Transformer core, particularly for supplying power to cold-cathode discharge lamps

Abstract

 A core for electromagnetic transformers, particularly for supplying power to cold-cathode discharge lamps, which is constituted by a plurality of stacked laminations (52), which are in turn constituted by a first central I-shaped element (53) with which two second elements (54a,54b) are laterally associated; the second elements are comb-shaped, so as to form two outer wings (58a,58b) and two inner wings (60a,60b). Each pair of outer wings can be appropriately associated with the free ends of the first central I-shaped element, constituting a so-called shell-type or ironclad magnetic circuit.

Description

[0001] The present invention relates to an electromagnetic transformer particularly suitable for supplying power to cold-cathode discharge lamps.

[0002] Such transformer is advantageously usable for example with cold-cathode lamps filled with neon gas or with other mixtures based on noble gases, such as argon, krypton, helium, xenon, optionally in association with mercury vapors.

[0003] Currently, 50-Hz or 60-Hz transformers provided with a magnetic core equipped with a shunt which is designed to limit the value of the short-circuit current are commonly used for this purpose.

[0004] The intrinsic characteristic of discharge lamps requires the presence of a device which, once the discharge has been triggered, limits the current that flows inside the tube of the lamp.

[0005] This is due to the fact that in almost all resistors crossed by a current there is a direct proportionality between the applied voltage V and the current intensity I, according to the equation V = R I, where R is the characteristic of the resistor.

[0006] The use of ionized gas in these known types of lamps instead creates a situation which is commonly termed "negative resistance", in which the resistance offered by the ionized gas decreases as the current increases, so that the above cited characteristic has to be modified by giving a negative value to the proportionality coefficient R.

[0007] Accordingly, unless the current intensity is adequately controlled and limited, it tends to increase rapidly, causing the overheating of the cathodes and causing them to wear rapidly.

[0008] Known types of transformers dedicated to the cold-cathode discharge lamps therefore have the characteristic of generating high no-load voltages in order to trigger the discharge and of being able to limit it to preset values once gas ionization has begun.

[0009] In order to accomplish this, a transformer of a conventional type for the discharge lamps, known as inherently short-circuit-proof transformer, is designed so as to have a high leakage reactance, which generates the voltage drop from no-load to load so as to protect the lamp and the transformer from the intense currents that would otherwise be generated.

[0010] The limiting reactance is constituted by a magnetic shunt constituted by laminations made of magnetic metal plate which are arranged proximate to the primary winding.

[0011] Currently, the manufacturing process consists in inserting the primary and secondary windings in the lamination pack that constitutes the core and then setting the short-circuit current by adjusting the number of laminations that constitute the shunt.

[0012] The main drawback of these known types of transformers is that they require considerable time for the insertion of the laminations and of other parts made of plastic, paper-like and synthetic materials, such as for example clips of various shapes, insulating cardboards or resins, which are designed to fix, space or insulate the shunt from the core or from the windings.

[0013] Also time-consuming is the subsequent setting of the short-circuit current.

[0014] Moreover, another drawback of these conventional transformers is the poor precision of the short-circuit current, because there are many arbitrary elements and manufacturing inaccuracies which affect the end result; likewise, there is also low uniformity among the performances of individual manufactured known transformers.

[0015] Italian Utility Model Patent no. 0216190 is also known disclosing a core 1 for shell-type transformers which is constituted by a plurality of superimposed laminations, designated by the reference numeral 2, which are in turn constituted by three elements: a central one, designated by the reference numeral 3, which is T-shaped and symmetrical and in which the length of the transverse portion is twice the width of the longitudinal portion; and two lateral elements 4a and 4b, which are L-shaped and in which the length of the longitudinal portion and of the transverse portion are respectively equal to the length of with of the longitudinal portion of the T-shaped element.

[0016] The subject matter of the patent is illustrated in Figures 1 and 2, which show that the width of the longitudinal and transverse portions of the L-shaped elements and the width of the transverse portion of the T-shaped element are constant and equal to half the width of the longitudinal portion of the T-shaped element.

[0017] Although they optimize the manufacture of said laminations by a substantial reduction of waste and a simplification of the manufacturing process, even these known types of transformers have drawbacks similar to the ones described above, since the insertion of the shunts, designated by the reference numeral 5 in Figure 2, occurs after positioning the windings 6, according to the above cited prior art.

[0018] The aim of the present invention is therefore to solve the above mentioned technical problems, eliminating the drawbacks of the prior art by providing an invention which allows to obtain a core for electromagnetic transformers which offers higher precision in the value of the short-circuit current, with a consequent greater uniformity of performance between two individual transformers.

[0019] Within this aim, an object of the present invention is to provide a core which allows to obtain an electromagnetic transformer which does not require parts made of plastic, paper-like or synthetic materials designed to fix, space or insulate the shunt from the core or from the windings.

[0020] Another object of the invention is to provide a transformer which allows savings in terms of materials used and labor.

[0021] Another object is to provide a manufacturing method which minimizes waste by optimizing the process and the production steps.

[0022] Another object is to provide a core for electromagnetic transformer which is structurally simple and has low manufacturing costs.

[0023] This aim and these and other objects which will become better apparent hereinafter are achieved by a core for electromagnetic transformers, particularly for supplying power to cold-cathode discharge lamps, which is constituted by a plurality of stacked laminations, characterized in that said laminations are constituted by a first central I-shaped element with which two second elements are laterally associated, said second elements being comb-shaped so as to form two outer wings, which can be associated with the free ends of said first central element, and two inner wings.

