JPH0863124A - Circuit for preventing burning of display screen - Google Patents

Abstract

PURPOSE: To prevent burning of a display screen by reducing brightness of a picture by the prescribed ratio when the same picture is continued more than the prescribed hours, in a PDP display device. CONSTITUTION: This circuit is constituted with a comparator 3 in which average video level data Dn is compared with average video level data one field before average video data Dn, when they are not coincident, the prescribed data d1 is outputted, a flip flop 4 in which the average video level data Dn and the d1 are inputted, the present output is held in a period in which the d1 is not inputted, when the d1 is inputted, the present output is updated to inputted average video level data, and it is fed back to the comparator, a counter 5 which counts a signal of a vertical period making the data d1 as a rest signal, and a control section 6 which controls a video signal processing section 7 so that the data d1 and count data from the counter are inputted, when the d1 is not inputted until the count data reaches the prescribed limit value, brightness of video is reduced to the prescribed brightness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display surface burn-in prevention circuit, and more particularly, it is mainly suitable for a PDP (plasma display panel), and when the same screen continues for a predetermined time or longer, the brightness of the image is increased. The present invention relates to a circuit in which the burn-in of the display surface is prevented by reducing a predetermined ratio.

[0002]

2. Description of the Related Art In a video display device using a PDP, if the same video is displayed for a long time without limiting to a highlight image, the PDP
Image sticking or heat generation occurs on the display surface. On the other hand, PDP
In general, the conventional image display device using the above has only a function as a display terminal, and therefore, the fact is that no measures have been taken against burn-in of the display surface. As one method of preventing the image sticking, a method of increasing the image sticking preventive measure by software on the signal sending side can be considered, but this is not an essential solution.

[0003]

Therefore, under the circumstances where it is expected that the video display device using the PDP will be more and more widely used for the display of Nintendo, teletext, etc., in view of the image sticking on the display side of the device. It is required to deal with. The present invention has been made from this point of view, and when the same image continues for a certain period of time or more, it is possible to prevent image sticking on the display surface by automatically reducing the brightness of the screen. The purpose is to provide a protection circuit.

[0004]

According to the present invention, the current average video level data is compared with the average video level data one field before the current average video level data. , A latch circuit for outputting the average video level data one field before based on the current average video level data and the predetermined data from the comparator, and the predetermined data output from the comparator As a signal, a counter that counts a signal of a vertical cycle, predetermined data output from the comparator and count data from the counter are input, and the predetermined data is supplied to the predetermined predetermined value by the time the count data reaches a predetermined limit value. When there is no data input, the video signal is There is provided a display surface seizure prevention circuit constituted by a control unit for controlling the processing unit.

[0005]

The average video level data of the current input video signal (current average video level data) is constantly compared with the average video level data of one field before the current time, and when the current average video level changes, a predetermined value is determined. The data of is output (comparator). The average video level data one field before the current average video level data is fed back from the flip-flop. In the above comparison, a state in which the predetermined data is not output from the comparator for a predetermined time, that is,
When there is no change in the average video level for a predetermined time, the control unit controls the video processing unit to reduce the brightness or contrast of the video, or both. The predetermined time is managed by counting vertical cycle signals with a counter.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A display surface burn-in prevention circuit according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of essential parts showing an embodiment of a display surface burn-in prevention circuit according to the present invention.
In FIG. 1, 1 is an A / D converter for converting an analog video signal into a digital video signal, and 2 is an average video level (hereinafter referred to as "APL") detected from the digital video signal and outputs APL data Dn. APL detection unit 3, 3 is the current input APL data Dn (current average video level data)
And the APL data one field before the same Dn in time are compared, and when both data do not match, the predetermined data
A comparator 4 that outputs d1 is a flip-flop that serves as a latch circuit that outputs the APL data one field before, which serves as a reference for comparison in the comparator 3, and a reset 5 (clear (CLR )] A counter for counting the signal of the vertical cycle while being controlled, 6 is a control unit for performing a predetermined control on the video signal processing unit 7 based on the predetermined data d1 from the comparator 3 and the count data from the counter 5, and 7 is Brightness circuit 7a and contrast circuit 7b that determine the brightness and contrast of the image
And the like are provided in the video signal processing unit.

Next, the operation of the present invention will be described. The analog video signal is converted into a digital video signal by the A / D conversion unit 1, and the APL detection unit 2 converts the digital video signal.
To detect APL. The detected APL data Dn is sent to the comparator 3 and the flip-flop 4. As the APL detection method, there is another method other than the above, in which the APL is detected in the state of the analog video signal and the detected APL is digitally converted to obtain APL data, but any method may be used. The comparator 3 constantly compares the APL data Dn (current APL data) corresponding to the current video signal sent from the APL detector 2 with the APL data one field before in time. Here, the APL data one field before is the data one field before the current average video level data when the APL changes,
When the APL does not change and is constant, the first data becomes constant. This is because the flip-flop output, which will be described later, is latched by the first data that has become constant.

