KR20000020425A - Circuit for preventing image enlargement according to luminous intensity - Google Patents

Abstract

PURPOSE: A circuit is provided to prevent an image enlargement focused on a screen and to restrain a diffusion phenomenon on edges of the image by suppressing an emission of electrons in case of increasing a screen brightness. CONSTITUTION: A third transistor(Q3) is operated as a resistor while operated according to a second transistor(Q2). When the third transistor(Q3) is turned on, a fourth transistor(Q4) is turned on. A resistor(R1) is connected to a collector of the fourth transistor(Q4). A capacitor(C3) charges a voltage applied through the resistor(R1) when the fourth transistor(Q4) turns off. A resistance-variable transistor(PM) varies conductivity of a voltage from a source electrode to a drain electrode according to a level of the voltage charged in the capacitor(C3). An error amplifier(EA) varies a voltage state applied to a primary winding of fly back transformer(FBT) according to the voltage from the transistor(PM).

Description

Thwarting circuit of growing image by Lux

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a circuit for preventing the outside of the image from increasing in size due to adjustment of the screen brightness of a television receiver (hereinafter referred to as a TV). Particularly, the variation of the primary voltage of a flyback transformer. The present invention relates to an image enlargement prevention circuit according to illuminance so as to prevent an image from being enlarged on the screen even if the brightness of the screen changes by adaptively adjusting the amount of current.

In general, a TV for receiving and watching a broadcast signal transmitted from a broadcasting station is briefly described with reference to FIG. 1. When a power cord is inserted into an outlet (not shown), a standby power (for example, 5V) is applied to the microcomputer 200. By operating the power "key" of the key input unit 220, a high voltage pulse is generated in the power unit 700 for applying the main power source AC110 / 220V to the FBT 800, and the main power source applied from the power source unit 700. FBT 800 for supplying B ⁺ power to the image processor 300 and the microcomputer 200 for controlling overall operation of the TV by the operation of the key input unit 220, and the microcomputer 200 to process the microcomputer 200. Memory 240 for storing the data to be received, the tuner 100 for receiving the broadcast signal of the channel selected by the tuner voltage output from the microcomputer 200 from the antenna ANT, and the tuner 100 received An image processor 300 for processing an image signal of a broadcast signal The image amplification unit 320 amplifies the image signal output from the image processor 300 and the image signal displayed on the screen of the CRT 400 by the vertical / horizontal synchronization signal processed by the image processor 300. A vertical / horizontal synchronization processor 340 for deflecting a vertical synchronization signal and a horizontal synchronization signal, a CRT 400 for receiving an image signal output from the image amplifier 320 and displaying it on a screen; and the tuner 100. A voice processor 500 for processing a voice signal of the broadcast signal received by the voice signal, a voice amplifier 520 for amplifying the voice signal processed by the voice processor 500 to a predetermined level, and the voice amplifier 520. The speaker 600 is largely configured to receive and output the audio signal output from (620).

2 is a schematic diagram showing an internal structure of a general CRT 400. The heater 410 and the heater 410 that increase the temperature of the cathode 420 by generating heat by receiving an image amplified R, G, and B signals. The cathode 420 emits electrons when a negative voltage is supplied, the control grid 430 modulates the brightness (change in brightness) by adjusting the amount of electrons emitted from the cathode 420, and the cathode ( Acceleration grid 440 that supplies a constant voltage (eg, + 110V to 400V) to attract electrons having a charge and accelerates them in the axial direction so that the electrons emitted from 420 reach the fluorescent tube 492 of the glass tube 490. ), A medium acceleration grid 450 for secondaryly accelerating electrons primarily accelerated by the acceleration grid 440 by supplying a constant voltage (for example, +10 mA or more), and a glass tube discharged from the cathode 420. Electrons traveling toward the fluorescent surface 492 of 490 diffuse by the repulsive force between the electrons. Focusing axially to create a thinner electron beam, and a constant voltage (e.g., electrons emitted from cathode 420 and accelerated twice through acceleration grid 440, medium acceleration grid 450). : The high acceleration grid 470 which supplies +10 kV or more, accelerates in the third order, and collides with the fluorescent surface 492 of the glass tube 490, and the high voltage of a constant voltage (for example, +10 kV) or more. An anode terminal 480 is provided for supplying to the aluminum film of the fluorescent surface 492 and discharging a high voltage when the power is "off".

At this time, if the brightness of the screen is strongly adjusted, the image actually displayed on the screen is distorted as shown in FIG. 3A.

Looking at the causes of the above-mentioned distortion phenomenon, in order to display the image on the CRT screen, it is usually made as a scan of the electron beam generated by the electron gun provided in the CRT driving unit, which is shown in the accompanying Figure 3b As it is. At this time, the horizontal scanning speed at which the electron beam is scanned from left to right on the screen is controlled by the horizontal synchronizing signal, so that the scanning speed is constant.

