KR100274516B1 - Magnetic focusing device for cathode ray tube - Google Patents

Abstract

The magnetic focusing device of the present invention is disposed around the neck 8 of the cathode ray tube 1. The magnetic focusing device includes a magnetic frame having a gap 13 in a portion radially closest to the neck 8; A static focusing coil (11) housed in the frame and energized by a direct current; A dynamic focusing coil 12 is disposed between the static focusing coil 11 and the neck 8 of the cathode ray tube and is energized by a periodically changing current. The magnetic focusing device is characterized by a magnetic frame composed of frame members 20 and 21 having different permeability, and the dynamic focusing coil 12 is made of a material having a lowest permeability and disposed in the vicinity of the gap 13. It is characterized by using a frame member as a magnetic frame.

Description

Magnetic focusing device for cathode ray tube

1 is a partial cross-sectional perspective view of a cathode ray tube having a magnetic focusing device according to the present invention.

2 (a) and 2 (b) are longitudinal cross-sectional views cut along the main axis Z of the cathode ray tube of the conventional magnetic focusing apparatus, respectively.

3 (a) and 3 (b) are diagrams showing the distribution along the main axis Z of the focused magnetic field generated by the magnetic focusing apparatus of FIGS. 2 (a) and 2 (b), respectively.

4 (a) to 4 (d) are the longitudinal cross-sections cut along the main axis Z of the magnetic focusing device according to the present invention, and the distribution along the main axis Z of the focusing magnetic field generated by these magnetic focusing devices. Drawing.

FIG. 5 is a perspective view showing a portion of the magnetic focusing device of FIG. 4 (a).

6 shows the change in the real and imaginary components of the complex permeability of ferrite compressed to high temperature as a function of operating frequency.

* Explanation of symbols for main parts of the drawings

1: cathode ray tube 8: neck of cathode ray tube

10 magnetic frame 11: static focusing coil

12: dynamic focusing coil 13: gap

20, 21, 22: magnetic frame member

H: magnetic field generated by the static focusing coil 11

h: magnetic field generated by the dynamic focusing coil 12

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cathode ray tube having an electron gun and a magnetic focusing device for focusing an electron beam radiated from the electron gun by magnetism.

A magnetic focusing device is usually used with a high resolution cathode ray tube. Since such a magnetic focusing device generates a magnetic field coaxial with the electron beam radiated from the electron gun, the electron beam can be made as small as desired when the electron beam collides on the screen of the cathode ray tube.

Such cathode ray tubes are used in the field of, for example, projection type televisions having high resolution or professional display devices. The focusing lens formed by the magnetic focusing device can be realized by an annular winding housed in a permanent magnet means or a magnetic frame with a gap through which an adjustable direct current flows.

It is sometimes necessary to add a dynamic focusing coil to the main focusing coil in order to focus the electron beam over the entire surface of the screen of the cathode ray tube with the same accuracy. In that case, the magnetic field formed by the dynamic focusing coil modulates the magnetic field of the main focusing coil in accordance with the position of the collision point of the electron beam on the screen. The frequency of the current flowing into the auxiliary coil is the same as the prescan frequency of the screen. As a result, at high scan frequencies, for example, 16 KHz or higher scan frequencies,

(1) a strong electrical coupling is generated between the static focusing coil and the dynamic focusing coil,

(2) a strong current is induced by the dynamic focusing coil in the frame of the magnetic frame including the static focusing coil, resulting in a loss of energy,

(3) The magnetic drag occurs due to the time required for the formation of a magnetic field in the magnetic frame, which is a problem at high scanning frequencies.

(4) There are certain problems, including the problem that the action of the dynamic magnetic field acting on the electron beam is weakened as the scanning frequency is increased.

It is an object of the present invention to provide a magnetic focusing device for a cathode ray tube having a dynamic focusing coil operating at a prescan frequency of 16 KHz or higher. This magnetic focusing device is a device which prevents defects such as magnetic drag, coupling between the static focusing coil and the dynamic focusing coil, electrical loss and magnetic loss from reaching a problematic value.

The magnetic focusing device according to the present invention includes a static focusing coil configured to pass a direct current and a dynamic focusing coil configured to pass a variable periodic current. This magnetic focusing apparatus includes a magnetic frame composed of members having different permeability.

The focal length f of the magnetic focusing lens is given by the following equation (1).

[Equation 1]

In Equation 1, H (Z) is a magnetic field generated along the main axis Z of the cathode ray tube, and k is a coefficient determined by the geometry of the magnetic focusing device. If the magnetic field H (z) is modulated by a magnetic field that changes in time, a so-called operating magnetic field h (z), Equation 1 may be represented by Equation 2 or Equation 3 below.