Then, the comparator 3 outputs the current APL data.
Dn is compared with the data one field before, and when the two data are different, that is, when the APL is changing, a predetermined data d1 [for example, a high level (H) signal] is output to change both data. If there is not, that is, if there is no change in APL, the d1 is not output. The “APL data one field before” is fed back from the flip-flop 4. The flip-flop 4 has the current APL as shown.
The data Dn and the predetermined data d1 are input. And
Due to the nature of the flip-flop, when there is d1, this causes Dn to be output, and unless a new d1 is input next, Dn
Latch (hold). That is, when d1 is input, the output of the flip-flop 4 is updated with new APL data, and the updated data becomes the data one field before. If no new d1 is input, the latest updated data is the data one field before.

The type of the flip-flop 4 is not particularly limited as long as it has the above-mentioned function such as a D-type flip-flop. The predetermined data d1 is sent to the counter 5 and the control unit 6. The counter 5 is used for time measurement, and as a method thereof, counts signals in vertical cycles. The vertical cycle is fixed (16.7 mS for the NTSC system), and the time can be determined by counting this. For example, a vertical synchronizing signal is used as the signal of the vertical cycle. Predetermined data d1 output from the comparator 3
Is used as a reset signal for the counter. That is, A
When there is a change in PL, the reset is used as a starting point to start counting. The count data is sent to the control unit 6.

When the predetermined data d1 is input, the control unit 6 monitors it based on the count data from the counter 5. Then, when the state of the same d1 continues for a predetermined count number (= predetermined time), the same video continues. In this case, the video signal processing unit 7 is controlled to reduce the brightness of the video. Specifically, the luminance circuit 7a lowers the luminance, the contrast circuit 7b lowers the contrast, or both are used in combination. The rate of lowering is predetermined, for example, the current brightness is several tens of percent.
Lower. This prevents image sticking on the PDP display surface. When new predetermined data is input while the predetermined data d1 monitored by the control unit 6 does not reach the predetermined count number, the video is not the same video but the video signal processing unit 7 is changed. No control is required.

[0011]

As described above, according to the present invention, mainly in a monitor using a PDP, a change in the average video level (APL) of an input video signal is constantly monitored, and the same AP is used.
When L does not change for a predetermined time, it is determined that the image is in a still image state, and the brightness of the image is reduced at a predetermined rate. Therefore, it is possible to prevent burn-in of the PDP display surface and unnecessary heat generation that occur when the same image continues for a long time. In particular, the present invention is effective when a high-luminance video such as a NES or a teletext broadcast continues for a long time in a still image state.

[Brief description of drawings]

FIG. 1 is a block diagram of an essential part of an embodiment of a display surface burn-in prevention circuit according to the present invention.

[Explanation of symbols]

 1 A / D converter 2 APL detector 3 Comparator 4 Flip-flop 5 Counter 6 Controller 7 Video signal processor 7a Luminance circuit 7b Contrast circuit

Claims (6)

[Claims] 1. A comparator for comparing current average video level data with average video level data one field before the current average video level data, and outputting predetermined data when both data do not match, and the current A latch circuit that outputs the average video level data of the preceding field based on the average video level data and the predetermined data from the comparator, and the predetermined data output from the comparator as a reset signal, When a counter for counting, predetermined data output from the comparator and count data from the counter are input, and the predetermined data has not been input by the time the count data reaches a predetermined limit value, an image is displayed. A control unit that controls the video signal processing unit so as to reduce the brightness of the image to a predetermined brightness. A display surface burn-in prevention circuit characterized by being configured with. 2. The image sticking prevention according to claim 1, wherein the latch circuit updates the output of the latch circuit to the current average video level data every time a predetermined data is input. circuit. 3. The display surface burn-in prevention circuit according to claim 1, wherein the latch circuit is composed of a flip-flop circuit. 4. The display surface burn-in prevention circuit according to claim 1, wherein the reduction in the brightness of the image by the control unit is reduced by controlling the luminance circuit in the video signal processing unit. . 5. The reduction in the brightness of the image by the control unit is reduced by controlling a contrast circuit in the image signal processing unit.
Circuit for preventing image sticking on the display surface. 6. The display surface burner according to claim 1, wherein the decrease in the brightness of the image by the control unit is decreased by controlling both the brightness and the contrast in the image signal processing unit. Prevention circuit.