The scan line period is a period of time required for drawing a raster of a television, a period of horizontal scanning, and a subsequent flyback. The standard value of CCIR is 64 ms, but there is a slight difference due to the difference in broadcasting method. That is, 64 countries use PAL or SECAM and 63.5 countries use NTSC.

In this case, the high brightness of the screen means that the collision energy caused by the electrons colliding on the coronal surface is high, and the high collision energy is caused by the rapid firing speed of the electrons or the large number of electron grains. The phenomenon as shown is generated. That is, as the electron beam that should reach the 'A' point reaches the 'B' point, a distortion phenomenon as shown in FIG. 3A is generated as a whole.

Therefore, in the foregoing description of FIGS. 3A to 3C, the OSD has been described as an example. However, in the actual display image, a spread phenomenon occurs at the outside of the image, and the user is often mistaken for a failure of the TV. As a result, the problem of lowering the reliability of the product and causing unnecessary AS was generated.

An object of the present invention for solving the above problems is to adjust the amount of current in response to the variation of the primary side voltage of the flyback transformer to prevent the image on the screen is enlarged even if the brightness of the screen changes In order to provide an image enlargement prevention circuit according to the illuminance.

1 is a block diagram schematically showing a typical TV receiver

Figure 2 is a schematic diagram showing the internal structure of a typical cathode ray tube (Cathode-Ray Tube: CRT)

3A illustrates an example of distortion occurring under specific conditions when displaying OSD characters.

3B is an exemplary diagram for explaining a scanning speed of an electron beam.

FIG. 3C is an exemplary diagram for describing a cause of distortion illustrated in FIG. 3A.

4 is an exemplary configuration diagram of an image enlargement prevention circuit due to an increase in illuminance according to the present invention.

A feature of the present invention for achieving the above object is that in a Dell receiver having a second transistor for determining whether the primary-side power supply of the flyback transformer is conductive, A third transistor serving as a resistance component, a fourth transistor operating on the basis of the state of the voltage applied to the third transistor as the third transistor is on, and a predetermined positive voltage to the input terminal and the collector terminal of the fourth transistor. A third capacitor which is formed between the resistor to be connected, the connection point of the resistor and the collector terminal of the fourth transistor, and the ground terminal and accumulates a voltage applied through the resistor during the off operation of the fourth transistor, and is accumulated in the third capacitor. The degree of conduction of the voltage across the source terminal to the drain terminal depends on the level of the voltage present. And a resistance variable transistor, having constructed the state of the voltage across the primary winding of the flyback transformer according to the amount of power flowing through the drain of the transistor variable resistance danjaeul to an error amplifier to vary.

Hereinafter, the configuration according to an embodiment of the present invention will be described in detail with the accompanying drawings.

3 is a diagram illustrating a configuration of an image enlargement prevention circuit due to an increase in illuminance according to an embodiment of the present invention. The bridge diode BD receives a commercial AC power and rectifies and converts it into a DC, and the bridge diode BD. The voltage applied to the primary side by the on / off operation of the smoothing first capacitor C1 for smoothing the rectified signal outputted from the first transistor Q1 operated by the control signal of the controller M The conduction is determined and accordingly, the transformer T for transforming and outputting the DC smoothed through the first capacitor C1 to a specific voltage and the voltage output to the secondary side of the transformer T are prevented from being fed back. The conduction of the voltage applied to the primary side by the on / off operation of the first diode (D1) and the second transistor (Q2) operating according to the state of the horizontal synchronization signal is determined and accordingly the first diode A flyback transformer (FBT) that receives the voltage output from the D1 on the primary side and generates power required to return to the next dice in accordance with the horizontal synchronization of the television scan to the secondary side; and the flyback transformer (FBT). The second capacitor C2, which accumulates the voltage applied to the collector terminal of the second transistor Q2, which determines whether the primary-side power supply is turned on, and the second capacitor Q2 A third transistor Q3 which acts as a resistance component, a fourth transistor Q4 which is turned on in accordance with the state of the voltage applied to the third transistor Q3 as the third transistor Q3 is turned on, A predetermined positive voltage is formed between the resistor R1 connecting the input terminal and the collector terminal of the fourth transistor Q4, the connection point of the resistor R1 and the collector terminal of the fourth transistor Q4, and the ground terminal. And award The source terminal according to the level of the third capacitor C3 accumulating the voltage applied through the resistor R1 and the voltage stored in the third capacitor C3 during the off operation of the fourth transistor Q4. The variable resistance transistor (PM) having a different degree of conducting the voltage applied to the drain terminal and the degree of power supplied through the drain terminal of the variable resistance transistor (PM) to the primary side of the flyback transformer (FBT) It consists of an error amplifier (EA) for varying the state of the applied voltage.

