JPS62198040A - Electromagnetic deflection yoke - Google Patents

Abstract

PURPOSE:To restrict the ringing, by reducing the combining capacity of a deflecting coil and a ferrite core extensively. CONSTITUTION:At the surface of a ferrite core for a deflection yoke, an electroconductive membrane 4 is formed, over which a spacer of an insulating coating 5, a plastic mesh, or the like is formed, and further on them, horizontal and/or vertical deflecting coils 2 and 3 are furnished. Since the conductive membrane 4 shields up the dielectric property of the ferrite core 1, the capacity is only of the surface side. Therefore, as far as the insulating coating and the like is not too large, the capacity formed in the core is prevented even though the ferrite core 1 is made of a highly dielectric constant material such as Mn-Zn type with a low resistance (10<2>OMEGA-cm or more), and the ringing can be restricted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a deflection yoke for an electromagnetic deflection type cathode ray tube (CRT).

[Prior art and its problems]

There are basically three types of deflection yokes 11 for electromagnetic deflection type cathode ray tubes (CRTs):

1) A saddle (saddle type) in which the coil is wound to form a shape similar to a saddle and placed inside the core via a bobbin. 2) The horizontal deflection coil is wound in the saddle shape of 1), and the vertical deflection coil is placed inside the core. Semi-toroidal type, which is directly wound toroidally on the outer periphery of the core.3) Slotted type, which is a type of saddle type described in 1) and has multiple grooves arranged in the radial direction around the inner surface of the core, and a coil is formed in the grooves. Among these three types, the semi-toroidal type (2) has become the mainstream deflection yoke because it has high vertical deflection efficiency and low direct current resistance.

1 and 2 show the semi-toroidal type deflection yoke of 2) above. A vertical deflection coil 2 is directly wound around a trumpet-shaped ferrite core 1 which is a combination of two halves, and a horizontal deflection coil 3 is arranged along the inner surface of the ferrite core 1.

In any of the above types of deflection yokes, when a deflection current is passed through the deflection coil, a disturbance in the horizontal deflection current, currently called ringing, occurs, which poses a problem.

In other words, it is ideal that the horizontal deflection current has a sawtooth shape as shown in Figure 3, but in reality, as shown in Figure 4, a small waveform oscillation occurs immediately after the waveform falls, and A similar oscillation occurs in the voltage proportional to its time derivative. This waveform disturbance also causes disturbance in the horizontal deflection magnetic field,
It appears as a horizontal angle change of the electron beam. On a CRT screen, this appears as a striped pattern of vertical shading near the side edges of the screen, degrading the image quality.

Although this ringing occurs with any type of deflection yoke, it is known that it occurs particularly strongly with the semi-toroidal type.

The following types of ferrite are used as the deflection yoke core.

One type is one in which the proportion of iron oxide (Fe20B) in the ferrite composition is 50 mol X or less, and is usually Mg-
Mn-Zn yarn + N1- Cu-Zn series, N1-
Zn-based ferrite belongs to this category. This type of ferrite has a low dielectric constant (10'~10'') and high resistance (
106 to 109 Ω-cIrL), it is possible to wind a coil directly on the magnetic core, and the cost is low, so it has become mainstream in consumer televisions. However, since these ferrites have a relatively large core loss, when used as a deflection yoke core for a high-definition display with a high deflection frequency, they have the disadvantage that the core generates a large amount of heat.

On the other hand, Mn is generally used as a ferrite with excellent core loss.
-Zn ferrite is known. This Mn--Zn ferrite usually has a composition in which the proportion of iron oxide is 50 mol X or more in order to further strengthen its own good magnetic properties. Therefore, it has excellent overall magnetic properties such as magnetic permeability and saturation magnetic flux density, as well as core loss, and does not cause heat generation problems even when used as a yoke core for high-definition displays. However, when the composition of not only Mn-Zn ferrite but also the above-mentioned Mg-Mn-Zn and Ni-based ferrites is iron-excessive, the crystal resistance becomes low (10
-2 to 10°Ω-cIIL), and compared to that, the intercrystalline (grain boundary) resistance is high (104 to 105Ω-crn).
The crystal becomes insulated, and the dielectric constant of ferrite becomes extremely high. (1 to 5X10') It is known that a deflection yoke using such a high dielectric constant ferrite causes much stronger ringing than a deflection yoke with a low dielectric constant.