[Equation 2]

[Equation 3]

In principle, in order to reduce energy consumption, it is desirable to modulate the static magnetic field H (z) with the smallest dynamic magnetic field h (z). With regard to this point, if the h "H, h ² (z), wherein the dz is so negligible with respect to the other two, wherein the variation in focal length which is induced by modulation of the magnetic field H is formula of the following 4 Can be provided by

[Equation 4]

From this, it can be seen that the dynamic focusing coil can operate more effectively when the action regions of the magnetic fields H and h along the main axis Z overlap.

1 shows a cathode ray tube 1, which deflects an electron beam 5 emitted from an electron gun 4, and impinges the collision point of the electron beam 5 on the screen 7 of the cathode ray tube. 6) is provided with a deflection device 2 for scanning the front surface of the screen. The cathode ray tube further comprises a magnetic focusing device 3 for the electron beam, which is arranged between the deflector 2 on the neck 8 of the cathode ray tube and the electron gun 4. have.

In the embodiment of the magnetic focusing apparatus 3 according to the prior art shown in FIGS. 2 (a) and 3 (a), the static focusing coil (not shown) is arranged on the neck 8 of the cathode ray tube 1. 11 is accommodated in the magnetic frame 10 opened in the gap 13 in which the static magnetic field H appears. The dynamic focusing coil 12 is arranged at the level position of the gap so that the dynamic magnetic field h and the static magnetic field H formed thereby act at the same position on the main axis Z and optimize the action of the magnetic field h. It is. The magnetic frame 10 is usually made of soft iron, i.e., a material having a weak residual magnetic field, which is an important characteristic for causing the magnetic lens formed by the magnetic field H to perform the same function every time the magnetic focusing device is operated. But. The magnetic focusing apparatus of FIG. 2 (a) has the following limitations.

(1) The magnetic field h generated by the dynamic focusing coil 12 is accommodated in the magnetic frame 10. Therefore, electrical coupling is generated between the static focusing coil 11 and the dynamic focusing coil 12, in particular, changing the amplitude of the magnetic field H in time.

(2) The electric current induced by the dynamic focusing coil 12 in the magnetic frame 10 made of soft iron becomes large, and since the resistance of the soft iron is small as about 10 占 // cm, very large energy loss occurs. In this respect, a resistance of at least 1 Ω / cm is preferred to the extent that electrical losses are negligible.

Another solution by the prior art is shown in Figures 2 (b) and 3 (b), in which the dynamic focusing coil 12 acts on the magnetic field H and h along the main axis Z. The position is offset from the gap 13 in such a manner that the overlap of the regions is made small. The mu-metal member 14 of several tens of millimeters in thickness magnetically insulates the dynamic focusing coil 12 from the magnetic frame 10, thereby providing dynamic dynamics with the static focusing coil 11. The coupling between the focusing coils 12 becomes very weak. The position of the dynamic focusing coil 12 is less sensitive to the magnetic field H than in the case described in FIG. 2 (a). Therefore, if the same modulation is provided for H, it is necessary to increase the value of the current of the dynamic focusing coil 12, and thus supply of high energy that is unacceptable in high frequency operation is essential. In addition, the loss due to Foucault current (eddy current) is still very high because the resistance of the muu metal (about 50μΩ / cm) is low.

In addition, the prior art magnetic focusing device has a problem of magnetic drag generated by a time shift between a current flowing through the dynamic focusing coil 12 and a magnetic field generated by the current. have. With this magnetic drag, the focus is asymmetrical between both ends of the same line. This time shift occurs because the dynamic action of the material of which the magnetic field h is closed, soft iron in the first example, and muew metal in the second example is not good. Therefore, in the magnetic focusing apparatus shown in FIG. 2 (b), the time required for the magnetic field to be 99.9% of the set value necessary for substantially reducing the magnetic drag is about 20 microseconds.

The magnetic focusing apparatus of FIG. 4 (a) is a cross-sectional view illustrating an embodiment of the present invention, and FIG. 4 (c) shows the distribution along the main axis Z of the focusing magnetic field generated by the magnetic focusing apparatus. FIG. 4 is a perspective view partially cut out of the magnetic focusing device of FIG. In this embodiment, the magnetic field H of the static focusing coil 11 and the magnetic field h of the dynamic focusing coil 12 have a working area which is changed along the main axis Z of the cathode ray tube. The two coils are arranged such that most of the working region of the magnetic field h generated by the dynamic focusing coil is located in the working region of the magnetic field H generated by the static focusing coil. Thus, the dynamic focusing coil 12 is It is arranged in the vicinity of the gap 13 formed by blocking the magnetic frame constituting the substantially annular frame surrounding the static focusing coil 11. This configuration is possible and efficient, in particular, by constructing the frame with two members 20, 21 composed of materials having different permeability at frequencies of 16 KHz or higher.

In general, the permeability of the material is usually constant up to a certain frequency at which the skin effect can be detected. In order to show the action related to the frequency of this material, it is common to treat the permeability as a complex function represented by the following equation (5).

[Equation 5]

In this equation, μ 'is a function of frequency that characterizes the magnetization of the material, and μ ″ is another function of frequency that characterizes magnetic losses inside the material.