An operation of the image enlargement prevention circuit due to the increase in illuminance according to the present invention configured as described above will be described.

The description of the normal operation will be omitted, and the operation of the circuit according to the present invention will be focused on when the brightness of the screen is adjusted.

Once the power is input, the bridge diode BD rectifies the input commercial AC power AC and outputs the DC signal. The rectified DC signal output from the bridge diode BD is the first capacitor C1. ) Is smoothed to maintain a constant voltage.

At this time, the controller M detects that power is being input through the operation state of the photo isolator PI, and accordingly, provides the high signal to the base terminal of the first transistor Q1 at a predetermined cycle.

Therefore, the first transistor Q1 is turned on / off and the transformer T having the primary winding connected to the collector terminal of the first transistor Q1 is turned on / off in the first transistor Q1. As a result, the variation of the DC smoothed through the first capacitor C1 applied to the primary winding is converted into a predetermined voltage and output to the secondary.

The output of the transformer (T) is applied to the primary side of the fly back transformer (FBT) via the first diode (D1) to prevent reverse feedback, the primary winding of the fly back transformer (FBT) is a second transistor It is connected to the collector terminal of (Q2).

Accordingly, the flyback transformer FBT can also supply the flyback power to the secondary side only by the on / off operation of the second transistor Q2. The second transistor Q2 is horizontally input to the base terminal. The on / off operation is performed by the state of the synchronization signal.

In constant operation, when the user adjusts the brightness of the screen, the controller M lengthens the length of the high signal applied to the base terminal of the second transistor Q2 to allow a large amount of current to flow and accordingly the flyback. The current also increases considerably on the secondary side of the transformer (FBT) side.

At this time, the third transistor Q3 receiving the voltage applied to the emitter terminal of the second transistor Q2 to the collector terminal and the base terminal is turned on in conjunction with the second transistor Q2 and accordingly resistive. Changed into ingredients.

When the third transistor Q3 maintains the on-operation state, the fourth transistor Q4 is also turned on so that the voltage applied to the third capacitor C3 through the resistor R1 is passed through the fourth transistor Q4. It is conducted to ground, and accordingly, the voltage accumulated in the third capacitor C3 is discharged.

Therefore, the internal resistance component of the variable resistive transistor PM, which varies the degree of conducting the voltage applied to the source terminal to the drain terminal according to the level of the voltage applied to the third capacitor C3, changes. When the level of the voltage applied to the capacitor C3 falls, the internal resistance of the variable resistive transistor PM increases to reduce the amount of current flowing into the error amplifier EA.

Accordingly, the error amplifier EA lowers the state of the voltage applied to the primary side of the flyback transformer FBT in response to the current flowing through the drain terminal of the variable resistive transistor PM and is then emitted from the electron gun. Reduce the amount of electrons

Provided with the image enlargement prevention circuit according to the illuminance according to the present invention as described above to prevent the large amount of electrons to be emitted even when the brightness of the screen is increased to prevent the image formed on the screen to increase and to occur in the outside of the image Suppresses spreading.

Claims (1)

Bridge diode (BD) for receiving the commercial AC power (AC) is converted to direct current and output, the smoothing first capacitor (C1) for smoothing the rectified signal output from the bridge diode (BD), and the control unit (M) The conduction of the voltage applied to the primary side by the on / off operation of the first transistor (Q1) operating by the control signal of the) is determined, and accordingly the DC voltage smoothed through the first capacitor (C1) A transformer T to be transformed and outputted to the output, a first diode D1 for preventing the voltage output to the secondary side of the transformer T from being fed back, and a second transistor operated by a state of a horizontal synchronous signal. The conduction of the voltage applied to the primary side by the on / off operation of Q2 is determined, and accordingly, the voltage output from the first diode D1 is input to the primary side to the horizontal side of the television scan to the secondary side.La del following that includes a flyback transformer (FBT) for generating power required for returning to the scanning position in the receiver rebijeon: When the second transistor Q2 is turned on, the third transistor Q3 and the third transistor Q3 act as a resistance component by interlocking and acting on the third transistor Q3. The fourth transistor Q4 which is on-operated according to the state of the voltage, the resistor R1 connecting the input terminal and the collector terminal of the fourth transistor Q4 to a predetermined positive voltage, the resistor R1 and the A third capacitor C3 formed between the connection point of the collector terminal of the fourth transistor Q4 and the ground terminal and accumulating a voltage applied through the resistor R1 during the off operation of the fourth transistor Q4; According to the level of the voltage stored in the third capacitor (C3) through the variable resistive transistor (PM) for varying the degree of conducting the voltage applied to the source terminal to the drain terminal, and through the drain terminal of the variable resistive transistor (PM) Depending on the degree of power from the flyback transformer (FBT) that is composed of the error amplifier (EA) for varying the state of the voltage across the primary winding increases, characterized in prevention image according to the illumination of the circuit.