Circuit for regulating brightness and size of picture in display apparatus

This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application for ALC And Size Regulation Circuit Of Display Apparatus earlier filed in the Korean Industrial Property Office on the 13 th of Feb. 1999, and there duly assigned Ser. No. 5286/1999, a copy of which application is annexed hereto.

The present invention relates to a display apparatus. More specifically, the present invention relates to a circuit for regulating the brightness and size of picture in a display apparatus, in which a picture brightness regulating circuit and a picture size regulating circuit are organically coupled together, and the picture brightness and size are decided by utilizing composite adjusting signals of a microcomputer, in view of the fact that the picture brightness and size are decided by the beam currents flowing from a fly back transformer to a cathode ray tube.

Generally, the brightness regulating circuit of a display apparatus prevents the brightness level of picture from rising too high, so that the picture brightness of the display apparatus would be constant all the time. Therefore, the intensities of the beam currents which are supplied to the cathode ray tube are fed back to the brightness regulating circuit. Thus if the intensity of the feedback beam current is higher than a certain level, then the clamp levels of the RGB video signals which are inputted into the brightness regulating circuit are made to be restricted by a predetermined level, so that the intensities of the beam currents would not rise any more.

Meanwhile, the picture size regulating circuit of the display apparatus regulates the picture size which is varied in accordance with the variation of the high voltage. This picture size regulating circuit is generally applied to a high voltage/horizontal deflection integral type display apparatus in which the high voltage is not constant, and in which the picture size is varied in accordance with the intensity of the beam current.

In other words, if the high voltage is varied, then the picture size is varied, and if the high voltage is varied, then the intensities of the beam currents are also varied. As described above, there is a close relationship between the variation of the high voltage and the variation of the intensities of the beam currents. Therefore, the picture size regulating circuit detects any variation of the intensities of the beam currents, and decides the picture size based on the detected intensities of the beam currents. Therefore, this picture size regulating circuit can easily regulate the picture size in the high voltage/horizontal deflection integral type display apparatus.

What is needed is the maximum brightness restriction line and the picture size regulating degree are decided by the composite adjusting signals of the microcomputer. Therefore, the manufacturing time can be saved during the manufacture of the display apparatus, and therefore, the productivity can be improved. Further, the constitution of the brightness and picture size regulating circuit section is very simple, and therefore, the economy is improved during its designing.

Therefore it is an object of the present invention to provide a circuit for regulating the brightness and picture size in a display apparatus, in which a picture brightness regulating circuit and a picture size regulating circuit are organically coupled together, and the picture brightness and size are decided by utilizing composite adjusting signals of a microcomputer.

In achieving the above object, in a display apparatus for receiving and amplifying RGB signals from a computer main body to output them to a cathode ray tube, for supplying a high voltage from a fly back transformer to the cathode ray tube, and for carrying out horizontal deflections by a horizontal deflecting circuit, the circuit for regulating the brightness and picture size for the display apparatus according to the present invention includes: a current sensing section for sensing intensities of beam currents incoming into the cathode ray tube; a microcomputer for deciding a lower limit of a terminal voltage if the terminal voltage is lowered, the terminal voltage being anti-proportional to the beam current as sensed by the current sensing section; and a brightness and picture size regulating circuit section for deciding an upper limit of the terminal voltage in relation to an internal power and an internal impedance of a video pre-amplifier, for outputting brightness regulating signals to the video pre-amplifier to adjust the clamp level of RGB video signals if the terminal voltage departs from the lower limit of the microcomputer, and for outputting horizontal/vertical size regulating signals to a deflecting circuit section to regulate a picture size.

In the conventional display apparatus, a brightness regulating circuit and a picture size regulating circuit are separately made. And brightness regulating signals and horizontal/vertical size regulating signals inputted to the brightness regulating circuit and a picture size regulating circuit are outputted separately from the microcomputer. However, in the present invention, brightness and picture size regulating circuit section is made as one circuit and composite adjusting signals outputted from a microcomputer are inputted into the brightness and picture size regulating circuit section in order to adjust brightness and picture size of a monitor.

