GB2033669A - Flyback transformer - Google Patents

Abstract

A flyback transformer comprises a magnetic core (14,16) carrying primary and secondary windings (26, 32) the secondary winding being divided into a plurality of coil units (50, 52, 54, 56) and connected alternately in series with the same plurality of rectifying diodes (66, 68, 70, 72), the coil units being single layers wound around individual bobbins (40, 42, 44, 46), and the outermost layer bobbin (46) being provided with a support on which the plurality of diodes are fixed, whereby the whole flyback transformer obtains a compact structure. The diodes may be integrally embedded in insulation, and their support may be integral with bobbin 46. The layers may have different winding pitches. <IMAGE>

Description

SPECIFICATION Flyback transformer The present invention relates to a flybacktransformer which supplies a high voltage to a cathode ray tube of a television receiver, specifically a flyback transformer having its secondary winding formed by winding a plurality of coil units into which the sec ondary winding is divided, around individual layer bobbins and assembling the layer bobbins in a plurality of layers.

The cathode ray tubes of television receivers require in general high DC voltages of 10 to 30 kV.

This output voltage from the flybacktransformer is rectified through rectifying diodes which have a high breakdown voltage strength.

These flybacktransformers are usually designed to generate high voltages by a higher harmonictun- ing system, thus improving regulation. Recently, for tuning at a higher frequency than the fifth harmonic, the secondary winding has been divided into a plur alityofcoilunitsbya plurality of diodes to reduce the distributed capacitance of the secondary winding. In the case of such a secondary winding, each coil unit is separated to be alternatingly independent and therefore the pulse voltage generated by each coil unit is low and requires relatively lower strength for electrical insulation and a low breakdown voltage strength diode can be employed.

However, if the coil units are wound in layers with layer insulation paper or polyester film as is conventional, the secondary winding increases in diameter and the leakage inductance necessarily increases and it is thus difficult to obtain higher harmonic tuning.

On the other hand, if the number of turns per layer of the coil unit is increased using the layer insulation paper or polyester film, magnetic coupling to the primary winding increases and the leakage inductance becomes small but an insulation resin for insulation between layers is difficult to be impregnated into the layers and the insulation deteriorates accordingly from the point of view of dielectric strength.

An object of the present invention is to provide a new flyback transformer in which the leakage inductance of the secondary winding is reduced and the output voltage regulation of the secondary winding is improved.

Another object of the present invention is to provide an improved flybacktransformer in which an insulation material is fully impregnated by winding and assembling in layers the coil units of the secondary winding and the dielectric strength between coil units is improved.

According to the present invention, there is provided a flybacktransformercomprising:- a) a magnetic core; b) primary and secondary windings mounted about said magnetic core, said secondary winding including a plurality of coil units and a plurality of rectifying diodes, said coil units and said rectifying diodes being connected alternately in series; c) a coil bobbin on which said primary winding is wound; d) a plurality of layer bobbins with different diameters on which said secondary winding is wound, each of said layer bobbins being concentrically mounted in layers about said magnetic core, each of said coil units being wound in a single layer and in the same direction about each of said layer bobbins; e) means for forming a predetermined space between said layer bobbins when the layer bobbins are assembled in layers; and f) means for supporting said rectifying diodes on the outermost layer bobbin of said layer bobbins assembled in layers.

In one form of a flyback transformer constructed in accordance with the present invention, a pair of magnetic cores are combined and the primary winding wound around the coil bobbin is mounted on its legs. A plurality of terminals which are extended in the radial directions are provided in the circumferential direction on the ends of coil bobbins and have terminal pins for connecting the lead wires of the primary winding at their extreme ends. The secondary winding to be mounted on the primary winding is comprised of a plurality of coil units and a plurality of rectifying diodes which are alternately connected in series.Each coil unit is wound in a single layer around each of a plurality of layer bobbins which have different diameters, the layer bobbins are alternately fitted and assembled in layers to ensure the magnetic coupling to the primary winding and reduce the leakage inductance of the secondary winding, thus improving the regulation of output voltage of the secondary winding. A plurality of projections with the height larger than the diameter of conductor to be wound around the layer bobbin are provided in the circumferential direction at least at both ends of the layer bobbins.When the layer bobbins are assembled in layers, the extreme ends of the projections engage with the peripheral surfaces of adjacent layer bobbins whereby a space is formed between the coil unit and an adjacent layer bobbin and is filled with a sufficient amount of insulation material to increase the dielectric strength between coil units. A support means to which a plurality of rectifying diodes are to be attached is mounted on or provided with the outermost layer bobbin and the lead wires from the coil units wound around the layer bobbins are connected in sequence and the final stage diodes are connected to the high voltage lead wires.

