JPH08317245A - Spot seizing prevention device - Google Patents

Abstract

PURPOSE: To avoid spot seizing more effectively by maximizing the luminance to reduce the electric charge remaining in a picture tube as much as possible at the time of turning off the power source of the picture tube. CONSTITUTION: A microcomputer 111 instructs a luminance adjustment circuit 105 to maximize the luminance just before an instruction of power-off. By the rise of the luminance of the signal, the cathode voltage outputted from an RGB output circuit 109 is minimized; and as the result, the anode current is increased and a large current flows to a picture tube 112, and the large- capacity staying electric charge is reduced. Thereafter, the microcomputer 111 turns off the power sources of the picture tube 112 and a circuit group to discharge the electric charge remaining in the picture tube. The appearance of local remaining of the spot on the fluorescent face of the picture tube is suppressed in comparison with the case that a high voltage is discharged at a time at the time of power-off, and as the result, local degradation of the fluorescent face of the picture tube is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spot burn preventing device for preventing partial deterioration of a picture tube such as a cathode ray tube of a TV or a CRT monitor.

[0002]

2. Description of the Related Art As a conventional spot burn preventing device, for example, Japanese Patent Laid-Open No. 5-207314 has been proposed.
An example of a technique for avoiding spot burning of a picture tube and preventing afterglow of the picture tube is described. JP-A-5-207314
The structure and operation of the publication will be described with reference to FIG. Figure 2
A picture tube having a high voltage power supply B +, a horizontal synchronizing circuit 202,
It includes a picture tube drive circuit 203 and a microprocessor 201 for controlling the operation mode of the receiver. The transistor TR13 responds to a turn-off command signal STBY from the microprocessor 201 to disable and control the high voltage power supply B +. The turn-off of the horizontal synchronizing circuit 202 is started at a speed. At the same time, the diode DR1
0 and DR11 respond to the turn-off command signal to supply a turn-on drive signal to at least one electron gun of the picture tube to discharge a high voltage from the picture tube.

[0003]

However, in the above-mentioned conventional configuration, the circuits for propagating the turn-on drive signal to the picture tube electron gun in response to the turn-off command signal from the microprocessor 201 by the diodes DR10 and DR11 are spot-burned. The circuit is complicated because it is added only as a countermeasure. And the cost is increased.
Also, if a dark image was displayed immediately before turning off the power of the picture tube, a considerable high voltage remained in the picture tube anode, and even with the above configuration, the screen would momentarily glow very brightly. However, there is a problem that it is difficult to completely avoid the deterioration of the picture tube.

In view of the above problems, it is an object of the present invention to avoid spot burning more effectively in addition to the function of the circuit for high voltage discharge, without having a circuit for high voltage discharge.

[0005]

In order to solve the above problems, a spot burning prevention apparatus of the present invention is a video amplifier circuit for amplifying a video signal extracted by a video detection circuit to a size required as an input of a picture tube. And a brightness adjusting circuit included in the image amplifying circuit for adjusting the brightness and a microcomputer for instructing the brightness adjusting circuit to adjust the image signal to maximize the brightness when the picture tube is turned off. The structure is adjusted so that the electric charge remaining in the picture tube is minimized.

[0006]

According to the present invention, with the above-described structure, the microcomputer receives a signal from the user or an external circuit and issues a command to turn off the power to the flyback transformer, the image amplifying circuit, and the picture tube. Sends a command to the brightness control circuit included in the image amplification circuit to maximize the brightness. By adjusting the brightness to the maximum, the anode current is increased and the large amount of electric charge accumulated in the picture tube is discharged. After that, even if the power of the picture tube is turned off, the amount of electric charge remaining is small, so that the amount of air discharge in the picture tube is small, so that deterioration of the picture tube such as spot burning can be prevented.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A spot burn preventing apparatus according to an embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 101 is a luminance signal, 102 is an image quality adjustment circuit, 1
Reference numeral 03 is a contrast adjustment circuit, 104 is a pedestal clamp circuit, 105 is a brightness adjustment circuit, 106 is an ABL circuit, 107 is a flyback transformer, 108 is a high voltage power supply, 109 is an RGB output circuit, 110 is a color difference signal, 11
1 is a microcomputer, 112 is a picture tube, 201 is a microprocessor, 202 is a horizontal synchronizing circuit, 203 is a picture tube drive circuit, DR10 and DR11 are diodes, T
R12 and TR13 represent transistors.

