KR19980030314A - Screen size change prevention circuit by the change of high voltage in monitor - Google Patents

Abstract

The present invention relates to a circuit for preventing the size of the screen from changing according to the change in the high voltage current (ie, the anode current).

The circuit of the present invention applies the high voltage induced in the secondary winding of the FBT to the anode, the horizontal output transistor is turned on and off in accordance with the horizontal drive signal to flow the sawtooth current through the horizontal deflection coil and the deflection coil under user control. An automatic luminance limiting circuit connected to the secondary winding of the FBT to detect a change in the anode current, the monitor being able to adjust the current flowing in the; ABL voltage detection means for monitoring a detection voltage according to a change in current of the automatic luminance limiting circuit; And a deflection current controller configured to vary a current flowing through the deflection coil through the diode modulation circuit according to the output of the ABL voltage detector.

Accordingly, the present invention prevents the CRT screen from decreasing by increasing or decreasing the current flowing through the deflection coil when the anode current changes.

Description

Circuit for prohibiting from being changed horizontal size and vertical size of picture in a monitor

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for controlling a virtual size horizontal size of a monitor, and more particularly to a circuit for preventing the size of a screen from changing due to a change in high voltage (ie, anode current).

In general, CRT beam current (i.e. anode current) varies depending on the brightness of the screen. This is a load change from the FBT point of view, the high voltage of the FBT is changed according to the change of the beam current, and the screen size is changed accordingly. In general, when the screen is dark and the beam current is small, the high pressure becomes high and accordingly, the horizontal size becomes small. On the contrary, when the screen is bright and the beam current increases, the high pressure becomes low and the horizontal size becomes large.

That is, in the CRT, the size of the screen depends on the amount of deflection (the larger the deflection amount, the larger the screen, and the smaller the deflection amount, the smaller the screen). The deflection amount is approximately expressed by the following equation (1).

Here, 'B' is the magnitude of the magnetic field, which is proportional to the product of the number of turns of the deflection coil and the current (i _dy ) flowing in the coil, Is the length of the deflection coil, and 'L' is the distance from the deflection point to the fluorescent surface. 'Va' is also the anode voltage of the receiving tube.

When the voltage of the anode is constant in Equation 1, Since L and L are fixed constants, the amount of deflection varies according to 'B', and since the number of turns of the deflection coils also has a fixed constant value, the amount of deflection is usually determined according to the current i _dy flowing in the deflection coil. Therefore, in the horizontal and vertical deflection circuits, a sawtooth current is generated and flows through this deflection coil, thereby deflecting the beam to form a screen.

However, in practice, since the voltage Va of the anode is changed, the amount of deflection changes according to the anode voltage Va. As shown in Equation 1, as the anode voltage increases, the amount of deflection decreases and thus the size of the screen. It becomes smaller, and as the anode voltage decreases, the amount of deflection increases and the screen becomes larger.

On the other hand, the voltage (high voltage) of the anode of the CRT is expressed by the following equation (2).

Here, 'Va ₀ ' is the anode voltage when the anode current is '0', 'Rs' is the internal resistance of the CRT, and 'Ia' is the anode current.

Therefore, as the current Ia of the anode increases, the voltage Va of the anode decreases, and when the voltage Va of the anode decreases, the amount of deflection increases according to Equation 1, thereby increasing the size of the screen. On the contrary, as the current Ia of the anode decreases, the voltage Va of the anode increases, and as the voltage of the anode increases, the amount of deflection decreases according to Equation 1, thereby reducing the size of the screen.

However, the anode current Ia increases when the brightness of the screen becomes bright and decreases when the screen becomes dark, so that the size of the screen changes according to the brightness of the screen. As the node current increases, the screen size increases, and when the screen darkens, the anode current decreases and the screen decreases.

Therefore, it is required to prevent the size of the screen from changing according to the brightness of the screen.

On the other hand, the circuit for adjusting the horizontal and vertical size common in the monitor is to adjust the current flowing in the deflection coil in accordance with the user's key input (user control), as shown in FIG.

Referring to FIG. 1, the horizontal output transistor Q1 is turned on and off according to the horizontal drive signal H. drive to switch the B + voltage applied through the primary winding of the FBT 130 and at the same time, a damping diode Dd. , And sawtooth current flows through the horizontal deflection coil by the action of the retrace capacitor Cr and the horizontal deflection coil Ly. At this time, the S-shaped correction capacitor Cs and the linearity correction coil (not shown) are connected to the horizontal deflection coil Ly to correct the horizontal linearity.

