JPS6243302B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electron gun that emits a plurality of electron beams, and more particularly to a structure of an electron gun that can focus the electron beams on a target with extremely high precision. For example, in a normal color picture tube equipped with an electron gun that emits a plurality of electron beams, each of the electron beams passes through a respective electron lens and is deposited on the inner surface of the face plate of the color picture tube. The light is focused on a predetermined phosphor layer of a target consisting of dot-shaped or band-shaped phosphor layers that emit red, green, and blue colors.
In this case, the electron lens is generally formed by an electrostatic field, and the electron beam is focused while passing through the electrostatic field. The electrostatic field is formed between at least two opposing electrodes that are arranged perpendicular to the path of the electron beam and have an aperture through which the electron beam passes, and the characteristics of the electron lens created by this electrostatic field are normal. It can be changed depending on the voltage and distance applied between the opposing electrodes, the size of the aperture through which the electron beam passes, etc. In addition, it is said that the performance of an electron gun is better as the magnification and spherical aberration of the electron lens are smaller. Therefore, it is necessary to use an electron lens with a long focal length, but the most effective method is to use a voltage between electrodes. In general, the stem pins installed in the base of the color picture tube must be within a range that does not cause mutual discharge, and the dimensions of the aperture through which the electron beam passes must be such that the inner diameter of the neck of the color picture tube is Since it is constrained by other electrical conditions, it is not possible to design it arbitrarily large, and furthermore, increasing the distance between the opposing electrodes will reduce the stray electric field generated on the inner wall of the network and the This is also unsuitable since the properties of the electron lens are affected by the undesired electric field of the electron lens. In any case, the design of the electronic lens is constrained by the physical conditions determined by the design of the color picture tube. This is especially true in the case of color picture tubes, which require multiple electron beams, so the above-mentioned limitations are particularly severe. A general trend to circumvent the various constraints mentioned above is to combine electrode voltages and electrode numbers within permissible ranges to create long focal length electron lenses. For example, JP-A-51-76072
An example of this is the electron gun described in Japanese Patent Laid-Open No. 51-77061. As seen in these examples, methods of combining electrode voltages and types of electrodes generally complicate the structure of the electron gun, or require additional voltages to be applied in order to form an electron lens. , which usually impairs economic efficiency. Generally, in order to improve the performance of an electronic lens, the voltage to be applied must be increased, including the example mentioned above. In order to ensure the reliability of a television receiver equipped with a picture tube, special measures must be taken, which further reduces economic efficiency. In order to overcome the above-mentioned drawbacks, the inventor first applied for an electron gun whose electron lens was designed to focus at a high voltage, but the voltage externally applied to the color picture tube was lower than that. Next, Figure 1 a, b, Figure 2 and 3
The structure and equivalent circuit will be explained with reference to figures. The basic type of the electron gun shown in the figure is a well-known unipontential in-line electron gun, and the electron gun 1 consists of a plurality of electrodes and a plurality of glass support rods 10 that support them. The electrodes are three cathodes 2, 3, 4, a first grid 5, a second grid 6, a first or third focusing grid 7.
A second or fourth focusing grid 8 and a second or fifth focusing grid 9 are attached to the glass rod 10 in this order. the three cathodes 2;
Reference numerals 3 and 4 emit electron beams along the paths of three beams on the same plane, and the first grid 5 and the second grid 6 are flat electrodes arranged close to each other, each aligned with each electron beam path. The third grid 2 has three openings arranged close to the second grid 6 and has two cups 2 joined at their open ends.
0 and 21, and the closed ends of the cups 21 and 21 have three holes aligned with each electron beam path, respectively.
Electron beam apertures are provided. Openings 17, 18, 1 of the first cup 20
9 has a larger diameter than the opening of the second grid 6, and the openings 22, 23, 24 of the second cup 21 have a diameter larger than that of the opening of the second grid 6.
