JPH0214178Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a core for a flyback transformer used in television receivers and various other cathode ray tube (CRT) display devices. The present invention relates to a core for a flyback transformer, which has an increased core cross-sectional area and improved ease of bobbin insertion.

A flyback transformer is also called a horizontal output transformer, and as is well known, it performs impedance matching between the horizontal output circuit and horizontal deflection yoke coil in cathode ray tube display devices, and at the same time boosts the pulse voltage generated during the retrace period of the horizontal pulse. This is a transformer used to provide the cathode ray tube's anode voltage.

The core used in this type of flyback transformer has a generally U-shaped overall shape in which two cylindrical legs 2 are connected and integrated at a central connecting part 3, as shown in FIG. Ferrite core 1,
A flyback transformer connects such core 1 to 2.
The legs 2 are assembled so that their end faces face each other, and a bobbin wound with a coil is attached to the leg 2, and the core band is fitted into the core band groove 4 formed on the outside of the core 1. It forms a structure assembled by arranging things such as wearing clothes. As shown in Fig. 1, the flyback transformer core may have both legs approximately cylindrical in shape, or may have one leg shaped like a cylinder and the other leg (not shown). Some have a structure similar to a square prism, but in any case, they are generally U-shaped. A coil winding portion is formed on the substantially cylindrical leg portion.

This coil winding section is usually made by winding a coil on a plastic bobbin, and is configured to be inserted into the cylindrical leg section of the core for the flyback transformer. It is desirable that it be as close to a perfect circle as possible. This is because if the coil bobbin is a perfect circle, the coil bobbin can be snugly inserted into the cylindrical leg portion 2. However, since it is impossible to form such a perfectly circular leg part, the conventional technology has a shape in which a fairly large cutout 5 is provided on the inner diameter part of the leg part, as shown in FIG. I had no choice but to colander.

The reason why such a fairly large missing portion 5 is necessary is due to the influence of the shape of the mold during core molding. FIG. 3 shows the state during core molding. An upper punch 7 and three lower punches (two lower side punches 8 for forming the leg portions and a lower center punch 9 for forming the central connecting portion) are required in the mold 6. Then, ferrite granules 10 containing a binder are filled between the upper punch 7 and the lower punches 8 and 9, and the core is compression-molded by a press. In this case, when considering the section AA in the figure, if a perfectly circular leg section is to be formed, a lower center punch 9 having a cross-sectional shape as shown in FIG. 4 is required. However, such a lower center punch 9 cannot be used. This is because the tip edge 9a has a shape that touches a circle, so an extremely thin mold is required, and it is difficult to manufacture a mold with such a shape. This is because even if it could be manufactured, it would be damaged immediately and cannot be used.

Therefore, as shown in Fig. 5, the tip edge 9b of the lower center punch 9 is made to have a considerable thickness, which prevents large press molding pressure and shocks from being applied during mold setting and assembly. It had become so important that it was not missing anything. In other words, if this tip edge 9b is chipped, the actual diameter of the cylindrical leg becomes so large that the coil bobbin can no longer be inserted into it. Therefore, this tip edge 9
This is because b is required to have very high mechanical strength, but since this part is elongated, it must have a thick structure. Due to manufacturing problems caused by such molds, the cylindrical leg portion 2 of the flyback transformer core has a large missing portion 5 at the inner diameter portion of the leg portion, as shown in Fig. 2. It is.

As a result, the cross-sectional area of the legs is greatly reduced, resulting in poor electromagnetic characteristics. In particular, with the recent demand for downsizing of devices, flyback transformers are no exception, and there is a strong demand for downsizing. This had become a major obstacle.

The purpose of the present invention is to eliminate the drawbacks of the prior art as described above, and to provide an improved flyback in which a coil bobbin can be easily inserted and the core has a large cross-sectional area, and therefore the core can be made smaller. Our objective is to provide cores for transformers.

The present invention, which can achieve the above-mentioned objects, is designed to improve the cross-sectional shape of the cylindrical leg of the flyback transformer core. not,
The curvature of the semicircle changes between the outside and inside, and the center positions are slightly spaced apart.

Hereinafter, the present invention will be explained in more detail based on the drawings. FIG. 6 is an explanatory diagram showing an embodiment of a core for a flyback transformer according to the present invention.
As is clear from the figure, the present invention is basically the first
This is a ferrite core 11 having an overall substantially U-shape, which is substantially the same as the conventional one as shown in the figure. Therefore, this core 11 has a structure in which two substantially cylindrical legs 12 and a central connecting part 13 connecting them are integrally molded, and the core 11 is formed on the side surface of the legs 12. A groove 4 for band attachment is provided.

