KR20020061055A - Automatic brightness control apparatus for a monitor - Google Patents

Abstract

PURPOSE: A device for automatically adjusting the luminance of a monitor is provided to maintain raster luminance of the monitor at a constant level by uniformly maintaining a deviation between a G1 voltage and the cutoff voltage. CONSTITUTION: A high voltage detecting circuit(200) receives a high voltage from an FBT(Fly Back Transformer) to output a constant voltage. A reference voltage controlling circuit(210) adjusts and outputs a cutoff voltage according to the voltage output from the high voltage detecting circuit. A cutoff voltage controlling circuit(220) receives the cutoff voltage from the reference voltage controlling circuit, and outputs the inputted cutoff voltage to an R/G/B(Red/Green/Blue) cathode. The high voltage detecting circuit including resistances(R1,R2) and a zener diode(ZD1) divides voltage(Va) output from the FBT by the resistances, and outputs the constant voltage by adding a voltage fed to the resistance(R2) and a voltage fed to the zener diode.

Description

Automatic brightness control device for monitors {AUTOMATIC BRIGHTNESS CONTROL APPARATUS FOR A MONITOR}

The present invention relates to a brightness adjustment device that automatically adjusts the brightness of a monitor, and more particularly, in a high pressure / deflection integrated monitor in which a high pressure varies depending on a horizontal frequency, for compensating for a raster brightness varying according to a mode. It relates to a brightness adjustment device.

1 is a block diagram schematically showing a driving circuit of a conventional monitor. The operation of the conventional monitor will be briefly described with reference to FIG.

First, the CRT consists of a high vacuum glass tube, an electron gun, and a fluorescent surface, and the electron beam emitted from the electron gun strikes the fluorescent surface to reproduce an image. At this time, the electron gun is a device that elongates the hot electrons into a thin electron beam and collides with the fluorescent surface. The electron gun emits a cathode, a control grid G1 for controlling the amount of the beam, a grid G2 for accelerating the electron beam, and a beam focus control. Grids G3 and G4 serving as lenses.

Then, a high voltage is generated from a flyback transformer (hereinafter referred to as "FBT") and supplied to the CRT, and a negative voltage generated in the FBT is controlled by a G1 voltage controller to control the grid G1 terminal described above. Supplied to.

Meanwhile, an R / G / B output representing an R / G / B signal, which is an image signal, is coupled to the R / G / B cutoff voltage generated by the cutoff voltage controller and C1, C2, and C3 to the R / G / B cathode. Is entered.

In such a monitor, the luminance is determined by the deviation of the G1 voltage and the cut-off voltage of the R / G / B cathode.

However, in the case of the high pressure / deflection integrated monitor, the magnitude of the beam current is different for each mode, and accordingly, the magnitude of the high pressure applied to the CRT varies according to each mode. As a result, the high voltage rises in the low horizontal frequency mode, and as the high voltage increases, the negative voltage applied to the G1 terminal also increases. That is, the negative voltage increases in the low horizontal frequency mode.

Therefore, in the conventional monitor, the cutoff voltage is always kept constant by the cutoff voltage controller, while the G1 voltage is changed depending on the horizontal frequency according to the mode of the monitor. As a result, when the mode of the monitor is changed, the deviation of the cutoff voltage and the G1 voltage is changed, and the brightness of the monitor is also changed. That is, the conventional monitor has a problem that the raster brightness is changed for each mode by the change of the G1 voltage.

SUMMARY OF THE INVENTION An object of the present invention is to provide a monitor having a constant raster brightness at all times even if the mode is changed by preventing the raster brightness of the monitor from changing according to each mode.

1 is a block diagram schematically showing a driving circuit of a conventional monitor.

2 is a circuit diagram showing a brightness adjusting device of a monitor according to the present invention;

3 is a graph showing the change of high pressure according to the horizontal frequency.

4 is a graph showing the change of Va with high pressure.

5 is a graph showing changes in the cutoff voltage and the G1 voltage according to high pressure.

The brightness adjustment device of the monitor of the present invention for achieving the above object,

A high voltage detector detecting a magnitude of the high voltage output from the FBT, a reference voltage controller adjusting and outputting a cutoff voltage according to a constant voltage output from the high voltage detector, and a cutoff voltage received from the reference voltage controller. A cutoff voltage control unit outputs the / B cathode.

In this case, the high pressure sensing unit includes resistors R1 and R2 and a zener diode, and the voltage Va output from the FBT is divided by the resistors R1 and R2, and the voltage applied to the resistor R2 and the zener are divided. The voltages applied to the diodes are summed and input to the reference voltage controller.

