JPH0520069Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] This invention is a display device in which a plurality of independent displays are lined up to display one image, and each screen is controlled by an ABL (automatic brightness limit) circuit. This relates to a video display circuit that adjusts the brightness of images.

[Prior Art] Conventionally, in this type of device, each display unit has a second
I got what is shown in the figure. In FIG. 2A, 2 is a second video amplification circuit that amplifies the input video signal, 3 is a third video amplification circuit that further amplifies the video signal, and 4 is a cathode ray tube that separates the video signal into luminance and color difference signals. A video output circuit for driving the cathode or grid for display; 5 is a cathode ray tube as a display; 6 is a flyback transformer (FBT)
11 is a high voltage rectifier circuit that generates a high voltage and supplies it to the anode 12 of the cathode ray tube 5; 7 is a horizontal output circuit that drives the horizontal deflection yoke of the cathode ray tube;
8 detects the anode current of the cathode ray tube from a part of the horizontal output circuit 7 through the ABL adjustment volume 10 and appropriately drives the brightness adjustment volume 9.
It is an ABL circuit.

Generally, in an ABL circuit, when the brightness of the cathode ray tube 5 becomes abnormally high, excessive current flows through the cathode ray tube 5, overloading the high voltage rectifier circuit 6, and destroying the transistors used in the horizontal output circuit 7. This is a circuit that prevents this from happening.

As a means for this purpose, the ABL circuit 8 detects changes in the input current of the flyback transformer (FBT) 11 and controls the voltage supplied to the brightness adjustment volume 9. And a third video amplification circuit 3 and a video output circuit 4
By providing negative feedback through the beam, the beam current of the cathode ray tube 5 is limited to a specified value or less. The ABL adjustment volume 10 is a volume for setting within this specified value.

Figure 2B is an example of this circuit, in which changes in the horizontal output current caused by fluctuations in the load of the high-voltage circuit are detected across the emitter resistor R2 of the horizontal output transistor Q1, and smoothed by the resistor R3, diode D1, and capacitor C1. and added to the base of ABL transistor Q2. On the other hand, a positive bias voltage is applied to the emitter from the power supply +B through the ABL adjustment volume 10 to adjust the beam current so that it does not exceed a specified value.

Therefore, when the emitter current of the horizontal output transistor Q1 increases in proportion to the beam current of the cathode ray tube 5, the base voltage of the ABL transistor Q2 increases and the collector voltage decreases. Therefore, the voltage taken out from the movable terminal of the brightness adjuster 9,
That is, the base voltage of the third video amplification transistor Q3 also decreases. Therefore, the base voltage of the video output transistor Q4 decreases and the collector voltage increases. As a result, the cathode voltage of the cathode ray tube increases, so the beam current within the cathode ray tube decreases and the horizontal output current is limited.

Further, the contrast, which is the gradation of brightness and darkness of an image, is generally adjusted by changing the amplification degree of the video output circuit and changing the amplitude of the video signal applied to the cathode ray tube. For example, in FIG. 2B, if you turn the contrast adjustment volume 13 connected to the emitter side of the video output transistor Q4,
The amount of negative feedback of the video output circuit changes, and the degree of amplification changes. As a result, the amplitude of the video signal appearing at the collector of transistor Q4 changes, resulting in a change in the contrast of the image.

Furthermore, according to the "multi-tube television receiver" disclosed in Japanese Patent Application Laid-Open No. 60-134560, by detecting the cathode current of each cathode ray tube, each beam current is detected, and the average value of each detected current is calculated. The ABL is applied based on both the peak value and the peak value. Therefore,
Check the detected beam current of each cathode ray tube and calculate the average value.
Since ABL is applied, each cathode ray tube can maximize its luminous ability while ensuring its safety. It also discloses that since the beam current detected by detecting the cathode current of each cathode ray tube is multiplied by the peak value ABL, an accurate peak value ABL can be multiplied without variations due to the characteristics of the cathode ray tube. There is.

[Problems to be solved by the invention] Conventional video display circuits are configured as described above, so it is difficult to arrange multiple displays equipped with these video display circuits and display one image as a whole. If you do so, the brightness will vary for each display.

Furthermore, even if it is a display of a three-tube projector based on the "multi-tube television receiver" of the above-mentioned Japanese Patent Application Laid-Open No. 60-134570 or a multi-tube television, problems within one display may cause problems. If multiple displays are arranged vertically and horizontally, and each display displays a separate image, you may not notice much variation in brightness, but When trying to display one image, if the brightness of each image is different, a unified image will not be created and the overall image quality will deteriorate.

[Means for solving the problem] This invention was made to eliminate the above-mentioned drawbacks, and the contrast and brightness of each display can be adjusted at least by the lowest voltage of the output of the ABL detection circuit of each display. It is an object of the present invention to provide a video display circuit that can uniformly equalize the brightness of each display by adjusting one of the display devices.

[Example] Hereinafter, an example of this invention will be described based on the drawings. In Figure 1, D1, D2,...Dn are
From the ABL output terminals A1, A2...An, for example, take out the ABL output from point K in Figure 2 B and send it to the contrast terminals C1, C2...n, for example, at the P1 point in Figure 2 B (points K and P1 are not connected. ) or/and P2 point, T1, T2,...Tn are resistors whose collectors are connected to a common ground, their emitters are connected in common, and one end is connected to the power supply Vcc. Rn, and the base is connected to the ABL output terminals A1, A2...An of each display via a resistor.
It is a PNP type transistor.

In this circuit, the lowest voltage of each ABL output pulls down the base of that transistor, causing current to flow through that transistor and generating a voltage across resistor Rn, which is applied to the contrast input terminal of each display.

Then, as in the case where the voltage at point K in FIG. 2B drops, for example, point P1 falls, the base of transistor Q3 falls, and the collector of transistor Q4 rises, reducing the beam current of the cathode ray tube and reducing its brightness. This operation is similar in the case of contrast control.

In other words, the display unit with the lowest ABL output level
If the output level is adjusted to the ABL output level, the brightness of the originally high-brightness display will be lowered, and even the abnormally high-brightness display will be adjusted to the lowest brightness, resulting in a constant brightness overall. On the other hand, if you try to match the ABL output level of a display with high brightness, it is necessary to increase the gain of the video amplifier in the internal circuit of that display, since the ABL output level of the display with low brightness is originally low. Otherwise, measures such as increasing the efficiency of the cathode ray tube are required, which is not realistic.

[Effects of the invention] As described above, according to this invention, when displaying an integrated image by arranging each display unit, the ABL
Since we decided to match the brightness or contrast of the display with the lowest output to the other displays, the brightness and/or contrast of any display can be matched, resulting in an overall uniform image with no variations. It will be done.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a video display circuit according to an embodiment of this invention, and FIG. 2 is a block diagram showing a conventional video display circuit. D1, D2,...Dn...Display device, T1, T2,
...Tn...transistor, 5...cathode ray tube,
8...ABL circuit.

Claims (1)

[Scope of utility model registration request] Adjusting at least one of contrast or brightness by anode current flowing through the cathode ray tube,
A video display circuit of a display device capable of displaying an integrated image by arranging a plurality of display devices equipped with a control function, the ABL voltage being the lowest of the ABL voltages of each of the display devices among the plurality of display devices. An image display circuit comprising a detection means for detecting, and simultaneously controlling at least one of the contrast and brightness of the plurality of display devices based on the ABL voltage of the display device having the lowest ABL voltage.