The operation of the spot burn preventing apparatus having the above structure will be described below. In FIG. 1, the luminance signal 101 separated from the color signal by the video amplification circuit in the previous stage enters the image quality adjustment circuit 102. The degree of adjustment is controlled by the microcomputer 111. next,
The brightness signal 101 enters the contrast adjustment circuit 103,
The brightness signal 101 is also controlled by a signal from the microcomputer 111. The DC component of the contrast-adjusted signal is reproduced by the pedestal clamp circuit 104. The pedestal clamp circuit 104 includes a brightness adjustment circuit 105.
Is added, and the brightness adjustment in this case is also controlled by a signal from the microcomputer 111. Also, A
When the anode current of the picture tube 112 increases, the BL circuit 106 controls the brightness adjusting circuit 105 to suppress the increase in brightness. The flyback transformer 107 applies a high voltage from the anode to the picture tube 112 by the high voltage power supply 108. The amplified / adjusted luminance signal enters the RGB output circuit 109, is mixed with the color difference signal 110, is amplified, and is applied to the cathode of the picture tube 112.

Now, when the power of the television receiver or the like is turned on, a large amount of electric charge is accumulated in the anode of the picture tube 112 due to the high voltage. If the power of the picture tube 112 or the above-mentioned circuit group is turned off as it is, a large amount of electric charge accumulated in the picture tube 112 is discharged at once. For this reason, electric charges may be locally concentrated on the fluorescent surface of the picture tube, and small bright spots may remain. This is called a spot residue, but when this phenomenon occurs, only a part of the fluorescent screen always shines with high brightness every time the power is turned off, so that the fluorescent screen is partially deteriorated. This is called spot burning. In order to avoid the spot remaining, it is sufficient that the high voltage is not discharged instantaneously when the power of the picture tube 112 is turned off, but can be discharged stepwise. Therefore, the microcomputer 111 commands the brightness adjustment circuit 105 to increase the brightness to the maximum immediately before commanding the power off. Since the signal brightness is increased, the cathode voltage output from the RGB output circuit 109 is minimized, and as a result, the anode current is increased, a large current is applied to the picture tube 112, and the accumulated large-capacity charges are reduced. . After that, the microcomputer 111 turns off the power of the picture tube 112 and the circuit group, and discharges the electric charge remaining in the picture tube.

[0010]

As described above, according to the spot remaining prevention device of the present invention, the large amount of electric charge accumulated in the picture tube is adjusted stepwise, that is, the brightness is adjusted to the maximum by the microcomputer before the power is turned off. By increasing the anode current to discharge the electric charge, and then turning off the power of the picture tube to discharge the electric charge remaining in the picture tube, the fluorescent screen of the picture tube is discharged rather than discharging a high voltage all at once when the power is turned off. It is possible to suppress the appearance of local residual spots, and as a result, it is possible to prevent local deterioration of the fluorescent screen of the picture tube.

[Brief description of drawings]

FIG. 1 is a block diagram of a spot burn prevention device according to an embodiment of the present invention.

FIG. 2 is a block diagram of a conventional spot burn prevention device.

[Explanation of symbols]

 101 Luminance signal 102 Image quality adjustment circuit 103 Contrast adjustment circuit 104 Pedestal clamp circuit 105 Brightness adjustment circuit 106 ABL circuit 107 Flyback transformer 108 High voltage power supply 109 RGB output circuit 110 Color difference signal 111 Microcomputer 112 Picture tube 201 Microprocessor 202 Horizontal synchronization circuit 203 Picture tube drive circuit DR10, DR11 Diode TR12, TR13 Transistor

Claims (1)

[Claims] 1. A video amplifier circuit for amplifying a video signal to a size required as an input of a picture tube, a brightness adjusting circuit for adjusting the brightness of the video signal, and a video signal for the video amplifier circuit and the brightness adjusting circuit. It is equipped with a microcomputer that commands adjustment, and when the power of the picture tube is turned off, the brightness is adjusted to the maximum and the electric charge remaining in the picture tube is minimized to prevent partial deterioration of the picture tube. A picture tube spot burn prevention device.