Furthermore, since ringing tends to increase as the deflection frequency increases, the occurrence of ringing in high dielectric constant materials has become an important problem. Therefore, it is strongly desired to suppress ringing that occurs in the deflection yoke.

[Purpose of the invention]

An object of the present invention is to prevent the ringing phenomenon in an electromagnetic deflection yoke and provide a cathode ray tube (CRT) with excellent image quality.

For more specific purposes, the ferrite core of the deflection yoke is M
There is a need to suppress ringing in the case of low resistance materials such as n-Zn ferrite, and to solve this problem in semi-toroidal deflection yokes.

[Summary of the invention]

The above object of the present invention is to have a conductivity of 10 on the surface of the ferrite core for a deflection yoke (particularly at the part where the coil is wound).
It is characterized by forming a thin film of conductive material (metal, conductive paint) of 9-α or less, and placing predetermined horizontal and vertical deflection coils on top of it with spacers such as insulation coatings and plastic nets interposed. This is achieved by an electromagnetic deflection yoke.

Preferably, the ferrite core is selected from high dielectric constant types such as the Mn-Zn system. Preferably, the vertical deflection coil is of a direct-wound toroidal type, and the horizontal deflection coil is of a saddle type.

According to the present invention, the ringing phenomenon can be sufficiently prevented or suppressed, and a highly precise cathode ray tube can be provided.

The present invention will be described in detail below, but in order to facilitate understanding of the invention, the mechanism of ringing generation will be described first.

[Mechanism of ringing generation]

The deflection yoke is a component that utilizes magnetic flux leaking to the outside of the yoke, but since a coil is formed, distributed capacitance always exists between the lines. Further, since the DC resistance of the coil is small, when a certain electromotive force is applied to this coil, a resonant circuit is formed by the inductance of the coil and the capacitance between the lines, and a transient current flows. Ringing occurs when the magnetic flux due to this transient current is superimposed on the deflection magnetic flux.

At this time, there is a ferrite core adjacent to the coil, and since the l electric constant of the ferrite core is larger than the dielectric constant of air, the capacitance is increased by electrostatic coupling between the lines. If this is modeled, it will look like Figure 5.

Further, the dielectric constant of the above-mentioned low dielectric constant ferrite is 101 to 102.
In comparison, high dielectric constant ferrite has a very high dielectric constant of 1 to 5×10, so the degree of electrostatic coupling is large. As is clear from the theory of transient phenomena, as the line-to-line distributed capacitance increases, the transient current increases.

On the other hand, the electromotive force for generating ringing is given by the horizontal deflection magnetic flux crossing the vertical deflection coil. Therefore, the larger the rate of change in magnetic flux is, the larger the potential difference will be generated between the coils, and ringing will appear. When the vertical deflection coil is toroidally wound, the electromotive force generated is larger than that of a vertically wound coil due to the direction of the horizontal deflection magnetic flux and the positional relationship of the coil, and therefore the ringing is also large.

For the above reasons, it can be seen that suppressing the capacitance between the deflection coil wires has a great effect in reducing ringing.

Note that ringing was measured as follows.

[About ringing measurement method]

Since it is difficult to accurately measure the magnetic field passing through the cathode ray tube, the following method was used to measure and judge ringing.

Since there is a relative relationship between the magnetic field generated from the deflection yoke and the magnetic flux passing through the ferrite core, the horizontal deflection magnetic flux Φ within the core 1 is picked up by the pickup coil 5 as shown in FIG.

When the voltage appearing across the pickup coil 50 is viewed with an oscilloscope, it is as shown in FIG. 9, and an enlarged view of the ringing portion A is as shown in FIG. 10. Here, the maximum amplitude of ringing ■ and the initial period T are defined as ringing,
(2) The smaller T is, the smaller the ringing is.