The opening of the cup 20 is larger than that of the cup 20 shown in FIG. Further, the fourth grid 8 is made up of at least three auxiliary electrodes, the first electrode 25 and the second electrode 27 are each made up of two cup-shaped electrodes joined together, and each of the three auxiliary electrodes is aligned with each electron beam path. An opening is provided. This first electrode 25 and the second
The electrodes 27 are electrically connected and have the same potential. The first electrode 25 and the second electrode 27 are spaced apart from each other in the electron beam path direction, and a third plate-shaped electrode 26 (hereinafter simply a third
) is arranged, and this third electrode 26
There are also three apertures aligned with each electron beam path. The fifth grid 9 is the third grid
7 and the fourth grid 8 by a distance approximately equal to the distance between the fourth grid 8 and the fourth grid 8 ;
At least 3 electron beams aligned with each of the 3 electron beam paths
It consists of a cup-shaped electrode provided with apertures. The three openings 36 of this fifth grid 9,
Among the holes 37 and 38, the central opening 37 is aligned with the openings from the first grid 5 to the fourth grid 8 , but the openings 36 and 38 on both sides are outside the central opening 37, respectively. It is slightly deviated towards the other side. Further attached to the fifth grid 9 is a converge escape cap 42 having a bottomed cylindrical shape and having three openings at its bottom substantially aligned with each electron beam path. A valve spacer 45 made of three metal strips projecting outward is attached to the open end of the converge encup 42. In the electron gun having such a structure, the third grid 7 and the fifth grid 9 are connected, an anode voltage is applied through the valve spacer 45, and the fourth grid is connected to the third grid 7 and the fifth grid 9.
Connecting the first electrode 25 and second electrode 27 of 8 ,
Especially considering the case where no voltage is applied and the third electrode 26 is grounded, for example, the first electrode 25,
The second electrode 27 has a distance G 1 between the facing surfaces of the third grid 7 and the first electrode 25 and a distance G ₁ between the facing surfaces of the first electrode 25 and the third electrode 26.
G ₂ and capacitors C ₁ and C ₂ approximately determined by
The potential generated by this will be applied as a focusing voltage. In this case, the third electrode 26 is preferably designed so as not to significantly influence the focusing voltage of the electron gun. That is, a voltage of 0 volts is applied to the third electrode 26, E=25 KV is applied to the anodes, that is, the third grid 7 and the fifth grid 9, and the voltage of the first electrode 25 and the second electrode 27 of the fourth grid 8 is applied. If e ² is 9KV,
As is clear from the equivalent circuit in Figure 3, G ₁ /G ₂
= 1/0.6, but
Here, the gap ratio of G ₁ /G ₂ changes depending on the shape of the opposing part of each electrode, so generally speaking, G ₁ /G ₂ =
It is not 1/0.6. In other words, the electron gun having the above-mentioned structure is excellent in that it has the desired performance as the electron gun mentioned above despite the low voltage applied from the outside, but the focusing electrode, i.e. First electrode 25
and that the potential of the second electrode 27 is unstable;
That is, there is a drawback that the voltages to be applied to the first electrode 25 and the second electrode 27 at the start of operation of the color picture tube and after long-time operation are likely to change. The present invention has been made in view of the above drawbacks, and
The present invention relates to a structure of an electron gun that eliminates the problems of the previous application and can obtain a constant focused voltage from the start of operation of a color picture tube until after a long period of operation. Next, one embodiment of the present invention will be explained with reference to FIG. In the figure, the same reference numerals as those in the previous application indicate the same parts, and no particular explanation will be given. i.e. the first focusing grid, i.e. the third grid 7.
and the third focusing grid, that is, the fifth grid 9, are connected and an anode voltage is applied, and the fourth grid 8
The first electrode 25 and the second electrode 27 are connected to each other, and no voltage is applied to the third electrode 26 inserted between the first electrode 25 and the second electrode 27. is connected to an external low voltage power supply or ground voltage. Shield structures 46 and 47 are protruded from the peripheral edges of the third grid 7 and the fifth grid 9 so as to substantially cover the side surfaces of the first electrode 25 and second electrode 27, respectively. A feature of the embodiment of the present invention having the above-described structure is that the first electrode 25 and the second electrode 27 are not particularly connected to a power source and are in a so-called "floating" state. By the capacitor formed between the third electrode 26 of the third grid 7 and the fifth grid 9, which are arranged opposite to the electrodes 25 and 27, respectively,
Since the potential is determined, the two electrodes 2
When the potentials of the structures around the electrodes 5 and 27 change, the potentials of the first electrode 25 and the second electrode 27 change accordingly, ie, become unstable.
