Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Reexamination Certificate
1999-09-13
2002-05-07
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
C315S407000
Reexamination Certificate
active
06384548
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a horizontal deflection circuit for use in a television display apparatus that incorporates a CRT (Cathode-ray Tube).
2. Description of the Related Art
Generally, in a video display incorporating a CRT, the raster position, which the electron beams emitted from the electron guns can reach, is displaced with respect to the screen. This is because the CRT has productive variation in raster position. As a consequence, the image displayed by the video display distorts in both vertical direction and horizontal direction, or parts of the raster fail to appear in the screen.
Most video displays, each incorporating a CRT, comprises a centering circuit that corrects the raster position. To move the raster position, a direct current is supplied to the deflection yokes. Usually the raster position can be easily corrected in the vertical direction, in view of the structure of the vertical deflection circuit. In the horizontal deflection circuit, which is usually a resonator circuit, however, it is often difficult to supply a direct current to the deflection yoke. In the television receivers, for example, the centering circuits
100
and
110
shown in
FIGS. 1 and 2
have been used hitherto. More precisely, the centering circuits shown in
FIGS. 1 and 2
are used in the horizontal deflection circuit of the so-called “diode modulator type,” which is illustrated in FIG.
3
.
The centering circuit
110
shown in
FIG. 2
can be used in ordinary horizontal deflection circuits. However, it is large in circuitry size, and its manufacturing cost is inevitably high.
The centering circuit
100
shown in
FIG. 1
can be manufactured at lower cost than any other types. However, it is not easy to incorporate the centering circuit
100
into a horizontal deflection circuit, for the following reason. As shown in
FIG. 1
, the centering circuit
100
comprises a choke coil
102
, a capacitor
103
, an S-shaped capacitor
104
, a switch
106
, and two diodes
107
and
108
. The choke coil
102
connects the capacitor
103
to a power supply
101
. The diodes
107
and
108
are selectively connected by the switch
106
to the node of the S-shaped capacitor
104
and a horizontal deflection yoke
105
.
The switch
106
may be operated, selecting the diode
108
connected to the S-shaped capacitor
104
. In this case, the diode
108
is turned on when the voltage across the S-shaped capacitor
104
falls below the voltage across the capacitor
103
. Then, the voltage across the capacitor
103
falls along the voltage across the S-shaped capacitor
104
. Hence, while the diode
108
remains on, a direct current can be supplied to the S-shaped capacitor
104
without imposing large influence on the resonance that the horizontal deflection circuit is achieving. The centering circuit
100
supplies a current equivalent to the current supplied to the S-shaped capacitor
104
, from the power supply
101
to the horizontal deflection yoke
105
, thereby moving the raster in the horizontal direction.
The switch
106
may selects the diode
107
that conducts a current in the direction opposite to the direction the diode
108
conducts a current. In this case, the diode
107
is turned on when the voltage across the S-shaped capacitor
104
rises above the potential of the capacitor
103
. Then, a current is supplied to the capacitor
103
from the S-shaped capacitor
104
, without affecting the resonance that the horizontal deflection circuit is achieving. As a result, the centering circuit
100
moves the raster in the opposite direction.
In the centering circuit
100
it is required that the average voltage of the power supply
101
be equal to the average voltage across the S-shaped capacitor
104
. It would otherwise be impossible to achieve stable horizontal movement of the raster, either to the left or to the right.
In the horizontal deflection circuit described above, the voltage across the S-shaped capacitor
104
does not much depend on the voltage of the power supply
101
in most cases. The voltage across the S-shaped capacitor
104
is often higher than the voltage of the power supply
101
. When a current flows throughout the centering circuit
100
if the diode
107
is selected to supply a current from the S-shaped capacitor
104
to the capacitor
103
, a large current is therefore supplied to the horizontal deflection yoke
105
. That is, the average voltage of the power supply
101
and the average voltage across the S-shaped capacitor
104
cannot be equal at all in the centering circuit
100
. If a large current is supplied to the horizontal deflection yoke
105
, the raster will be moved more than is necessary in the horizontal direction. In some cases, the raster position cannot be adjusted to an appropriate position.
To solve this problem, the voltage of the power supply
101
connected by the choke coil
102
to the capacitor
103
may be applied from another power supply of a higher voltage, not from the power supply that drives the deflection yoke of the horizontal deflection circuit. The use of another high voltage power supply will, however, render the centering circuit
100
too expensive to be used in ordinary television receivers.
SUMMARY OF THE INVENTION
The present invention has been made in view of the foregoing. The object of the invention is to provide an inexpensive horizontal deflection circuit that can effect a stable horizontal movement of raster.
To attain the object, a horizontal deflection circuit according to the invention has a centering circuit designed to change a direction of supplying a current to a deflection yoke, thereby to move a raster in a horizontal direction and, hence, adjust the position of the raster. The centering circuit comprises: a diode, of which cathode is connected to a node of an S-shaped capacitor and the deflection yoke; a capacitor connected at one end to the anode of the diode and at the other end to the ground; a switching element connected in parallel to the diode; and switching element control means for opening and closing the switching element, thereby to control a current flowing from the S-shaped capacitor to the capacitor and to control, ultimately, a current to be supplied to the deflection yoke.
The horizontal deflection circuit can therefore continuously adjust the raster position in the horizontal direction.
REFERENCES:
patent: 3917977 (1975-11-01), Izumisawa
patent: 3944882 (1976-03-01), Takahashi
patent: 4163179 (1979-07-01), Farina et al.
patent: 4206388 (1980-06-01), Ishigaki et al.
patent: 4242714 (1980-12-01), Yoshida et al.
patent: 4464612 (1984-08-01), Teuling
patent: 4540933 (1985-09-01), Tueling
patent: 5596249 (1997-01-01), Ochiai
patent: 2 222 058 (1990-02-01), None
patent: 94/07332 (1994-03-01), None
Patent Abstracts of Japan vol. 012, No. 106, Apr. 6, 1988, JP 62 234469.
Patent Abstracts of Japan vol. 009, No. 019, Jan. 25, 1985, JP 59 165570.
Dinh Trinh Vo
Frommer William S.
Frommer & Lawrence & Haug LLP
Sony Corporation
Wong Don
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