Now, core 1 for flyback transformer like this
1, the present invention is significantly different from the prior art as shown in FIG. 1 in the cross-sectional shape of the leg portion 12, which is approximately cylindrical. This cross-sectional shape is shown in detail in FIG. As is clear from the figure, the cross section of this substantially cylindrical leg portion 12 has a radius of the outer half thereof.
The radius R ₁ is larger than the radius R ₂ of the inner half, and the center positions O ₁ and O ₂ are separated by a distance a. This distance a is approximately equal to the difference between the radius R ₁ of the outer half and the radius R ₂ of the inner half.

Although it is desirable that the distance a between the center positions be as small as possible, it is actually selected to be about 0.1 to 0.6 mm depending on the strength and shape of the mold. In other words, in the case of the above embodiment, the thickness equivalent to the tip of the lower center punch 9 is half the distance (a) between the center positions in FIG. /2), which is the minimum limit that can be maintained depending on the strength of the mold, specifically about 0.2 to 0.3 mm, so the value of distance a is about 0.4 to 0.6 mm. In addition, by slightly changing the mold shape, the center position
When the mold mating surface is located slightly inside O ₂ (this is more practical), the value of distance a is preferably selected to be approximately 0.1 to 0.4 mm.
The present invention differs from the prior art in that the tip edge is not very elongated and the thickness gradually changes with a radius, so even though the tip is extremely thin, it has sufficient mechanical strength. On the other hand, if the distance a between the center positions is too large, the magnetic path area of the cylindrical leg portion 12 will decrease, which is not very desirable.

When the cylindrical leg part has such a cross-sectional shape, the mold fitting part 15 is not much larger than the diameter of the leg, and the plastic bobbin can be inserted very smoothly and easily. Further, the cross-sectional area of the magnetic path can be increased by at least 0.5% compared to the conventional technology as shown in FIG. This 0.5%
Although this value seems to be a very small number, in reality, the core is being made smaller and is being used at the very limits of its characteristics, so an increase of more than 0.5% in the magnetic path cross-sectional area is a small increase in the characteristics. It is extremely effective.

The above embodiment is for a case where both legs are cylindrical in shape, but it is also effective when one is cylindrical and the other is square and a coil bobbin is inserted into the cylindrical leg. Needless to say, it can be applied. In addition, the most preferable cross-sectional shape of the cylindrical leg is when it satisfies the relational expression R ₁ = R ₂ + a, but there is no problem even if it is used at a slightly shifted position, and the distance a between the center positions is also It goes without saying that it can be changed as appropriate depending on the mold strength, shape (position of mold mating surfaces), etc.

Since the present invention is a core for a flyback transformer having the above-mentioned shape, the cross-sectional area of the cylindrical leg into which the coil bobbin is inserted can be made larger than that of the conventional one, and the cross-sectional area of the cylindrical leg part into which the coil bobbin is inserted can be made larger than that of the conventional one. Sometimes the characteristics are good and there is some margin, and if the characteristics are the same as before, it is possible to further downsize, and the coil bobbin can be inserted smoothly and easily.
The practical effects are extremely large.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing an example of a conventional core for a flyback transformer, Fig. 2 is an explanatory diagram showing a cross section of its substantially cylindrical leg, Fig. 3 is an explanatory diagram showing its molded state, and Fig. 4 is an explanatory diagram showing an impossible state of the A-A cross section, FIG. 5 is an explanatory diagram showing a possible state of the A-A cross section, and FIG. 6 is an explanatory diagram of the core for a flyback transformer according to the present invention. FIG. 7 is an explanatory diagram showing one embodiment, and FIG. 7 is an explanatory diagram showing the cross-sectional shape of the substantially cylindrical leg. 1, 11...Core for flyback transformer,
2, 12...Substantially cylindrical leg portion, _R1 ...Radius of the outer half, _R2 ...Radius of the inner half, a...Distance between center positions.

Claims (1)

[Scope of utility model registration request] In a core for a flyback transformer that has a generally U-shaped overall shape and at least one leg of which is approximately cylindrical, the cross section of the cylindrical leg is such that the radius of its outer half is greater than the radius of its inner half. A core for a flyback transformer, characterized in that the cores are large in diameter and their centers are spaced apart by the same amount as the difference in their radii.