Electric lamp and discharge devices: systems – Cathode ray tube circuits – Cathode-ray deflections circuits
Reexamination Certificate
1999-12-07
2001-10-23
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Cathode-ray deflections circuits
C315S380000, C315S384000, C315S387000
Reexamination Certificate
active
06307335
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a Braun tube discharge apparatus, and relates especially to a Braun tube discharge apparatus that includes a so-called spot killer function.
2. Description of the Related Art
A conventional Braun tube discharge apparatus that includes a spot killer function, such as is shown in
FIG. 5
, is disclosed in Japanese Patent Unexamined Publication No. Hei.
10-248019.
In
FIG. 5
, a vertical pulse signal, obtained by the performance of a synchronous separation operation at a one-chip IC
1
, is output via a vertical drive signal output terminal
1
a,
and is input to a vertical deflection IC
2
via a vertical trigger input terminal
2
a.
Upon receiving the vertical pulse signal, the vertical deflection IC
2
generates a saw-toothed voltage signal that it outputs via a vertical amplitude control terminal
2
b.
The saw-toothed signal is employed to drive an electron beam vertically. As for the saw-toothed signal, the side above a predetermined center potential corresponds to the scan location in the upper portion of the screen, and the side below the predetermined center potential corresponds to the scan location in the lower portion of the screen.
Upon receiving a power-OFF instruction, the one-chip IC
1
outputs a spot killer command signal via a spot killer command terminal
1
b,
and upon receiving this command signal, a spot killer circuit discharges, within a short period of time, a residual electrical charge that is held by the anode of a Braun tube. When the electrical charge that is discharged strikes the screen, the screen glows momentarily. At that time, when an impact point is fixed, an electrical charge will concentrate on that point every time the power is turned off, and a burn in the Braun tube will occur. Therefore, even when the power-OFF instruction is issued, the vertical deflection IC
2
is activated to validate the vertical drive, so that the electrical charge can be dispersed vertically when it is discharged.
However, if only the vertical drive is validated, a lightning-shaped flash of light will be displayed vertically on the screen. This may frighten a user, or the user may assume that a specific failure has occurred. Therefore, in the discharge apparatus shown in
FIG. 5
, the path between the collector and the emitter of a transistor Q
1
is rendered conductive in accordance with the output of the spot-killer command signal, and a vertical pulse signal transmission path is grounded. Then, the voltage input at the vertical trigger input terminal
2
a
goes to a low level and the scan location is moved to the lower portion of the screen. On the other hand, when the vertical pulse signal transmission path is grounded, the base voltage of a transistor Q
2
is changed, so that the path between the collector and the emitter of the transistor Q
2
is rendered conductive, and the emitter potential is drastically reduced. Accordingly, there is a drastic increase in the amplitude of a saw-toothed signal, and the length of the vertical axis of the screen is increased. That is, when the residual electrical charge is discharged from the anode of the Braun tube, the scan location is moved to the lower portion of the screen, so that it is difficult for a user to recognize it. Further, since the length of the vertical axis of the screen is increased, even when a point on the screen glows, the light-emitting point is moved outside the screen frame, and the lightning-shaped flash of light is not displayed.
According to a Braun tube discharge apparatus disclosed in Japanese Patent Unexamined Publication No. Hei. 5-191753, when the power is switched off, the screen is turned off at a constant timing in synchronism with a vertical sync signal. In this publication, it is taught that in this manner the quality for the turning off of the screen can be improved.
The following problem is encountered in the above conventional apparatuses.
Since it is presumed that the first conventional apparatus is employed for the vertical deflection IC of a vertical pulse drive type or the like, this apparatus can not be employed for a vertical deflection IC of a so-called vertical ramp drive type or the like. This is because when a vertical deflection IC of the vertical ramp drive type receives a vertical ramp drive signal, it returns part of the output as negative feedback input, performs differential amplification of the negative feedback input, and outputs the result. Even when grounding of the path for the input of the vertical ramp drive signal is synchronized with the spot killer circuit, the same effects can not be obtained.
For the second conventional apparatus, although the screen is turned off in accordance with a constant timing, the above-described arrangement can not prevent the display of a flash of light.
SUMMARY OF THE INVENTION
To resolve the above shortcomings, it is an object of the present invention to provide a Braun tube discharge apparatus that can be employed for a vertical deflection IC of the vertical ramp drive type, and that can protect a Braun tube and prevent the display of a flash of light.
To achieve the above object, according to a first aspect of the invention, there is provided a Braun tube discharge apparatus comprising: vertical ramp signal differential amplification means for receiving a vertical ramp signal to control a vertical amplitude and for returning a part of an output thereof as a negative feedback input, and for performing differential amplification of the vertical ramp signal and supplying the result to a vertical deflection coil; spot killer means for discharging a remaining electrical charge in a Braun tube when a power is turned off; and negative feedback input path voltage control means for, in synchronization with the spot killer means, dropping, to a low level, a voltage along a negative feedback input path in the vertical ramp signal differential amplification means.
According to the Braun tube discharge apparatus thus arranged, the vertical ramp signal differential amplification means receives a vertical ramp signal to control vertical amplitude, returns a part of the output as a negative feedback input, performs differential amplification of the vertical ramp signal, and outputs the resultant signal to the vertical deflection coil. When the spot killer means discharges the residual electrical charge from the Braun tube when the power is turned off, the negative feedback input path voltage control means reduces, to a low level, the voltage along the negative feedback input path of the vertical ramp signal differential amplification means. Then, the DC voltage along the negative feedback input path is drastically reduced, and the center DC value of a signal output by the vertical ramp signal differential amplification means is increased. At the same time the AC element of the negative feedback input path is lost, and the amplitude of a signal to be output is increased.
Specifically, relative to the signal output by the vertical ramp signal differential amplification means, a predetermined center DC value corresponds to the middle scan location along the vertical axis of the screen, and as the DC value is changed above or below the center DC value, the DC value corresponds to the scan location at the ends of the vertical axis. Therefore, as the center DC value is increased, the scan location is moved along the vertical axis to the bottom edge of the screen, and as the amplitude is increased, the length of the vertical axis of the screen is also increased. Therefore, it is highly probable that the position whereat the residual charge is discharged by the spot killer means will lie outside the screen frame, and even if the point whereat the residual charge is discharged should lie within the screen frame, any light-emitting point will momentarily be pushed outside the screen frame, so that a flash of light will not be displayed on the screen.
According to a second aspect of the invention, there is provided a Braun tube discharge apparatus comprising: v
Chen Shih-Chao
Funai Electric Co. Ltd.
Lackenbach Siegel Marzullo Aronson & Greenspan P.C.
Wong Don
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