More preferably, the reference voltage controller includes a first transistor, a second transistor, and resistors R3, R4, and R5, and a voltage output from the high voltage sensing unit is applied to the base of the first transistor. The collector of the first transistor is connected to the base of the second transistor and one end of the resistor R4, and the emitter of the first transistor is connected to ground via the resistor R3. In addition, the base of the second transistor is commonly connected to the resistors R4 and R5 and the collector of the first transistor, and is connected to the ground through the resistor R5, and the collector of the second transistor is powered and The emitter of the second transistor is connected to the cutoff voltage controller, one end of the resistor R5 is connected to the collector of the second transistor, and the other end is connected to the base. In addition, one end of the resistor R4 is connected to the base of the second transistor and the other end is grounded.

According to the present invention, by detecting the high pressure of the FBT and adjusting the raster luminance, it is possible to compensate for the luminance difference due to the difference in luminance according to the horizontal frequency or the difference in the high pressure in the same mode.

Hereinafter, with reference to the accompanying drawings will be described in detail the configuration and operation of the brightness adjustment apparatus of the monitor according to the present invention.

2 is a circuit diagram showing a brightness adjustment apparatus of the monitor according to the present invention.

First, with reference to FIG. 2, the structure of a brightness adjustment apparatus is demonstrated.

According to an exemplary embodiment of the present invention, a luminance compensation circuit includes a high voltage detector 200 for detecting a magnitude of a high voltage output from an FBT, a reference voltage controller 210 for adjusting a magnitude of a cutoff voltage, and a cutoff voltage of an R / G / B cathode. And a cutoff voltage control unit 220 for outputting the control circuit.

The high pressure detector 200 is a circuit for receiving a high voltage Va output from the FBT and outputting a constant voltage to the reference voltage controller. The high voltage detector 200 includes resistors R1 and R2 and a zener diode ZD1. The high voltage detecting unit divides Va output from the FBT by the resistors R1 and R2, and outputs a constant voltage obtained by adding the voltage applied to the resistor R2 and the voltage applied to the zener diode.

The reference voltage controller 210 is a circuit for controlling the voltage input to the cutoff voltage controller according to the magnitude of the constant voltage output from the high voltage detector, and includes a first transistor Q1, a second transistor Q2, and a resistor R3,. R4, R5).

In the first transistor Q1, the base is connected to one end of the zener diode of the high voltage sensing unit, the emitter is grounded through the resistor R3, and the collector is connected to the base and the resistor R5 of the second transistor. It is connected to the collector of the second transistor via the resistor R4 and grounded via the resistor R5.

In the second transistor Q2, the base is connected to the collector and resistor R5 of the first transistor, and the collector is input with a voltage Vc output from a switching mode power supply (SMPS) circuit, which is a power supply circuit. The emitter is connected to the input of the cutoff voltage controller 220. Meanwhile, one end of the resistor R4 is connected to the collector of the second transistor, the other end is connected to the base of the second transistor, one end of the resistor R5 is connected to the base of the second transistor, and the other end is grounded.

The cutoff voltage controller 220 is a circuit that receives a cutoff voltage from the reference voltage controller 210 and provides cutoff voltages to R / G / B cathodes, respectively.

The operation of the monitor brightness adjusting device of the present invention having the above-described configuration will be described below.

In the high voltage / deflection integrated monitor, the horizontal frequency varies according to the mode, and the magnitude of the beam current controlled by the ABL controller varies according to the horizontal frequency. As a result, as shown in FIG. 3, which is a graph showing the change of the high pressure according to the horizontal frequency, the magnitude of the high pressure applied to the CRT varies according to the horizontal frequency.

In addition, as shown in FIG. 4, which is a graph showing the change of the negative voltage and the Va voltage according to the high pressure, the high voltage also affects the negative voltage applied to the control grid G1 which controls the amount of the electron beam. do. The negative voltage is adjusted to the appropriate G1 voltage by the G1 voltage control unit and applied to the G1 terminal of the CDT. That is, the G1 voltage is changed for each mode according to the horizontal frequency.

On the other hand, the raster brightness of the monitor is determined by the deviation between the G1 voltage and the cutoff voltage. However, in the conventional monitor, the G1 voltage varies depending on the mode, but the cutoff voltage is always constant by the cutoff voltage controller, so that the deviation ΔV between the G1 voltage and the cutoff voltage varies depending on the mode. That is, in the monitor, since the luminance is determined by the deviation between the G1 voltage and the cutoff voltage, the deviation varies according to each mode, and the raster luminance of the monitor also changes.