That is, when the deflection angle is large, the deflection angular velocity is larger than the deflection angular velocity of the center portion when scanning the peripheral portion of the screen so that the sawtooth current is S-shaped to prevent the peripheral portion of the screen from appearing longer than the center portion of the screen. Allow it to be less.

In addition, the H.size signal input from the microcomputer 170 and the pincushion adjustment signal input from the pincushion correction IC (not shown) are connected to the horizontal deflection unit 150 of the diode modulator 160. The horizontal size of the screen can be adjusted by varying the base deflection current by varying the base current of the transistor Q2.

That is, as described above, the size of the horizontal screen is determined by the amount of deflection, and the amount of deflection is changed by the current flowing through the deflection coil, so that the user can change the size of the horizontal size (H.size) by user control. When adjusted, the microcomputer 170 outputs an appropriate PWM signal to adjust the current of the horizontal deflection coil to adjust the size of the horizontal screen, and corrects the current flowing in the horizontal deflection coil according to the pincushion signal to increase or decrease the size of the screen. Keep it constant in the middle.

However, as described above, the general horizontal size adjustment is performed by adjusting the current flowing in the horizontal deflection coil Ly according to a user control or pincushion signal. The ability to adjust the size fluctuations of the problem was insignificant.

Accordingly, an object of the present invention is to provide a screen size change prevention circuit for preventing a screen size from being changed due to a change in high voltage.

In order to achieve the above object, in the circuit of the present invention, a high voltage induced in the secondary winding of the FBT is applied to the anode, and the horizontal output transistor is turned on and off in accordance with the horizontal driving signal to flow a sawtooth current through the horizontal deflection coil. And a monitor capable of adjusting a current flowing through the deflection coil according to a user control, the monitor comprising: an automatic luminance limiting circuit connected to the secondary winding of the FBT to detect a change in the anode current in order to detect a change in the anode current; And deflection current control means for varying a current flowing in the deflection coil through the diode modulation circuit in accordance with the output of the auto luminance limiting circuit.

1 is a circuit diagram showing a monitor including a conventional horizontal size adjustment circuit;

2 is a circuit diagram illustrating a monitor including a horizontal size adjustment circuit according to the present invention.

* Explanation of symbols for main parts of the drawings

110: main power supply 120: DC-DC converter

130: FBT 140: horizontal drive unit

150: horizontal output unit 160: diode modulator

170: microcomputer 180: video preamplifier

190: video power amplifier 200: deflection current control unit

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

First, the operation of the FBT will be briefly described to facilitate understanding of the present invention.

The B + voltage provided by the DC-DC converter 120 is applied to one end of the primary winding of the FBT 130, and the horizontal output unit 150 is connected to the other end thereof. In addition, there are usually a plurality of secondary windings of the FBT. Among them, there are a secondary winding for generating a high voltage, and a secondary winding for monitoring a high voltage induced in the secondary winding.

The horizontal output transistor Q1 of the horizontal output unit 150 is turned on and off by the horizontal drive signal H.drive according to the horizontal synchronous signal. When the horizontal output transistor Q1 is turned off, the high voltage is applied to the primary winding. As a result, a voltage according to the turns ratio is induced to the secondary winding, thereby obtaining a desired voltage on the secondary.

Therefore, the high voltage (HV) applied to the anode of the CRT is used by rectifying the voltage induced in the secondary winding of the FBT 130, and the high voltages (FOCUS, SCREEN) applied to the focus of the CRT and the screen grid are also applied to the secondary of the FBT. Provided in the windings. In addition, since the on / off operation of the horizontal output transistor Q1 is performed in synchronization with the horizontal synchronizing signal, the voltage pulse induced on the secondary side of the FBT is also synchronized with the horizontal synchronizing signal, so that this voltage pulse is fed back into the horizontal oscillation circuit. Sometimes used as an 'AFC pulse' used as a signal.

On the other hand, the FBT has an automatic brightness limit (ABL) circuit for controlling the brightness of the screen by monitoring the anode current.

1 and 2, when the luminance is abnormally high, the ABL circuit is a circuit for preventing a large anode current from flowing and overloading the high voltage generating circuit 130 to destroy components. To this end, the change of the anode current is detected and fed back to the brightness control voltage or contrast control voltage to perform the automatic brightness limit function. That is, when the brightness increases and the anode current exceeds the threshold, the anode current is limited by lowering the contrast control voltage of the video preamplifier 180.

Subsequently, the monitor to which the horizontal size variation preventing function is applied according to the present invention is, as shown in FIG. 2, the main power supply 110, the DC-DC converter 120, the FBT 130, the horizontal driver 140, and the horizontal output. A unit 150, a diode modulator 160, a microcomputer 170, a video preamplifier 180, a video power amplifier 190, a deflection current controller 200, and the like are provided.