In order that the invention may be more clearly understood, several embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which FIGURE 1 shows the connection of a flyback transformer according to the present invention, FIGURE 2 is a plan view of a flyback transformer according to the present invention, FIGURE 3 shows the cross section along the section line Ill-Ill of the flyback transformer shown in Figure 2, FIGURE 4 is a plan view of only the primary and secondary windings of the flyback transformer of the present invention, FIGURE 5 shows the cross section along the section line V-V of the flybacktransformer shown in FIGURE 4, FIGURE 6 and FIGURE 7 show another embodiment of the flyback transformer according to the invention incorporating another form of layer bobbin, and FIGURE 8 shows another embodiment of the flyback transformer of the invention incorporating another form of winding pitch of the coil unit according to the present invention, FIGURES 9 and 10 show another embodiment of the invention having alternative support means, FIGURE 11 shows a perspective view of a diode pack forming part of the embodiment of FIGURE 9 and 10.

Referring to FIGURE 1, the flyback transformer generally referenced 10 comprises a primary winding 11 which is mounted on a magnetic core 13 made of ferrite together with a secondary winding 12. The secondary winding 12 is divided into a plurality of coil units 121,123,125 and 127 which are connected alternately in series with rectifying diodes 122, 124 and 126. One end of the innermost coil unit 121 is grounded and one end ofthe coil unit 127 is connected in operation to the anode of a cathode ray tube through a rectifying diode 128 connected to the coil unit 127, thereby the total voltage rectified by the rectifying diodes 122, 124, 126 and 128 is supplied to the anode of the cathode ray tube.

FIGURES 2 and 3 show a practical construction of the flyback transformer which is connected as shown in FIGURE 1. A pair of U-shaped magnetic cores 14 and 16 are firmly clamped with a metal plate 18, clamp bolt 20 and nut 22. A cylindrical coil bobbin 24 made of synthetic plastics material is mounted on the legs of the magnetic cores 14 and 16 and primary winding 26 is wound around the coil bobbin. A plurality of terminal parts 28 extended in the radial direction are disposed with predetermined intervals in the circumferential direction on one end of the coil bobbin 24, and an end of a single terminal pin 30 is set in the extreme end of each terminal part 28, and the other end of the terminal pin 30 is projected in the axial direction of the coil bobbin 24.

Secondary winding 32 is mounted on the primary winding 26. The lead wire from the ground or earth side of the secondary winding 32 is connected to one of the terminal pins 30. The output from the high voltage side of the secondary winding, that is, the high output rectified into a DC voltage is drawn out by an anode lead wire 34 and supplied to the anode of the cathode ray tube not shown.

The primary winding 26 and the secondary winding 32 are housed in an insulation case 36 made of synthetic plastics material such as polybutyleneterephthalete reinforced with glass fibre, likewise the coil bobbin 24 and the insulation case 36 is filled up to the position shown by a broken line 38 with an insulation material such as epoxy resin or 1, 2-polybutadiene resin compound. The insulation material is omitted from the drawings for simplification of the description.

The secondary winding 32 is illustrated in detail in FIGURES 4 and 5. A plurality of coil units 50, 52,54 and 56 of the secondary winding 32 mounted on the primary winding 26 are respectively wound in a single layer on cylindrical layer bobbins 40,42,44, and 46 with different diameters. The diameters of conductors of the coil units wound on the layer bobbins is approximately 30 to 50 FL and the conductors are wound in the same direction. These layer bobbins are approximately 1 mm thick and are made of synthetic plastics material such as polycarbonate resin. The layer bobbbins can be made of a glassfibre reinforced resin as the case 36 to minimize thermal deformation of the layer bobbins.

A plurality of projections 401,402,421,422,441, 442,461 and 462 are provided at equal intervals in the circumferential direction on both end parts of the peripheries of the layer bobbins. These projections are slightly higher than the diameters of conductors of the coil units wound on the layer bobbins. The tops of these projections contact the internal peripheries of the adjacent layer bobbin. In other words, the projections 401 and 402 of the layer bobbin 40 contact the internal periphery of the bobbin 42, the projections 421 and 422 of the bobbin 42 contact the internal periphery of the bobbin 44 and the projections 441 and 442 of the bobbin 44 contact the internal periphery of the bobbin 46.Thus, small spaces are formed between the coil units 50, 52 and 54 and the internal peripheries of the layer bobbins 42,44 and &commat;pd 46 and therefore the insulation material can be filled fully and easily.

A semi-cylindrical support 48 made of the same kind of synthetic plastics material as the layer bobbins is mounted on the outermost layer bobbin 46. A small space is formed between the support 48 and the coil unit 56. Vertical walls 481 and 482 are provided on both ends of the support 48 and the termi- nals 58,60,62,63 and 64 corresponding to the coil units are provided on the tops of each vertical wall.