[Detailed description of the invention]

Principle of the Invention As stated above, the present invention uses a conductive coating to suppress the occurrence of ringing. FIG. 6 is a schematic diagram showing the principle of the present invention, in which a conductive coating 4 is formed on the surface of a ferrite core 1 for a deflection yoke, an insulating coating 5 or a spacer such as a plastic net is formed on the surface, and a spacer such as a plastic net is formed on the surface. horizontal and/or
Alternatively, a vertical deflection coil 2.3 is arranged. Since the conductive film 4 shields the dielectric property of the ferrite core 1, only the capacitance on the surface side is required. Therefore, if the electric current of the spacer such as an insulating coating is not very large (for example, the number 1
0 or less), and even if the ferrite core 1 is made of a low resistance material (102Ω1 or more), for example, a high fA conductivity material such as Mn-Zn system, capacitance formation in the core is prevented and ringing is suppressed. (See Figure 6).

Embodiment FIG. 7 shows a ferrite core 1 used in an electromagnetic deflection yoke according to an embodiment of the present invention. A conductive coating 4 is formed on the inner surface and upper and lower end surfaces of the ferrite core 1, which are in contact with horizontal and vertical deflection coils 2.3 (similar to those shown in FIG. 1), and an insulating coating 5 is further formed on the surface. It is formed.

The conductive film 4 can be formed by any method. For example, AI
It is formed by vapor deposition of a metal such as ``U'' or by applying a paste containing metal particles such as A1, Cu, Ni, etc. There is no limit to its thickness. Apply and dry a resin paint that is not expensive (less than a few dozen), such as FES, epoxy, urethane, etc., and cure if necessary.The thickness of the insulating coating is several hundred microns or less.The dielectric constant of the insulating coating 5 is The lower the better, but since the conductive film 4 is present, there is no need to consider the influence of the ratio on the 18 of the ferrite core 1. Although it may be quite high, it is set to 5 or less, preferably 55 or less.

The configuration shown in Fig. 7 includes an Mn-Zn ferrite core (manufactured by TDK) with a 5 μm aluminum vapor-deposited film and an insulating coating with a dielectric constant of 3.0, and an Mn-Zn core without aluminum in the middle. ferrite cocoa, Mn-Zn ferrite cocoa without any treatment, and M without any treatment.
Ringing was measured using the g-Mn-Zn-based ferrite core D.

The results are shown in the table below. Core D was used as a standard, and other properties were determined by their ratios to core D.

Note that item 1 is ■ (relative value) and item 2 is T (relative value).
shows. Note that when observing on a cathode ray tube screen, item 1
．． 2 simultaneously exceeds t25 and 1.53, respectively, visible vertical stripes begin to appear. Therefore, sample A
has no ringing, no ringing but slightly larger items 1, 2, and C has ringing.

[Effect]

As described above, the present invention can significantly reduce the coupling capacitance between the deflection coil and the ferrite core, thereby suppressing ringing. Therefore, the electromagnetic deflection yoke of the present invention can exhibit excellent effects especially when used with a ferrite core having low resistance and high galvanicity.

As already mentioned, instead of the insulating film in the above embodiment, a spacer such as a plastic frame or net having a thickness of about 11 to 1 mm may be applied at least to the area where the vertical deflection coil is wound. .

[Brief explanation of drawings]

Fig. 1 is a rear view showing the schematic structure of a semi-toroidal yoke among conventional electromagnetic deflection yokes, and Fig. 2 is a side view showing the same yoke with a part cut away and the horizontal deflection coil omitted. Figure 3 is a graph showing the ideal current and voltage waveforms flowing through the horizontal deflection coil of the electromagnetic deflection yoke, Figure 4 is a graph showing the current and voltage waveforms with actual ringing, and Figure 5 is the graph for vertical deflection. A schematic diagram showing the state of capacitive coupling formed between the coil and the ferrite core of the yoke, No. 6
FIG. 7 is a partially cutaway side view of a ferrite core according to an embodiment of the present invention; FIG. 8 is an explanatory diagram of ringing measurement;
FIG. 9 is a graph defining ringing, and FIG. 10 is an enlarged view of the same. 1.-7 Efit Core 4-.gt8 to L and HshiLJ')shiL5..

Claims (1)

[Claims] 1. The surface of the ferrite core for the deflection yoke has a conductivity of 10Ω.
1. An electromagnetic deflection yoke, characterized in that a thin conductive film of -cm or less is formed, and predetermined horizontal and vertical deflection coils are arranged on the conductive film with a spacer interposed therebetween. 2. The electromagnetic deflection yoke according to item 1 above, wherein the conductive coating is formed at least in a region in contact with the vertical deflection coil.