Electric lamp and discharge devices – Cathode ray tube – Beam deflecting means
Reexamination Certificate
1999-09-21
2001-07-17
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Beam deflecting means
C335S213000, C335S299000
Reexamination Certificate
active
06262525
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color cathode ray tube, and more particularly to a color cathode ray tube provided with a convergence device regulated to prevent convergence error caused by an external magnetic field or the like.
2. Description of the Related Art
In recent years, there has been a growing demand on the market for a color cathode ray tube which allows a user himself to correct convergence error after the color cathode ray tube is shipped, caused by an external magnetic field under working conditions.
Heretofore, correction coils mounted on the rear end of a deflection yoke disposed in front of a CPM (Convergence Purity Magnet) have been used as the major means for correcting convergence slipping of horizontal lines.
In this regard, a color cathode ray tube with a convergence device of the structure shown in
FIG. 1
has been disclosed in Japanese Patent Laid-open Publication No. 185812/96.
Color cathode ray tube unit
101
has convergence device
106
comprising deflection yoke
103
mounted on neck portion
102
, correction coil
105
wound between CPM
104
, and control circuit
107
.
Neck portion
102
of a color cathode ray tube of this kind generally has the structure shown in FIG.
2
. That is, in the inside of neck portion
102
, there is provided the triode portion comprising cathode
117
for emitting electron beams R, G, B, heater
118
for heating cathode
117
, G
1
electrode
110
, G
2
electrode
111
, and an MFL (Main Focus Lens) comprising a plurality of electrodes including G
3
electrode
112
and G
4
electrode
113
. The position for adjusting the static convergence of electron beam
115
caused by the MFL is shown as MFL position
114
. Further, on the outer circumference of neck portion
102
, correction coil
105
is disposed in the vicinity of MFL position
114
.
However, since a cathode ray tube unit of this structure is arranged so that it acts in the vicinity of the MFL to bend side beams R and B of the electron beams R, G, B, landing transition or raster rotation are caused concurrently with the convergence correction activity.
Landing transition and raster rotation are generated when a convergence correction current is supplied from control circuit
107
to correction coil
105
disposed between deflection yoke
103
and CPM
104
due to changes in orbits of electron beams caused by the magnetic field produced by correction coil
105
which affects the area up to near the deflection point of deflection yoke
103
.
Further, the amount of correction of this color cathode ray tube unit applied to correct the convergence error caused by an external magnetic field is rather insufficient. In order to meet the necessary and sufficient amount of correction, there have been no means other than augmenting the number of turns of correction coil
105
or increasing the control current supplied from control circuit
107
, both violating the policy for saving power. In other words, when the distance between correction coil
105
and phosphor screen
116
is short, it is required to augment the magnetic force of the correction coil to the side beam for correcting convergence error on phosphor screen
116
, and consequently power supply from control circuit
107
to correction coil
105
is inevitably increased.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a color cathode ray tube having a convergence device for correcting convergence error without causing landing transition or raster rotation.
Another object of the present invention is to provide a color cathode ray tube having a convergence device which is capable of performing highly sensitive correction of convergence with a reduced dissipation current.
For achieving the above purpose, the color cathode ray tube of the present invention includes a convergence device comprising a correction coil disposed between a cathode and a CPM (Convergence Purity Magnet), and a control circuit which supplies an electric current to the correction coil.
In the color cathode ray tube of the present invention, the correction coil is provided distant from a deflection yoke because the correction coil is disposed between the cathode and the CPM. Therefore, since the influence that the magnetic field generated by the correction coil due to the current from the control circuit exerts on the deflection yoke is reduced, the convergence error can be corrected without causing landing transition or raster rotation.
According to an embodiment of the present invention, the 4-pole magnet of the convergence purity magnet serves as a means for bending the side beams of the electron beams in the direction of the tube axis of the neck portion at the cathode side of the main focus lens.
Further, according to this embodiment of the present invention, the main focus lens, axis of which corresponds to axis of side beams of the electron beam in the triode portion comprising the cathode, G
1
electrode and G
2
electrode and inclined toward the tube axis of the neck portion, serves as a means for bending side beams of the electron beam toward the tube axis at the position on the cathode side of the main focus lens.
In additions, since the color cathode ray tube of the present invention disposes a correction coil away from a deflection yoke, landing characteristics and strain characteristics do not change even if a current flows in the correction coil. Also since the electron beams are corrected by means of the correction coil at a position distant from the phosphor screen, a large amount of correction can be assured on the phosphor screen, thereby reducing the current which flows from the control circuit into the correction coil.
The above and other objects, features and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings which illustrate examples of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a constitutional view showing a color cathode ray tube having a convergence device of the conventional type;
FIG. 2
is a view showing the positional relationship between the convergence device of FIG.
1
and an MFL position of an electron gun;
FIG. 3
is a schematic constitutional view of a color cathode ray tube of an embodiment of the present invention;
FIG. 4
is a constitutional view of a neck portion of the color cathode ray tube of
FIG. 3
mounted with the convergence device;
FIG. 5
is a view showing the positional relationship between the convergence device of the present invention mounted on the neck portion thereof and an MFL position of the electron gun.
REFERENCES:
patent: 4786838 (1988-11-01), Meershoek et al.
patent: 5019745 (1991-05-01), Deal et al.
patent: 5952905 (1999-09-01), Kim et al.
patent: 2235575 (1991-03-01), None
patent: 8-185812 (1996-07-01), None
Miyake Kosuke
Yamamoto Naoki
Yanai Yoshiaki
NEC Corporation
Patel Ashok
Young & Thompson
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