[0024] Further characteristics and advantages of the present invention will become better apparent from the detailed description of a particular embodiment thereof, illustrated only by way of non-limitative example in the accompanying drawings, wherein:

Figures 1 and 2 are schematic sectional views of a conventional transformer, respectively without and with windings and laminations;

Figures 3 and 4 are schematic sectional views of the transformer core of the invention, respectively without and with windings.

[0025] With reference to the figures, the reference numeral 51 designates a core for electromagnetic transformers, particularly for supplying power to cold-cathode discharge lamps.

[0026] The core 51 comprises multiple stacked metallic laminations, generally designated by the reference numeral 52, being conveniently constituted by a first central element 53 which is advantageously I-shaped and with which two second elements, designated by the reference numerals 54a and 54b, are laterally associated.

[0027] Each of the two second elements 54a and 54b is advantageously comb-shaped, with a pair of outer wings 58a or 58b which are connected to the free ends of a central body, respectively designated by the reference numerals 57a and 57b, and protrude in the same direction approximately at right angles to the central body 57a or 57b.

[0028] The pairs of outer wings 58a and 58b have a width which is advantageously approximately equal to the width of the central body 57a or 57b, which is in turn preferably equal to the width of the first central element 53.

[0029] The pairs of outer wings 58a and 58b are associable, two by two, at the opposite sides of the free ends, designated by the reference numerals 59a and 59b, of the first central element 53.

[0030] A pair of inner wings, designated by the reference numerals 60a and 60b and formed monolithically with the central body 57a or 57b, are provided respectively between each pair of outer wings 58a and 58b. The inner wings protrude at right angles from the central body so as to lie on a plane of arrangement which is parallel to the plane of arrangement of the pair of outer wings 58a and 58b.

[0031] The wings that constitute each pair of inner wings 60a and 60b are advantageously equidistant from the pair of outer wings 58a and 58b and from each other, so as to constitute a series of three seats, designated by the reference numerals 61a, 61b and 61c, which are conveniently mutually identical and are suitable to contain the three windings, which are generally designated by the reference numerals 56a, 56b and 56c in Figure 4.

[0032] The width of the pairs of inner wings 60a and 60b, which in the operation of the invention described herein act as a magnetic shunt, must be first determined and then obtained, during manufacture, with high precision.

[0033] In this manner, the production process is accelerated, making adjustment, insertion and calibration of the shunt needless.

[0034] Operation is therefore as follows: with reference to Figures 3 and 4, the structure of the laminations 52 starts off, advantageously by blanking the metal plate, so that it is already provided with a magnetic shunt.

[0035] This solution is possible thanks to the refinement of the manufacturing methods and to the use of materials having a high and uniform quality level.

[0036] Once assembled starting from the first element 53 and the pair of second elements 54a and 54b, the laminations 52 are mutually stacked so as to constitute the core 51.

[0037] Then the windings 56a, 56b and 56c are placed in the respective seats 61a, 61b and 61c, so that said pairs of inner wings 60a and 60b that constitute the shunts are arranged between each winding.

[0038] The structure of the invention is thus symmetrical both along its longitudinal axis and, as regards the connections, with respect to its transverse axis; the connections can be permanent, for example obtained by soldering, or temporary, for example obtained by means of an appropriately provided interlocking coupling.

[0039] This aspect has a positive effect on the mechanical tensions induced by this type of connection method, which in case of transverse asymmetry would lead to a respective asymmetry in the structure and in the magnetic behavior of the core.

[0040] It has thus been found that the invention has achieved the intended aim and objects, a core having been devised which allows to obtain higher precision in the value of the short-circuit current, with consequent greater uniformity of performance between two independent transformers.

[0041] The invention allows to obtain an electromagnetic transformer which requires no parts made of plastic, paper-like or synthetic materials designed to fix, space or insulate the shunt from the core or from the windings, simplifying and therefore reducing the manufacturing and labor costs of the transformer.

[0042] The invention is of course susceptible of numerous modifications and variations, all of which are within the scope of the same inventive concept.

[0043] The materials used, as well as the dimensions of the individual components of the invention, may of course be more pertinent according to specific requirements.

[0044] The disclosures in Italian Patent Application No. TV2000A000087 from which this application claims priority are incorporated herein by reference.

[0045] Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs

Claims

1. A core for electromagnetic transformers, particularly for supplying power to cold-cathode discharge lamps, which is constituted by a plurality of stacked laminations, characterized in that said laminations are constituted by a first central I-shaped element with which two second elements are laterally associated, said second elements being comb-shaped so as to form two outer wings, which can be associated with the free ends of said first central element, and two inner wings.

2. The core according to claim 1, characterized in that each element of said pair of second comb-shaped elements has a shape which is constituted by a central body to the free ends of which said two outer wings are connected, both of said wings protruding in a same direction approximately at right angles to said central body.

3. The core according to claim 1, characterized in that said pair of inner wings is present between each pair of outer wings, said inner wings being provided monolithically with said central body and protruding at right angles thereto so as to arrange themselves on a same plane of arrangement as said two wings.

4. The core according to claim 1, characterized in that said two outer wings are associable in pairs at opposite sides of said free ends of said first I-shaped central element, each one of said central bodies of said comb-shaped elements being arranged approximately parallel to said first I-shaped central element.

5. The core according to claims 1 and 4, characterized in that both wings of each one of said two inner wings are advantageously equidistant from said two outer wings and from each other, so as to constitute a series of three seats which are conveniently mutually identical and are suitable to accommodate first, second and third windings of said electromagnetic transformer.

6. The core according to claim 1, characterized in that said two outer wings have a width which is approximately equal to the width of said central bodies, which is in turn approximately equal to half the width of said first I-shaped central element.

7. The core according to claim 5, characterized in that each one of said two inner wings, by arranging itself between each one of said first, second and third windings, constitutes a magnetic shunt whose value is determined by the respective width.

Drawing