Spot killer circuit

Details Spot killer circuit Spot killer circuit

2000-06-13

2001-06-05

Wong, Don (Department: 2821)

Electric lamp and discharge devices: systems

Cathode ray tube circuits

C348S173000

Reexamination Certificate

active

06242863

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a cathode-ray tube (CRT) display system having a CRT display unit which provide displays with a CRT and other devices (a display unit other than the CRT, a video record device or the like), a video signal processing apparatus used in this CRT display system, and a spot killer circuit used in this video signal processing apparatus. More specifically, this invention relates to a CRT display system which executes a spot killer operation for neutralizing a high voltage in the CRT by flowing a current within the CRT, a video signal processing apparatus used in this CRT display system, and a spot killer circuit used in this video signal processing apparatus.
BACKGROUND OF THE INVENTION
Recently there is provided a CRT display system having a CRT display unit which provides displays with a CRT and other devices (such as a display unit other than a CRT and a video recorder) such as a television receiver incorporating a VCR therein. In the CRT display system described above, a spot killer operation is executed with a spot killer circuit to prevent spots from remaining on a screen when power is turned OFF.
In the television receiver incorporating a VCR therein, when images are recorded with a VCR while displays are being provided by the CRT, sometimes it is desired to delete a screen of the CRT without stopping the operation for recording video images. When a screen is to be deleted while recording video images, it is necessary to set only the CRT in the stand-by state when power is ON. Generally in order to set a CRT of a CRT display unit in the stand-by state when power is ON, sweeping in the horizontal or vertical direction is stopped, and generation of a high voltage in a flyback transformer as a source of a voltage for accelerating electrons within the CRT is stopped. However, there is the problem that, after the CRT is set in the stand-by state, spots remain on the screen until a high voltage in the CRT accumulated in the capacitor disappears due to discharging.
As the conventional type of CRT display system which can solve the problem described above, there is the one which executes a spot killer operation for neutralizing a high voltage in the CRT by flowing a current in the CRT using an OSD (On Screen Display) in a state where power is ON.
FIG. 5
shows general configuration of the CRT display system.
This CRT display system comprises a CRT
31
providing displays, a deflection yoke
32
which sweeps an electron beam in the CRT
31
, a sawtooth wave generation/output circuit
33
which generates a sawtooth wave for sweeping the electron beam and outputs the sawtooth wave to the deflection yoke
32
, a deflection signal processing circuit
34
which receives a horizontal/vertical synchronization signal, generates a horizontal/vertical timing pulse for generation of a sawtooth wave (sawtooth wave generation timing pulse), and outputs the sawtooth wave generation timing pulse to the sawtooth wave generation/output circuit
33
, a video signal processing circuit
35
which receives a video signal and converts the video signal to R/G/B signals, an OSD
36
which generates signals such as channel displays and executes switching between the R/G/B signals from the video signal processing circuit
35
and signals such as channel displays, a switch
37
which stops supply of the R/G/B signals, a spot killer circuit
38
which generates a pulse-like white signal based on the R/G/B signals when power is turned ON, an R/G/B output circuit
39
which receives the R/G/B signals from the spot killer circuit :
38
and drives a cathode of the CRT
31
, and a microcomputer
40
which stops supply of a sawtooth wave generation timing pulse by controlling the deflection signal processing circuit
34
, stops supply of the R/G/B signals by controlling the switch
37
, and executes a stop killer operation by controlling the OSD device
36
.
In this CRT display system, when it is required to set the CRT
31
in the stand-by state in the power OFF state, the microcomputer
40
performs following operation. That is, (1) output white on all screens with the OSD device
36
, (2) stop supply of a sawtooth wave generation timing pulse with the deflection signal processing circuit
34
, and (3) stop supply of the R/G/B signals with the switch
37
. When the operation (1) is executed, a maximum quantity of current is supplied from a cathode into the CRT
31
, and when the operation (2) is executed, generation of a high voltage in a flyback transformer is stopped. When the operation (1) is executed, the current supplied from the cathode to the CRT
31
flows neutralizing a high voltage in the CRT as a source for the current itself, thus an equilibrium being achieved in the CRT (spot killer operation). Finally when the operation (3) is executed, supply of a current from the cathode is stopped. With this operation, a voltage loaded to the CRT
31
disappears with no spot generated on a screen of the CRT
31
, and the CRT
31
is set in the stand-by state.
Further, in this CRT display system, when power is turned ON, the spot killer circuit
38
generates a one-shot pulse. Therefore, a current is supplied into the CRT
31
and flows neutralizing a high voltage in the CRT as a source for the current itself, thus an equilibrium being achieved in the CRT with generation of spots on a screen of the CRT prevented.
With the conventional technology as described above, however, the spot killer circuit
38
is used only when power is turned OFF. Therefore, when it is required to, set the CRT
31
in the stand-by state in the power ON state, a spot killer operation is executed with the OSD device
36
. Thus, when a function such as the OSD function for outputting white on all screens under control by a microcomputer is not available, it is necessary to provide a power source unit for the spot killer circuit
38
separately from and in addition to a power source unit for the circuit (for the VCR or the like) having other functions and to cut turned OFF only power for the spot killer circuit
38
. Accordingly, there occurs the problem that the circuit becomes complicated and the cost disadvantageously increases.
Further, an operation for generation of a signal for the spot killer operation is executed using the spot killer circuit
38
when power is turned OFF, and using the OSD device
36
when power is ON, which is disadvantageously redundant. Furthermore, control signals for the deflection signal processing circuit
34
, switch
37
, and OSD device
36
are different from each other, which makes the processing with a microcomputer for the spot killer operation complicated and also causes increase in size of the control program and cost.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a spot killer circuit, a video signal processing apparatus, and a CRT display system in which a power supply unit is shared by the spot killer circuit and a circuit having other functions to simplify the circuit configuration as well as to reduce the cost and the spot killer operation can be executed in the power ON state even when such functions as the OSD function are not available.
According to a spot killer circuit of one aspect of the present invention, a signal for the spot killer operation is generated when power is turned OFF, further, a signal for the spot killer operation is generated based on a control signal when power is ON. Thus, the spot killer operation can be executed using the spot killer circuit irrespective of whether power is ON or turned OFF.
According to a spot killer circuit of another aspect of the present invention, a first transistor drives a first resistor, a rectification unit generates a voltage difference between a collector and an emitter of a second transistor to accumulate electric charge in a capacitor, a switch unit grounds one edge of a third resistor based on a control signal from an external device such as a microcomputer, the third resistor pulls down a base of the second transistor when one edge of the switch unit is

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