The transformer with TIW Patent/TABUCHI ELECTRIC CO.,LTD./


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The transformer with TIW patent

The present invention generally relates to a transformer for use in, for example, a switching power source device and, more particularly, to the transformer for a high frequency power source with the triple insulated wire meeting the safety requirement of the world. A transformer for a high frequency power source which is designed to be compact in size is of a structure wherein primary and secondary windings are wound around a bobbin in an overlapping relation. This type of the transformer must satisfy requirements stipulated in the safety standards in connection with electric insulation between the primary and secondary winding and space-creepage (creeping) for insulation. In the transformer which utilizes, for each of the primary and secondary windings, a normal insulated winding wire having a single layer of an insulating film deposited on the surface of the winding wire such as, for example, an enamel-coated winding wire in order for the transformer to satisfy the safety standard requirements, a length of barrier tape made of epoxy is wound around each of opposite ends of a coil bobbin and the primary and secondary windings are wound in a number of turns around a portion of the coil bobbin between the taped ends of the coil bobbin with an electrically insulating tape intervening between each neighboring layers of the turns of the primary and secondary windings. Thus, the space-creepage that satisfies the safety standard requirements is secured between the primary and secondary windings in the presence of the barrier tape at each of the opposite ends of the coil bobbin and, also, electric insulation between the neighboring layers of turns of the primary and secondary windings is established by the insulating tape intervening therebetween.
The transformer of the type discussed above requires a substantial space for winding of the lengths of barrier tape on the opposite ends of the coil bobbin and, therefore, the coil bobbin used therein must be bulky in size to accommodate the length of barrier tape. For this reason, when it comes to the use of the transformer of the above discussed type in the high frequency power source which is generally required to be compact in size, the transformer fails to satisfy the requirement. In addition, assemblage of the transformer of the above discussed type requires an additional process step of winding the lengths of barrier tape on the respective ends of the coil bobbin for each layer of turns of the windings, resulting in an inefficient workability and also in a substantial increase in manufacturing cost.
In view of the foregoing, the transformer in which no barrier tape is employed and, instead, a primary winding is prepared from a winding wire having reinforced insulation such as, for example, a triple insulated winding wire, has been suggested. This suggested transformer is shown in FIG. 10 and will now be discussed in detail with reference to FIG. 10. The transformer shown in FIG. 10 includes a coil bobbin 5 has an EI-shaped core assembly 6 including a generally E-shaped core 6a and a generally I-shaped core 6b assembled together to define a magnetic circuit A primary winding 1 includes winding portions 1a and 1b wound around the coil bobbin 5 and has an intermediate tap wire drawn between the winding portions 1a and 1b and, so far shown in FIG. 10, forms first and fourth layers in a direction transversely outwardly of the coil bobbin 5. Secondary windings 2a and 2b and a base winding 3, both prepared from an enamel-coated winding wire, are also wound around the coil bobbin 5. This primary winding 1 is prepared from a triple insulated winding wire which, in an assembled condition, provides a required electric insulation between the primary winding 1 and both of the secondary and base windings 2a, 2b and 3. Each neighboring layers of turns of each of the windings 1a, 1b, 2a, 2b and 3 are insulated from each other in the presence of a length of insulating tape 4.

The Subject that the invention solves

Connection of the winding wire having the insulating layer of the three-layered structure which forms the primary winding 1, with terminal pins 8A associated with the primary winding 1 is generally carried out by passing opposite ends of the primary winding through lead-out grooves 5c defined in one of opposite collars, e.g., the collar 5a, of the coil bobbin 5 towards the respective terminal pins 8A and then soldering them to the terminal pins 8A as at H. For this reason, the three-layered insulation at a portion S1 of each of the opposite ends of the primary winding 1, where soldering is effected and which is shown as hatched with horizontal lines in FIG. 7, tends to be thermally deteriorated during the soldering process to such an extent as to result in a considerable reduction in electrically insulating property. The three-layered insulation on the triple insulated winding wire when its insulating property is reduced loses a function of securing the necessary space-creepage distance.

The Means to solves the subject
To accomplish this and other objects of the present invention, the present invention provides a transformer which comprises a bobbin having a longitudinal axis and also having a through-hole defined therein so as to extend axially thereof, a core member inserted in the through-hole, an intermediate collar mounted on the bobbin at a location generally intermediate of the length of the bobbin with said bobbin consequently having main and auxiliary bobbin regions defined on respective sides of the intermediate collar in a direction axially of the bobbin, and primary and secondary windings being wound around the bobbin in an overlapping relation. At least one of the primary and secondary windings is prepared from a winding wire having reinforced insulation. Opposite ends of said at least one of the primary and secondary windings are soldered to terminal pins after having traversed the auxiliary bobbin region.
In this transformer according to the present invention, either some of the turns of said at least one of the primary and secondary winding or a third winding being wound around the auxiliary bobbin region while the remaining turns of said at least one of the primary and secondary windings and the other of the primary and secondary windings are wound around the main bobbin region. In a preferred embodiment of the present invention, the intermediate collar is formed with a plurality of insertion grooves inwardly recessed from an outer edge of the intermediate collar for passage of either the primary winding or the secondary winding so as to extend from the main bobbin region to the auxiliary bobbin region. Alternatively, the intermediate collar may be formed with lead-out grooves each extending from an inner portion to the outer edge of the intermediate collar and inclined downwardly towards the auxiliary bobbin region for passage of either the primary winding or the secondary winding so as to extend from the main bobbin region to the auxiliary bobbin region.
According to another preferred embodiment of the present invention, the bobbin has first to fourth side faces, the first and second side faces being opposite to each other in a direction radially outwardly of the bobbin while the third and fourth side faces are opposite to each other in the direction radially outwardly of the bobbin. The bobbin has an additional collar mounted thereon adjacent the auxiliary bobbin region, and first and second rows of terminal pins associated respectively with the first and second windings are secured to the additional collar so as to extend in a direction parallel to the longitudinal axis of the bobbin. Respective free ends of the terminal pins of the respective rows are used to be plugged into associated holes in a printed circuit board. In view of the terminal pins of the respective rows extending parallel to the longitudinal axis of the bobbin, the transformer when the free ends of the terminal pins are plugged into the holes in the printed circuit board assumes an upright position and, hence, the transformer itself is of an upright type. In this transformer of the upright type, the insertion grooves are defined in one portion of the intermediate collar of the auxiliary bobbin region adjacent at least one of the third and fourth side faces of the bobbin, and the first and second rows of the terminal pins are provided adjacent the first and second side faces, respectively. In a modified form of the transformer of the upright type, while one of the primary and secondary windings is prepared from the winding wire having reinforced insulation, the other of the primary and secondary windings may be prepared from a normal insulated winding wire having a single insulating layer and, in such case, such one of the primary and secondary windings is passed through the insertion groove, and a portion of the intermediate collar adjacent the terminal pins for the other of the primary and secondary windings is formed with second insertion grooves for passing the other therethrough. According to a further preferred embodiment of the present invention, the bobbin having the first to fourth side faces, may have first and second collars protruding radially outwardly from respective opposite ends thereof with the intermediate collar positioned generally therebetween. The rows of the terminal pins associated respectively with the primary and secondary windings are secured to the first and second collars adjacent the first side of the bobbin, thereby rendering the transformer as a whole to be of a transverse type which, when the transformer is mounted on the printed circuit board with the free ends of the terminal pins plugged into the holes in the printed circuit board, lies generally parallel to the printed circuit board. In this case, the insertion grooves are defined in one portion of the intermediate collar adjacent at least one of the second, third and fourth side faces of the bobbin.

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