A more complete appreciation of the invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein:

FIG. 1 is a block diagram showing the constitution of the conventional automatic picture brightness and size regulating circuit for a display apparatus;

FIG. 2 is a detailed circuit diagram for the circuit of FIG. 1;

FIG. 3 illustrates the upper and lower limits of the conventional picture brightness and size regulating unit;

FIG. 4 is a block diagram showing the constitution of the automatic picture brightness and size regulating circuit for a display apparatus according to the present invention;

FIG. 5 is a detailed circuit diagram for the circuit of FIG. 4;

FIG. 6 illustrates the upper and lower limits of the picture brightness and size regulating circuit according to the present invention; and

FIG. 7 is a block diagram illustrating roughly FIG. 5 .

FIG. 1 is a block diagram showing the constitution of the conventional picture brightness and size regulating circuit for a display apparatus. FIG. 2 is a detailed circuit diagram for the circuit of FIG. 1 . FIG. 3 illustrates the upper and lower limits of the conventional picture brightness and size regulating circuit.

The constitution of the conventional picture brightness and size regulating circuit will be described referring to FIGS. 1 to 3 . A current sensing section 10 senses the intensities of the beam currents which flow from an FBT (flyback transformer) to a cathode ray tube. A driving section 20 outputs voltages which are anti-proportional to the intensities of the beam currents which are derived from the current sensing section 10 . The driving section 20 includes resistors R 1 andR 2 and a diode D 2 , and the resistors R 1 and R 2 decide the upper limit of the voltages which are outputted anti-proportionally to the intensities of beam currents, while the diode D 2 decides the lower limit of the voltages.

A microcomputer 30 outputs brightness regulating signals to a brightness regulating section 40 , and outputs horizontal/vertical size regulating signals to a picture size regulating section 50 .

The above mentioned brightness regulating signals are for deciding the brightness restricting limit. The brightness restricting limit is that which has been decided by the supervisor at the production line by directly measuring the brightness by means of an automatic measuring instrument.

The horizontal/vertical size regulating signals which are inputted into the picture size regulating section 50 are for regulating the derived signals which are derived by the current sensing section 10 from the intensities of the beam currents by varying the regulating degree. The horizontal vertical size regulating signals make it possible to adjust the regulating degree.

The horizontal/vertical size regulating signals are the regulation amounts which are decided by the supervisor at the production line by directly measuring the brightness by means of an automatic measuring instrument.

The brightness regulating circuit 40 receives the output voltages of the driving section 20 through a transistor Q 1 . If the levels of the brightness and size regulating signals which have been formed by the above described voltages are higher than a predetermined level, then the brightness regulating signals are outputted to a video pre-amplifier (not illustrated).

Then the video pre-amplifier lowers the clamp level of the RGB video signals in response to the brightness regulating signals, so that the brightness of the display apparatus would be regulated, thereby regulating the brightness of picture.

The picture size regulating circuit section 50 receives the output voltages of the driving section 20 through transistors Q 2 and Q 3 . If the received voltage level is higher than a certain level, the horizontal/vertical size regulating signals are outputted to a deflecting circuit (not illustrated), thereby forcibly regulating the horizontal/vertical picture size.

Here, reference codes R 3 -R 14 are resistors, C 1 -C 5 are capacitors, and D 1 and D 3 are diodes.

The conventional automatic brightness and picture size regulating circuit of the display apparatus constituted as above will be described as to its operations. First, the output voltages of the driving section 20 are weakened if the intensities of the beam currents becomes high as sensed by the current sensing section 10 , while they are strengthened if the latter are weakened. That is, the stronger the intensities of the beam currents become, the higher the brightness becomes, with the result that the picture becomes gradually brighter.

Under this condition, the upper limit of the output voltages of the driving section 20 is decided by the divided voltage as divided by the resistors R 1 and R 2 , while the lower limit is decided by the diode D 2 . Thus the lower limit becomes about −0.7 V. Therefore, the output voltages of the driving section 20 have values between the upper limit and the lower limit. This is illustrated in FIG. 3 .

Meanwhile, if the beam current as sensed by the current sensing section 10 is steeply increased, then the output voltages of the driving section are lowered. Consequently, the transistors Q 1 and Q 2 of the brightness regulating section 40 and the picture size regulating section 50 are turned off. Therefore, the brightness regulating section 40 outputs the brightness regulating signals of the microcomputer 30 to a video pre-amplifier (not illustrated) so as to lower the clamp level of the RGB video signals.