Lead wires 501,521,541, and 561 of the coil units 50, 52,54 and 56 are connected to terminals 58,60,62 and 64 on the vertical wall 481 and the ends of rectifying diodes 66, 68,70 and 72 are also connected to the same terminals. The terminals on the vertical wall 482 are not shown in FIGURE 4 and the terminal 63 only is shown in FIGURE 5. In other words, the other end of rectifying diode 70 is connected to the terminal 63 and the other lead wire 562 of the coil unit 56 is connected to the terminal 63.

The connection to other terminals is the same as for terminal 63. The lead wires of the coil units 50,52,54 and 56 are led out through the clearances between the projections provided on the layer bobbins 40,42, 44 and 46. The other lead wires of the coil units 50, 52 and 54 are omitted from the drawings. Parts of the vertical walls 481 and 482 are further extended outside and are used as lead wire supports 483 and 484, and a through hole 485 into which a thick anode lead wire 34 is inserted is also provided in the lead wire supports. The lead wire 34 is connected to the other end of the final stage rectifying diode 72, that is, the cathode. Accordingly, the coil units 50, 52, 54 and 56 and the rectifying diodes 66, 68,70 and 72 are connected in series as the secondary winding shown in FIGURE 1.

Hooks 486 which face radially inwardly are formed on both circumferential edges of the support 48 and engaged with the projections 461 and 462 of the layer bobbin 46 and secured on the layer bobbin 46.

Four projections 403 are formed at 90 intervals in the circumferenetial direction on an end part of the internal periphery of the innermost layer bobbin 40, while two projections 241 and 242 are formed at 1800 intervals in the circumferential direction at a position opposing the above-mentioned projection 403 on the external periphery of the coil bobbin 24 on which the primary winding 26 is wound. The extreme end of the projection 403 is interpositioned between these two projections 241 and 242.Four projections 243 at the side of terminal part 28 are formed at 900 intervals in the circumferential direction on the external periphery of the coil bobbin 24 and the extreme end of the projection 243 contacts the internal periphery of the layer bobbin and supports the layer bobbin 40 in cooperation with the projection 403 so that the layer bobbin 40 is coaxial with the coil bobbin 24.

The coil units 50,52, 54 and 56 wound around the layer bobbins 40,42,44 and 46 are divided by the rectifying diodes 66,68 and 70 and can therefore be regarded as independent coils. Accordingly, it is preferable for the coil units to provide the higher har monictuning of the same frequency, for example, the fifth harmonic tuning in conjunction with the primary winding 26 in order to supply a high DC voltage with less regulation to the anode of the cathode ray tube.

For this purpose, in FIGURE 5, the number of turns of coil of the coil units is relatively reduced from the outermost layer bobbin towards the coil unit 50 wound around the layer bobbin 40 nearest the primary winding 26, and the width of turns of the coil units 40,42,44 and 46 in the same winding pitch and direction is increased gradually so that it is the largest on the outermost coil unit 56. By this arrangement, the flybacktransformer can be designed so that the coupling factors between the primary winding 26 and the coil units 50, 52, 54 and 56 tend to be equal. Accordingly, an advantage is found to make it easy to resonate at the same frequency respective higher harmonic resonance circuits which are made with the distributed capacities including the earth capacitance of the coil units 50, 52, 54 and 56 and leakage inductances of respective coil units.

FIGURE 6 shows another form of the layer bobbin for the flyback transformer according to the present invention. The projections 741,742,761,762,781, 782,801 and 802 are provided on both ends of the layer bobbins 74,76,78 and 80 and the projections 743,763,783 and 803 are formed on the central parts. The layer bobbins can be supported to be free from deformation even though the thickness of the layer bobbins 74,76,78 and 80 is small since the projections are provided at the central parts as described above.

FIGURE 7 shows another embodiment of the layer bobbin. The projections formed at both ends of the layer bobbins here referenced 82, 84,86 and 88 are such that they are provided on the external periphery of one ends and on the internal periphery of the other ends. When using the layer bobbins and mounting the support 48 as shown in FIGURE 5 on the outermost layer bobbin 82, the hooks 486 of the support 48 should be modified in shape and the projection 401 provided on the external periphery of the innermost layer bobbin 40 shown in FIGURE 5 will be unnecessary.

FIGURE 8 shows another form of the coil unit. The widths of turns of the coil units here referenced 98, 100,102 and 104 wound around the layer bobbins here referenced 90,92,94 and 96 are equal but the winding pitch becomes larger and the number of turns becomes smaller towards the lower layers. In this case, the flyback transformer can be designed so that the coupling factor of the primary winding and the coil units does not significantly change.