According to experience. It was found that when a soft iron was used to manufacture the frame member 21 and ferrite was used to manufacture the other member 20 of the frame, a good effect was obtained. These two frame members 20, 21 are disposed on both sides of the gap 13, respectively. To facilitate fabrication and assembly, the ferrite member 20 is a crown-shaped form that forms the wall portion of the frame surrounding the static focusing coil 11, ie the wall portion perpendicular to the axis Z of the cathode ray tube. Has At the same time, the dynamic focusing coil 12 is disposed underneath the ferrite member closest to the neck of the cathode ray tube so as to affect the electron beam for optimal action with minimal current. In this way, the magnetic field generated by the dynamic focusing coil 12 is almost contained in the ferrite member 20. There is no presence in the soft iron member. As a result, the coupling between the static focusing coil 11 and the dynamic focusing coil 12 is very weak.

The results of the analysis of the action related to the frequency of ferrite are shown in FIG. 6, which shows that the permeability component μ 'maintains a high value (about 2000) up to a frequency of around 1 MHz, The value of the imaginary part μ "due to the loss is kept at a low value up to a frequency close to 200 KHz. In this case, the time required for the magnetic field to be 99.9% of the set value necessary to substantially reduce the magnetic drag. Because of the size of microseconds, the phenomenon of magnetic drag is very weak, and finally, since the resistance of the ferrite is about 100? / Cm, the loss due to the current induced in the ferrite remains small.

Ferrite used as the material of the frame member 20 is product number T22 manufactured by LCC-Cie Europeenne de Composants Electroniques.

In another embodiment of the invention shown in FIGS. 4 (b) and 4 (d), the ferrite member 22 is disposed at the static focusing coil 11 closest to the neck 8 of the cathode ray tube. It forms the wall part of the magnetic frame which surrounds. The ferrite member 22 in this embodiment takes the form of a cylindrical tube whose horizontal axis coincides with the main axis Z of the cathode ray tube. As in the case of FIG. 4 (a) described above, the dynamic focusing coil 12 is disposed close to both the neck 8 of the cathode ray tube and the edge of the gap 13 on the lower side of the ferrite member.

Claims (11)

A magnetic focusing device arranged around a neck (8) of a cathode ray tube (1), comprising: a magnetic frame having a gap (13) in a portion radially closest to the neck (8); A static focusing coil (11) housed in the magnetic frame and energized by a direct current; A magnetic focusing device comprising a dynamic focusing coil (12) disposed between the static focusing coil (11) and the neck (8) of the cathode ray tube (1) and energized by a periodically changing current, wherein the magnetic The frame is characterized in that the magnetic focusing device is composed of frame members (20, 21) different from each other. 2. The magnetic focusing apparatus according to claim 1, wherein the frame members (20, 21) having different permeability are arranged at both sides of the gap (13), respectively. 2. The magnetic focusing device according to claim 1, wherein the dynamic focusing coil (12) is arranged close to the gap (13) of the frame members (20, 21) surrounding the static focusing coil (11). . 2. The magnetic focusing device according to claim 1, wherein the magnetic field (h) generated by the dynamic focusing coil (12) uses a frame member formed of a material having the lowest permeability as a magnetic frame. 5. The frame member (20) made of the material having the lowest permeability is in the form of a crown which is received in a plane centered on the Z axis of the cathode ray tube (1) and perpendicular to the Z axis. Magnetic focusing device. 5. The magnetic focusing apparatus according to claim 4, wherein the frame member (20) made of the material having the lowest permeability is in the form of a cylindrical tube whose horizontal axis coincides with the Z axis of the cathode ray tube. The magnetic focusing apparatus according to claim 1, wherein the materials forming the frame member (21, 20) are soft iron and ferrite, respectively. 5. The magnetic focus device of claim 4, wherein the material having the lowest permeability has a resistance of at least about 1 Ω / cm. The magnetic focusing apparatus according to claim 1, wherein the magnetic focusing apparatus is constituted by a combination with the cathode ray tube (1). A magnetic focusing device arranged around a neck (8) of a cathode ray tube (1) having a main axis (Z), comprising: a magnetic frame having a gap (13) in a portion radially closest to the neck (8); A static focusing coil (11) housed in the magnetic frame and energized by a direct current; Magnetically provided with a dynamic focusing coil 12 disposed adjacent the static focusing coil 11 around the neck 8 of the cathode ray tube 1 and energized by a variable current of about 16 KHz or longer period. In the focusing device, the first working region along the main axis Z of the cathode ray tube 1 of the first magnetic field h generated by the dynamic focusing coil 12 is connected to the static focusing coil 11. A magnetic focusing device, characterized in that it is biased with respect to the second working region of the second magnetic field (H) generated by it, but most of it is retained within the second working region. 11. A magnetic focusing device according to claim 10, wherein said magnetic focusing device is constituted by a combination with said cathode ray tube (1).