JPS59126384A - Automatic luminance limiting device - Google Patents

Abstract

PURPOSE:To limit automatically the luminance at receiving of an RGB signal by providing an RGB contrast variable circuit and a DC level variable circuit changing a DC level at an RGB contrast variable terminal in response to the increase in an anode current of a picture tube so as to reduce the contrast of the RGB video. CONSTITUTION:In receiving a video having stricking RGB contrast, a voltage at a connecting point TPD1 changes from a positive to a negative value when a beam current of a prescribed value or over flows and a diode 13 is conductive. When an RGB automatic luminance limit control signal is applied to a base of a transistor(TR) 14 (other than the super pause mode), TR9, 14 are turned on, a voltage at an RGB contrast variable terminal T1 is decreased, an RGB output level is decreased and the luminance of video is reduced. In receiving the super pause, a base of TR14 goes to low potential, the TR9, 14 are turned off and the RGB automatic luminance limit is not operated.

Description

[Detailed description of the invention] Industrial applications This invention enables character multiplex signals to be used in television receivers.

Automatic brightness limiting device (1) that automatically limits the brightness of an RGB image when receiving an RGB signal of a captain signal.

Conventional configuration and its problems Currently, in many television receivers, the current flowing through the flyback transformer, that is, the change in the picture tube anode current, is detected and negative feedback is sent to the video amplification circuit to adjust the beam current of the picture tube. Bright, easy-to-see images are obtained using an automatic brightness limiting circuit that limits brightness to below a specified value. By the way, currently personal computers are using RGB based on character multiplex signals.
A television receiver equipped with a signal input terminal has been developed, but since this input terminal is provided just before each electrode of the cathode ray tube, automatic brightness limitation of the TV double signal is applied to the RGB signals mentioned above. The circuit was not working and the images were difficult to see.

Purpose of the Invention The present invention provides RGB data for character multiplex signals and captain signals.
The purpose of the present invention is to make it easier to view images when inputting signals from an RGB input terminal of a television receiver and receiving RGB signals of a character multiplex signal and a captain signal.

(2) Structure of the Invention The automatic brightness limiting device of the present invention controls the RGB contrast by changing the DC level of the RGB contrast variable terminal.
an RGB contrast variable circuit that changes the contrast of an image; and a DC level variable circuit that reduces the contrast of the RGB image by changing the DC level of the RGB contrast variable terminal in response to an increase in the anode current of the picture tube. By having a configuration that provides
The present invention is characterized in that brightness is automatically limited when a B signal is received to make the screen easier to see.

DESCRIPTION OF THE EMBODIMENTS The drawing shows a circuit diagram of an automatic brightness limiting device according to an embodiment of the present invention. In the drawing, 1 is a flyback transformer, and 2 is an automatic brightness limiting circuit for TV signals. Changes in the current flowing through the flyback transformer 1 are inputted via a capacitor 3 and a resistor 4.5, and the circuit automatically limits the brightness of the TV signal. conduct. 6 is a variable resistor that changes the RGB contrast, and by changing this, the DC level of the RGB (3) contrast variable terminal T changes via the diode 7, and the RG
RG of switching circuit 8 that switches and outputs B signal and TV signal
The output level of the B signal changes in proportion to this. Transistor 9 is for RGB contrast feedback, and a voltage divided by resistor 10 and variable resistor 6 is applied to its emitter. The transistor 90 is connected to the input terminal of the automatic brightness limiting circuit 2 for TV signals via a resistor 11, 12 and a diode 13.

The collector of the transistor 9 is connected to the collector of the RGB automatic brightness limit control transistor 14. The emitter of the transistor 14 is grounded, and the RGB automatic brightness limit control signal is inputted to the base of the transistor 14 from a terminal T through a resistor 15. This RGB automatic brightness limit control signal is a signal that is at the OW level when being received in the Super Bose mode in teletext broadcasting and Captain, and is at the HTGH level at other times.

Next, the operation of this circuit will be explained. Now, when an image with a large RGB contrast is being received, (4) the beam current increases and the voltage at the connection point TPD□ decreases, and when a beam current of more than a certain level flows, it changes from positive to negative. , the diode 13 becomes conductive (normally, the connection point TPD□ is at a positive voltage and the diode 13 is cut off). If at this time, R is applied to the base of transistor 140,
GB automatic brightness limit control signal is added (
(when not in Super Bose mode) and transistor 9.
14 is on, υ, the emitter potential of transistor 9 decreases, and the voltage at the RGB contrast variable terminal T□ decreases.
As a result, the RGB output level is reduced, and the brightness variation of the image is reduced.

Next, when a Super Bose image is being received, the base of the transistor 14 is at a LOW level, the transistors 9 and 14 are turned off, and the RGB automatic brightness limiting operation is not performed.

As described above, in this embodiment, when receiving an RGB signal other than the Super Bose mode, the (5) RGB:l control of the switching circuit 7 is performed in response to an increase in the anode current flowing through the cathode ray tube due to the switching operation of the transistors 9 and 14. Since the DC level of the variable terminal T is lowered to reduce the contrast of the RGB image and brightness is restricted, it is possible to receive a bright and easy-to-see image. Since brightness is not limited, the text can be bright and easy to see even in such cases.

Effects of the Invention According to the automatic brightness limiting device of the present invention, brightness can be automatically limited when receiving RGB images, making it easier to view images.

[Brief explanation of the drawing]

The drawing is a circuit diagram of an embodiment of the present invention. 1... Flyback transformer, 6... Variable resistor, 7
...Diode, 8...Switching circuit, 9...Transistor, 10-12...Resistor, 13...Diode, 14...Transistor, 15...Resistance Agent Patent Attorney Miyai Akio (6)

Claims (1)

[Scope of Claims] (11) An RGB contrast variable circuit that changes the contrast list of an RGB image by changing the DC level of an RGB contrast variable terminal; An automatic brightness limiting device comprising: a DC level variable circuit that reduces the contrast of the RGB image by responsively changing the brightness. An automatic brightness limiting device according to claim (1), which is provided with a switching circuit for switching.