Thus the brightness level of the display apparatus can be prevented from becoming too high, and the picture brightness is maintained at a constant level all the time. Under this condition, the brightness adjusting signals which are outputted from the microcomputer 30 are for deciding the picture brightness restriction line. This picture brightness restriction line is a brightness level which has been measured by using an automatic instrument during the manufacture.

Like when regulating the brightness level, if the output voltages of the driving section 20 are steeply lowered, then the picture size regulating section 50 outputs the horizontal/vertical size regulating signals of the microcomputer 30 to the deflecting circuit (not illustrated), thereby forcibly regulating the picture size.

The horizontal/vertical size regulating signals of the microcomputer 30 are the regulation amounts which have been measured by using an automatic instrument during the manufacture of the display apparatus like in the case of the brightness regulating signals.

As shown in FIG. 2, the brightness regulating circuit section 40 and the picture size regulating circuit section 50 include transistors Q 1 , Q 2 and Q 3 . This is for ensuring that the two circuit sections should not influence to each other when the two circuit sections receive the variations of the intensities of the beam currents from the current sensing section 10 .

That is, the brightness regulating circuit section 40 regulates the brightness of the display apparatus through its own processing, while the picture size regulating circuit section 50 regulates the picture size of the display apparatus through its own processing. Thus the two sections are separated, so that there would be no mutual influence between the two circuit sections. Therefore, the circuit sections 40 and 50 can accurately operate by separately receiving the variations of the intensities of the beam currents.

However, in the above described conventional technique, the brightness regulating section 40 and the picture size regulating section 50 have complicated structures. Further, if the beam current is increased, the brightness and the picture size are regulated by receiving the horizontal/vertical size regulating signals from the microcomputer. Therefore, the brightness regulating signals and the horizontal/vertical size regulating signals have to be measured and set up during the manufacture of the display apparatus. Consequently, the time for manufacturing the display apparatus is extended, and the manufacturing operation becomes very troublesome.

FIG. 4 is a block diagram showing the constitution of the automatic picture brightness and size regulating circuit for a display apparatus according to the present invention. FIG. 5 is a detailed circuit diagram for the circuit of FIG. 4 . FIG. 6 illustrates the upper and lower limits of the picture brightness and size regulating circuit according to the present invention. FIG. 7 is a block diagram illustrating roughly FIG. 5 .

The automatic picture brightness and size regulating circuit according to the present invention is constituted as follows. A current sensing section 100 senses the intensities of the beam currents which flow from a flyback transformer (FBT) to a cathode ray tube. The beam currents and the brightness are changed by first and second grids G 1 and G 2 operated by accepting a voltage outputted from the second wire of the FBT. In order to generate the pertinent beam current and brightness, the first wire operating time of the FBT is adjusted by using a PWM signal. Accordingly, the FBT can be called conceptually current sensing section. A microcomputer 300 decides a lower limit, so that a terminal (a of FIG. 5) voltage can be prevented from being lowered to below a certain level, if the terminal voltage is lowered anti-proportionally to the beam current as sensed by the current sensing section 100 . Under this condition, the mentioned lower limit is a value which decides the maximum brightness restriction line and the picture size regulating degree in the display apparatus.

A brightness and picture size regulating circuit section 400 decides the upper limit of the terminal (a of FIG. 5) voltage so that the terminal voltage can be prevented from being too much lowered anti-proportionally to the intensity of the beam current as sensed by the current sensing section 100 . The upper limit of the terminal voltage is decided in relation to the internal power and the internal impedance of a video pre-amplifier 200 . Further, the brightness and picture size regulating circuit section 400 outputs brightness regulating signals ACL or auto contrast limit which is equal to ABL or auto brightness limit, to the video pre-amplifier 200 to adjust the clamp level of RGB video signals if the terminal voltage departs from the lower limit of the microcomputer 300 . Further, the brightness and picture size regulating circuit section 400 outputs horizontal/vertical size regulating signals to a deflecting circuit to regulate the picture size.