In order to solve the conventional problems, the present invention compensates the raster luminance of the monitor by adjusting the cutoff voltage according to the change of the high voltage so that the deviation between the G1 voltage and the cutoff voltage is always maintained regardless of the mode.

First, the high voltage detecting unit 200 detects the voltage Va output from the FBT, the detected voltage is divided by the resistors R1 and R2, and the voltage applied to the resistor R2 and the zener diode ZD1. The voltages applied to the sum are applied to the base of the first transistor of the reference voltage controller 210.

In this case, the constant voltage Vref applied from the high voltage sensing unit to the base of the first transistor of the reference voltage controller is as follows.

Vref = V _ZD1 + [R2 / (R1 + R2)] * Va

The voltage Vref applied to the reference voltage controller 210 is determined by the voltage Va as shown in the equation. Therefore, when the high voltage output from the FBT rises, Va also rises, and the voltage Vref input to the reference voltage controller increases.

When the voltage Vref is applied to the base of the first transistor Q1 of the reference voltage controller, the voltages Ve, Ie, and Ic applied to the emitter of the first transistor are as follows.

Ve = Vref-Vbe

Ie = (Ve of Q1) / R3

Ic = Ie

Therefore, Vref applied to the base of the first transistor controls the collector current Ic of the first transistor. That is, controlling the Ic current is the Ve voltage of the first transistor, and the Ve voltage of the first transistor is controlled only by Va. Therefore, when the Va voltage increases, the Ve voltage and the Ic current of the first transistor increase together, and the current I1 flowing through the resistor R4 also increases.

In summary, when the high pressure output from the FBT rises, Va and I1 increase together. However, when I1 increases, the voltage applied across the resistor R4 increases and the base voltage of the second transistor decreases. That is, the base voltage Vb and the emitter voltage Ve of the second transistor are as follows.

Vb = Vc-[(I1 + Ic) * R4]

Ve = Vb-Vbe

Therefore, when I1 increases, the Vb voltage of the second transistor is lowered and the Ve voltage is also lowered.

The emitter voltage Ve of the second transistor of the reference voltage controller is applied to the cutoff voltage controller as a cutoff voltage. When the high voltage rises, a low Ve is applied to the cutoff voltage controller. Otherwise, a high Ve is applied.

The cutoff voltage is applied to the R / G / B cathode by the cutoff voltage controller, respectively, and the raster brightness of the monitor is determined by the deviation between the G1 voltage and the cutoff voltage adjusted by the G1 voltage controller.

5 is a graph illustrating changes in the cutoff voltage and the G1 voltage according to the change in the high voltage.

Referring to FIG. 5, in the luminance compensation circuit of the present invention, when the high voltage rises, as the G1 voltage increases and the cutoff voltage decreases, the deviation between the G1 voltage and the cutoff voltage is always kept constant. As a result, the raster luminance of the monitor determined by the deviation between the G1 voltage and the cutoff voltage is always kept constant regardless of the mode.

According to the monitor brightness compensating circuit of the present invention, even if the monitor mode is changed, the raster brightness of the monitor can be kept constant by always keeping the deviation between the G1 voltage and the cutoff voltage by varying the cutoff voltage.

Claims (3)

In the monitor, A high pressure detector for receiving a high voltage from the FBT and outputting a constant voltage; A reference voltage controller which adjusts and outputs a cutoff voltage according to the voltage output from the high voltage sensing unit; Cutoff voltage control unit for receiving a cutoff voltage from the reference voltage control unit, and outputs the input cutoff voltage to the R / G / B cathode A brightness adjustment apparatus comprising a. The method of claim 1, The high pressure sensing unit includes resistors R1 and R2 and a zener diode, and the voltage Va output from the FBT is divided by the resistors R1 and R2, and is applied to the zener diode and the voltage applied to the resistor R2. And the applied voltages are added to the reference voltage controller. The method of claim 1, The reference voltage controller includes a first transistor, a second transistor, and resistors R3, R4, and R5, and the base of the first transistor is supplied with a voltage output from the high voltage sensing unit, and the collector of the first transistor. Is connected to the base of the second transistor, the emitter of the first transistor is connected to ground via a resistor R3, and the base of the second transistor is commonly in common with the resistor R5 and the collector of the first transistor. Connected, The cutoff voltage output to the emitter of the second transistor is adjusted according to the voltage applied to the base of the first transistor.