In the above-mentioned embodiments, there is shown an example in which the number of turns of the coil units wound on the stacked layer bobbins vary with respective layer bobbins. The numbers of turns of the coil units wound on the layer bobbins may be equal. In this case, each coil unit is wound in an equal width, and the number of turns of one or two coils can be varied while the winding width is maintained equal. Such variation makes it difficult to ensure effective higherharmonictuningforthe banking pulse, but, even though higher harmonic tuning is not obtained, there is little leakage flux between the primary winding and the coil unit and magnetic coupling of both components is satisfactorily maintained and therefore an appropriately regulated high output voltage can be obtained from the secondary winding.

The above describes the flybacktransformer provided with four coil units but the number of coil units is not limited to four for the flyback transformers according to other embodiments. In this case, the numbers of the layer bobbins and rectifying diodes are determined in accordance with the numberof coil units.

Itis evidentthatthe layered arrangementofthe layer bobbins can be ensured by providing an engaging means such as the projections 241 and 242 of the above-mentioned coil bobbin 24 and the projection 403 of the layer bobbin 40 between the projection of each layer bobbin and the next layer bobbin.

Moreover, though the support 48 which supports the diodes is made in a semi-circularform,the hook 486 may be modified into an annular form by extending it in the circumferential direction of the layer bobbin 46.

FIGURE 9 shows an embodimentoftheflyback transformer in which the outermost layer bobbin 46 is provided with a diode supporting means. The coil unit 56 is wound on the layer bobbin 46. Expanded walls 463 and 464 are formed at both end edges of the bobbin 46 and holes 465 and 466 as many as the number of diodes are arranged in a row at the tops of walls and holes 467 and 468 for inserting anode lead wires are provided in alignment with the above-mentioned holes. Diodes 66, 68,70 and 72 are supported with the extreme ends of their lead wires inserted into corresponding holes 465 and 466 and the anode lead wires inserted into holes 467 and 468.

For such construction, a special support block 48 as shown in FIGURES 4 and 5 will not be required.

FIGURE 10 shows another embodiment of the diode supporting means. The expanded walls 463 and 464 are separated into two parts and the hooks 471,472,473 and 474 disposed opposite each other are formed at the top part. Four diodes 66,68,70 and 72 are embedded in an insulation material such as, for example, glass, epoxy resin, etc. and packed.

Both tip ends 661 and 662,681 and 682,701 and 702, and 721 and 722 of the diodes are projected in opposite directions out of the diode pack 71 as shown in FIGURE 11. The diode pack 71 is engaged with the hooks 471,472,473 and 474 of the expanded walls 463 and 464. This construction facilitates insulation and installation of the diodes.

Claims (9)

1. A flybacktransformer comprising: a) a magnetic core; b) primary and secondary windings mounted about said magnetic core, said secondary winding including a plurality of coil units and a plurality of rectifying diodes, said coil units and said rectifying diodes being connected alternately in series; c) a coil bobbin on which said primary winiding is wound; d) a plurality of layer bobbins with different diameters on which said secondary winding is wound, each of said layer bobbins being concentrically mounted in layers about said magnetic core, each of said coil units being wound in a single layer and in the same direction about each of said layer bobbins; e) means for forming a predetermined space between said layer bobbins when the layer bobbins are assembled in layers; and f) means for supporting said rectifying diodes on the outermost layer bobbin of said layer bobbins assembled in layers.

2. A flybacktransformer according to Claim 1 wherein each of said layer bobbins has a plurality of projections in the circumferential direction on both sides of the layer bobbins, thereby forming the space between said layer bobbins assembled in layers.

3. Aflybacktransformer according to Claim 1 wherein each of said coil units has substantially the same number ofturns.

4. A flybacktrnnsformer according to Claim 1 or 2 wherein the number of turns of the coil unit wound on the outermost layer bobbin is greater than the number of turns of the coil unit wound on the innermost layer bobbin.

5. Aflybacktransformer according to Claim 4 wherein the width of the turns of the coil unit of the outermost layer bobbin is substantially equal to the width of the turns of the coil unit of the innermost layer bobbin with the winding pitch of the innermost coil unit being larger than the winding pitch of the outermost coil unit.

6. A flybacktransformer according to any preceding claim wherein said means for supporting said rectifying diodes comprises a semi-cylindrical support and couplers engaged with said outermost layer bobbin.

7. A flybacktransformer according to Claim 6 wherein said support means for supporting said rectifying diodes comprises said semi-cylindrical support which includes an annular form being mounted on said outermost layer bobbin.

8. A flybacktransformer according to any of claims 1 to 5 wherein said support means for supporting said rectifying diodes comprises extended walls formed on both edges of said outermost layer bobbin of said layer bobbins assembled in layers.

9. A flyback transformer substantially as hereinbefore described with reference to FIGURES 1 to 5 orto FIGURES 6 and 7 orto FIGURE 8 orto FIGURES 9 to 11 of the accompanying drawings.