The terminal (a of FIG. 5) of the brightness and picture size regulating circuit section 400 is connected to a plurality of resistors R 15 and R 16 . In order to decide the upper limit, the plurality of the resistors R 15 and R 6 divide the voltage of the internal power of the video pre-amplifier 200 .

Meanwhile, besides the plurality of the resistors R 15 and R 16 , the brightness and picture size regulating circuit section 400 includes a plurality of diodes D 4 -D 7 (which block the reverse voltage), so that the brightness regulating signals supplied to another video pre-amplifier (not illustrated) and the horizontal/vertical size regulating signals supplied to the deflecting circuit would not be influenced by composite regulating signals of the microcomputer 300 . Further, the brightness and picture size regulating circuit section 400 includes: a resistor R 17 for adjusting the adjustment sensitivity of the brightness and picture size regulating signals of the microcomputer 300 ; and resistors R 18 and R 19 for regulating the difference between the brightness and picture size regulating signals. Further, the brightness and picture size regulating circuit section 400 is connected to vertical size and horizontal size regulating signal outputting terminals.

Reference code C 6 indicates a capacitor which adjust the speed of responding to the horizontal size regulating signals.

Now the circuit for regulating the brightness and picture size in a display apparatus according to the present invention will be described as to its operations by referring to the attached drawings.

As shown in FIGS. 4 and 5, the brightness regulating signals are inputted into the video pre-amplifier 200 which is the first amplifying device for amplifying the RGB video signals. If the brightness regulating signal which is inputted into the video pre-amplifier 200 has a level of over 4.3 V, then a brightness restriction line is not formed by the brightness and picture size regulating circuit section 400 . However, if the brightness regulating signal which is inputted into the video pre-amplifier 200 has a level of less than 4.3 V, then a brightness restriction line is formed by the brightness and picture size regulating circuit section 400 .

To describe it in more detail, if the intensity of the beam current as sensed by the current sensing section 100 is increased, then the terminal (a of FIG. 5) voltage is lowered. Under this condition, the terminal voltage is lowered only to the lower limit which has been set up by the microcomputer 300 . On the other hand, if the intensity of the beam current is lowered, then the terminal voltage rises owing to the internal power of the video pre-amplifier 200 . Under this condition, the rising degree of the terminal voltage is limited by the upper limit which has been described above.

As shown in FIG. 6, as to the upper and lower limits, the terminal voltage is varied in accordance with the beam currents of the current sensing section 100 . That is, the lower limit is decided by the composite adjusting signals of the microcomputer 300 , while the upper limit is decided by the internal divided voltage and by the internal impedance of the video pre-amplifier 200 .

Therefore, as described above, even if the terminal voltage is lowered due to a continuous increase in the intensity of the beam current (as sensed by the current sensing section 100 ), the terminal voltage does not go down below the lower limit, because the lower limit has been already established.

Generally, the lower limit makes the voltage level of the brightness regulating signal input terminal of the video pre-amplifier slightly lower than 4.3 V. Further, the lower limit adjusts the clamp level of the RGB video signals of the video pre-amplifier 200 so as to serve as a restriction line for restricting the brightness of the display apparatus to below a certain value.

Thus the maximum brightness restriction line is decided by the composite adjusting signals of the microcomputer 300 , while the variation range of the picture size regulating signals is decided so as to decide the picture size regulating degree.

FIG. 7 shows a constitution wherein devices of FIG. 5 are divided as a block according to the function thereof. In FIG. 7, there are illustrated a bias circuit section 410 consisted of resistance R 15 and R 16 , a condenser C 6 which is a response speed controller 420 , a cut-off circuit section 430 for cutting off a reverse bias voltage consisted of diodes (D 4 -D 7 ) and a compensation circuit section 440 consisted of resistance R 17 , R 18 and R 19 . The compensation circuit section is to regulate error when there is any error generated from composite adjusting signals, horizontal size regulating signals and vertical size regulating signals because of regulating based on brightness regulating signals.

According to the present invention as described above, the maximum brightness restriction line and the picture size regulating degree are decided by the composite adjusting signals of the microcomputer. Therefore, the manufacturing time can be saved during the manufacture of the display apparatus, and therefore, the productivity can be improved. Further, the constitution of the brightness and picture size regulating circuit section is very simple, and therefore, the economy is improved during its designing.