Cathode ray tube

Details Cathode ray tube Cathode ray tube

1998-09-22

2001-10-23

Day, Michael H. (Department: 2879)

Electric lamp and discharge devices

Cathode ray tube

Envelope

C313S450000, C313S313000

Reexamination Certificate

active

06307315

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cathode ray tube (CRT), and more particularly, to a CRT having an improved mounting structure of an electron gun in a neck portion of the CRT.
2. Description of the Related Art
FIGS. 1 and 2
show a conventional CRT using the principle of a triode. As shown, the CRT includes a bulb
10
having a screen
12
coated with a fluorescent layer
11
on its inner surface, a conductive layer
13
coated on the inner surface of portions other than a neck portion
14
of the bulb
10
, an electron gun
20
mounted in the neck portion
14
of the bulb
10
and having at least one final accelerating electrode
21
and a focusing electrode
22
, and a deflection yoke
30
mounted on a cone portion
15
of the bulb
10
. A high voltage of 25~29 kV is applied to the conductive layer
13
through an anode port
16
installed in the bulb
10
.
Referring to
FIG. 2
showing the neck portion
14
of the bulb
10
, the conductive layer
13
is connected to a spacer
24
of a shield cup
23
fixed on the final accelerating electrode
21
of the electron gun
20
so that a high voltage is applied to the final accelerating electrode
21
.
In the CRT having the aforementioned configuration, electron beams emitted from the electron gun
20
are selectively deflected by the deflection yoke
30
to excite phosphors of the fluorescent layer
11
, thereby forming an image. During this process, excess thermions removed from the electron gun
20
but not used in exciting the phosphors are emitted to the outside through the conductive layer
13
and the anode port
16
.
However, since the conductive layer
13
is not formed on the inner surface of the neck portion
14
into which the electron gun
20
is mounted, leakage current flows along the inner circumferential surface of the neck portion
14
due to the high voltage applied to the conductive layer
13
. This leakage current adversely affects an electronic lens formed between electrodes in the electron gun
20
. Further, if foreign matter is adsorbed into the inner circumferential surface of the neck portion
14
, an arc discharge may occur between the foreign matter and the electrodes due to the leakage current.
In a projector for implementing a color image by projecting a monochrome image formed at unit CRTs for red, blue and green colors, a high-brightness image is required. To this end, it is necessary to apply a high voltage to a screen coated with a conductive layer and a fluorescent layer.
However, in the conventional CRT, as described above, leakage current may flow along the inner circumferential surface of a neck portion to break insulation, thereby causing discharge on the inner surface of the neck portion and the electrodes of the electron guns. Also, since the distance between a final accelerating electrode to which a high voltage is applied and a focusing electrode is as narrow as 1~2 mm, leakage current may flow through a bead glass to cause discharge.
To overcome the above-described problem, conventionally, high-resistance layers having different resistance values are sequentially coated on the inner circumferential surface of the neck portion to be used as a final accelerating electrode. In this case, however, coating the high-resistance layers is a difficult task.
SUMMARY OF THE INVENTION
To solve the above problems, it is an objective of the present invention to provide a cathode ray tube having means for preventing leakage current due to a high voltage applied to a conductive layer from flowing along the inner circumferential surface of a neck portion.
Accordingly, to achieve the above objective, there is provided a cathode ray tube including a bulb having a screen, a conductive layer coated on the inner surface of the bulb, an electron gun mounted in the neck portion and having a final accelerating electrode electrically connected to the conductive layer, and leakage current shielding means installed in the neck portion, for shielding leakage current flowing along the inner surface of the neck portion from the conductive layer.
The leakage current shielding means includes an annular fixing portion fixed on the inner surface of the neck portion, and an inner glass having a cylindrical supporting portion spaced apart from the inner surface of the neck portion and extending axially from the fixing portion.
Also, the conductive layer is coated up to the final accelerating electrode along the inner surface of the fixing portion and supporting portion so as to be electrically connected to the final accelerating electrode.
Also, there is provided a cathode ray tube comprising: a bulb having a screen; a conductive layer coated on the inner surface of the bulb; an electron gun mounted in the neck portion and having a final accelerating electrode electrically connected to the conductive layer; and an insulator installed between the final accelerating electrode of the electron gun and the inner surface of the neck portion.


REFERENCES:
patent: 2509763 (1950-05-01), De Gier
patent: 3962599 (1976-06-01), Say
patent: 4885503 (1989-12-01), Takahashi et al.
patent: 5202606 (1993-04-01), Vrijssen et al.
patent: 5721469 (1998-02-01), Kim et al.
patent: 220857 (1942-04-01), None
Patent Abstracts of Japan, vol. 010, No. 069 (E-389), Mar. 18, 1986; JP 60 218746, Nov. 1, 1985.

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