In particular, as shown in the figure, the electron gun of a color picture tube is generally housed in a thin neck portion 48 of the color picture tube, and therefore is susceptible to the influence of the potential on the inner surface of this neck portion 48. For example, as shown in the figure, the network part 48
A conductive film 49 is coated on the inner surface, and due to the influence of this conductive film 49, the first electrode 25 and the second electrode
The potential on the inner surface of the network portion 48 near the second focusing electrode consisting of the electrode 27 increases. The rise in potential on the inner surface of the network portion 48 stabilizes after a certain period of time, but the time it takes to stabilize varies depending on the shape of the color picture tube and other factors, and generally takes 10 minutes or more than 30 minutes. Sometimes it takes time. That is, in the electron gun of the prior application, when the potential on the inner surface of the network portion 48 rises, the amount of charge accumulated in the capacitors C ₁ and C ₂ changes in the equivalent circuit shown in FIG. 3. However, by providing the shield structures 46 and 47 as in the electron gun of the present invention, the applied voltage differs from the applied voltage calculated using the equivalent circuit described above, so that the applied voltage is different from that calculated using the equivalent circuit. Changes in the potential on the inner surface of the first electrode 2
5 and the second electrode 27 are not received. As described above, the shield structures 46 and 4 are installed so as to substantially cover the side surfaces of the first electrode 25 and the second electrode 27.
By providing 7, there is no influence of potential changes on the inner surface of the network portion 48, and even at the start of operation of the color picture tube and after a long period of operation, the potential change applied to the first electrode 25 and the second electrode 27 is completely eliminated. We were able to obtain an electron gun with extremely good focusing characteristics because the potential was always constant. In the above embodiment, the shield structure is extended from the third grid 7 and the fifth grid 9 , but this is because the first electrode 25 and the second electrode It goes without saying that even if the shield structure is formed so as to substantially cover the side wall portion of 27, the same effect as in the embodiment described above can be obtained.

[Brief explanation of the drawing]

Figure 1 is a side view and plan view of the electron gun of the earlier application, Figure 2 is a sectional view of Figure 1, Figure 3 is an equivalent circuit for explaining the principle of the main parts of Figure 2, and Figure 4. 1 is a sectional view showing an embodiment of the electron gun of the present invention and a neck portion. 1 ... Electron gun, 2, 3, 4... Cathode, 5... First grid, 6... Second grid, 7 ... Third grid (first focusing electrode), 8 ... Fourth grid (first focusing electrode). 2 focusing electrode), 9... Fifth grid (third focusing electrode), 46, 47... Shield structure, 48...
Network portion, 49... conductive film.

Claims (1)

[Scope of Claims] 1 At least a third grid, a fourth grid, and a fifth grid, wherein the fourth grid is provided opposite to the third grid and the fifth grid, respectively, and electrically connected to each other. It consists of a first electrode, a second electrode, and a third electrode inserted between the first electrode and the second electrode, and the third grid, the first electrode, the third electrode, and the second electrode. In the electron gun, a potential is applied to the first electrode and the second electrode via capacitors formed between the electrode and the fifth grid, respectively.
An electron gun characterized in that a shield structure is disposed to substantially cover side surfaces of the electrode and the second electrode. 2. The electron gun according to claim 1, wherein the shield structure is formed to protrude from the peripheral edges of the third grid and the fifth grid. 3. The electron gun according to claim 1, wherein the shield structure is formed to protrude from the peripheral edge of the third electrode in the direction of the third grid and the fifth grid.