9 J Below, exemplary but non- limiting embodiments of the invention are described with reference to the drawings, wherein like reference numbers are used to indicate like members, and wherein:

[0020] Fig. 1 shows a traditional transformer;

[0021] Fig. 2 shows another traditional transformer;

[0022] Fig. 3 shows in a top view a transformer according to an exemplary embodiment of the invention;

[0023] Fig. 4 shows in a perspective view the transformer in Fig. 3;

[0024] Fig. 5 shows in a plan view a bobbin used in the transformer according to the exemplary embodiment of the invention;

[0025] Fig. 6 shows in a sectional view the bobbin in Fig. 5;

[0026] Figs. 7 and 8 show perspective views of the bobbin in Figs 5 and 6 viewed from different directions, respectively.

DETAILED DESCRIPTION OF THE INVENTION [0027] Below, an exemplary embodiment of the invention is described in details with reference to the drawings.

[0028] Figs. 3 and 4 are a top view and a perspective view showing an ET (electronic transformer) according to the exemplary embodiment of the invention, respectively. As shown, the ET is generally denoted by reference number 100.

[0029] The ET 100 includes a core 1, a primary winding (primary side) 2 and a secondary winding (secondary side) 3. In this embodiment, the core 1 is a toroid (annular core), and preferably, the core 1 is in the form of a ferrite core and treated with a suitable insulating coating. The primary winding 2 and the secondary winding 3 are wound around the core 1 , respectively, in other words, the windings are formed by winding an electrically conductive wire around the core. The wire may be either the single wire type or the braided (i.e. Litz wire) type, and preferably, the wire is an enameled copper wire. In this embodiment, as best shown in Fig. 3, the primary winding 2 and the secondary winding 3 are arranged in a face-to-face manner. In the case of employing the toroid, the primary winding 2 and the secondary winding 3 are preferably arranged symmetrical about the center of the toroid. Further, in this embodiment, the primary winding 2 and the secondary winding 3 are spaced apart from each other by a certain distance in the circumferential direction of the core. That is, angles (angular regions) on the toroid that are occupied by the primary winding 2 and the secondary winding 3 may each be between 90o to 150o, preferably between 100ο to 140o, more preferably between HOo to 130o, and most preferably 120o.

[0030] While the toroid is shown in the drawings, it should be understood that the core of the ET according to the invention may also employ any other suitable shapes. In addition, while it is shown in the drawings that the numbers of the primary winding and the secondary winding are each one, it should be understood that any other suitable numbers of the primary winding and the secondary winding of the ET according to the invention are possible.

[0031] With the above described winding face-to-face design, as compared to a traditional transformer whose core is substantially completely covered by a winding, the ET according to the invention may moderately increase the leak inductance during the operation, thereby a power semiconductor is less possible to be damaged when a short circuit occurs in the product. In this way, the dissipation of the transformer itself and also of other electronic devices in the entire product can be reduced, that is, the short circuit characteristic of the transformer can be improved. [0032] Further, the ET according to the exemplary embodiment of the invention includes a bobbin 4, and the bobbin 4 is only arranged on the secondary winding 3 side while no bobbin is provided between the primary winding 2 and the core 1. That is, the bobbin 4 is partially arranged with respect to the entire core 1. In this embodiment, the bobbin 4 is directly enclosed on a portion of the core 1 corresponding to the secondary winding 3 side, and then the secondary winding 3 is wound around the bobbin 4, as a result, the secondary winding 3 is prevented from "directly" contacting with the core 1. Also, in this embodiment, as shown in Fig 3 or 4, the extension of the bobbin 4 on the core 1 is substantially the same as, or slightly larger than, the extension of the secondary winding 3 on the core 1. The bobbin 4 may be made of any type of electrically insulating materials which are currently used, including plastics such as bakelite, PET, PBT, FR-530 or nylon, and the bobbin 4 has a thickness that meets the insulation safety standard.

[0033] With the above described bobbin partial arrangement (i.e. the arrangement in which the bobbin is only arranged on the secondary winding side whose insulation requirement is higher), on the one hand, the insulation between the secondary winding and the core can be appropriately increased, which allows the transformer to fulfill IEC 61347-2-2 and SELV requirements or to be approved by the Institutes of Electrical Engineers of some countries. On the other hand, since the bobbin is only arranged on the secondary winding side whose insulation requirement is higher, the transformer may be simpler in structure and more compact in dimension, which allows the manufacturing and shipping costs of the transformer to be reduced.

[0034] Below, the bobbin according to an exemplary embodiment of the invention is described with reference to Figs 5-8.

[0035] As shown, in this embodiment, the bobbin 4 includes an upper portion 41 and a lower portion 42 which are separately formed and both of which have a U-shaped cross-section. In use, the upper portion 41 and the lower portion 42 are assembled together so as to form the hollow cylindrical bobbin 4. In this embodiment, the bobbin 4 is formed to have a profile that matches the profile of at least a portion of the core 1. The upper portion 41 includes: a body (a first body) 45; upper steps 49 formed at lower edges of inner and outer sides of the body 45; and upper flanges 53 protruding outward and formed at the entire rims of both ends of the body 45. Correspondingly, the lower portion 42 includes: a body (a second body) 46; lower steps 50 formed at upper edges of inner and outer sides of the body 46; and lower flanges 53 protruding outward and formed at the entire rims of both ends of the body 46. The height of the flange is substantially the same as, or slightly larger than, the height of the winding, such that the winding operation of the wire during the production is facilitated and the resulting winding does not slide out of the bobbin.

[0036] In this embodiment, the upper step 49 and the lower step 50 are complementary in shape. That is, the length LI of the upper step 49 corresponds to the length L2 of the lower step 50, in addition, the width Dl of the upper step 49 corresponds to the width of a shoulder 62 of the lower step 50, and vice versa. In this way, when the upper portion 41 and the lower portion 42 are assembled together by inserting the upper step 49 of the upper portion 41 into the lower portion 42, the upper portion 41 and the lower portion 42 can be closely fitted together, and in the resulting bobbin, the inner and outer surfaces at the junctures exhibit flush. In one embodiment, a fixing protrusion 57 that is for example integrally formed with the body 45 is provided on the upper step 49, and a fixing recess 58 that is snap fitted with the fixing protrusion 57 is provided on the lower step 50. In this way, the upper portion 41 and the lower portion 42 can be fixed together without any additional fastener, which greatly facilitates the assembly of the bobbin.

[0037] In one embodiment, as an alternative to the above described bobbin, an insulating tape wound around the core may be used. Of course, it should be understood to those skilled in the art, in addition to this, any other suitable insulating elements may also be used.

[0038] Any reference in this specification to "exemplary embodiment", "this embodiment", "one embodiment, etc., means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with any embodiment, it is submitted that it is within the purview of those skilled in the art to effect such feature, structure, or characteristic in connection with other ones of the embodiments.

[0039] While the invention has been described in connection with exemplary embodiments, it should be understood that various modifications may be made to the exemplary embodiments by those skilled in the art without departing from the scope defined by the appended claims.