In addition, the screen size prevention circuit according to the present invention detects a change in the anode current and the automatic luminance limiting circuit (R1, R2) in which the detection voltage decreases when the anode current increases and the detection voltage increases when the anode current decreases. , The deflection current control unit 200.

In addition, the deflection current controller 200 increases the voltage between the collector and the emitter when the detection voltage of the auto luminance limiting circuit decreases, and increases the voltage between the collector and the emitter when the detection voltage increases. Wow; The second transistor Q22 increases the deflection current when the output voltage of the first transistor is increased, and decreases the deflection current when the output voltage of the first transistor is decreased.

Referring to FIG. 2, the horizontal output unit 150 applies a sawtooth wave current to the horizontal deflection coil Ly by turning on and off the horizontal output transistor Q1 according to the manual drive signal H.drive. In order to correct the horizontal linearity, the linear deflection coil Ly is connected with the linearity correction coil and the S correction capacitor Cds, and a transistor Q22 for controlling the flow of the horizontal deflection current is connected thereto. .

On the other hand, according to the present invention, the ABL circuit monitors the detection voltage according to the variation of the anode current by the resistors R1 and R2, and this detection voltage (voltage at N1) becomes small as the anode current increases. And decreases as the anode current decreases.

Therefore, when the anode current increases, the detection voltage becomes small, and this detection voltage is applied to the base of the transistor Q21. When the detection voltage applied to the base of the transistor Q21 is lowered, the voltage at node 2 is increased. As the voltage at this node 2 is increased, the base voltage of transistor Q22 is increased, thereby causing the collector current of transistor Q22. As a result, the size of the deflection current is reduced by bypassing the current flowing in the horizontal deflection coil by the diode modulation circuit 160 to the transistor Q22.

In this way, when the screen becomes bright and the anode current increases, the anode voltage decreases and the size of the screen increases. In the circuit of the present invention, when the anode current increases, the ABL detection voltage decreases, and accordingly, the transistor Q21 is used. The base voltage of the transistor is lowered and thus the base voltage of the transistor is increased, thereby reducing the current flowing through the deflection coil, thereby preventing the screen size from increasing.

In contrast, when the anode current decreases, the detection voltage becomes high, and this detection voltage is applied to the base of the transistor Q21. When the detection voltage applied to the base of the transistor Q21 is high, the voltage at the node 2 is lowered. As the voltage at this node 2 is lowered, the base voltage of the transistor Q22 is lowered, thereby reducing the collector current. The circuit increases the current flowing through the horizontal deflection coil to reduce the horizontal size.

As described above, when the screen is dark and the anode current decreases, the anode voltage is increased and the screen size is reduced. In the circuit of the present invention, when the anode current is increased, the detection voltage is lowered. The voltage decreases at Q22 to increase the current flowing through the deflection coil, thereby preventing the screen from becoming smaller.

The above relationship is summarized in Table 1 below.

Screen brightness Anode current Anode voltage ABL Detection Voltage Horizontal deflection current Screen size Splashes increase decrease decrease decrease Prevent growth Darkened decrease increase increase increase Anti-small

As shown in Table 1, when the screen is brightened and the anode current increases, the anode voltage decreases, and as the anode voltage decreases, the size of the screen increases, according to the present invention. The increase is sensed by the ABL detection voltage, reducing the horizontal deflection current, thus preventing the screen from growing.

On the contrary, when the screen becomes dark and the anode current decreases, the anode voltage increases and the screen size decreases as the anode voltage increases. According to the present invention, a decrease in the anode current is detected as an ABL detection voltage. By increasing the horizontal deflection current, the screen is prevented from getting smaller.

In the embodiment of the present invention has been described in detail with respect to the technique for preventing the variation of the horizontal size around the portion associated with the horizontal deflection coil, the technical idea of the present invention is applied to the vertical deflection coil as it is to prevent the variation of the vertical screen can do.

As described above, when the brightness of the screen is changed, the size of the screen is also changed accordingly. As the screen becomes brighter and the anode current increases and accordingly the anode voltage decreases, the screen becomes larger. By reducing the current flowing through the coil to prevent the screen from becoming large, the screen is dark, the anode current is reduced, and accordingly the screen is smaller when the anode voltage is increased. According to the present invention, the screen is increased by increasing the current flowing through the deflection coil. This prevents it from becoming smaller.

Claims (3)

The high voltage induced in the secondary winding of the FBT is applied to the anode, and the horizontal output transistor is turned on and off in accordance with the horizontal drive signal, so that the sawtooth current flows through the horizontal deflection coil, and the current flowing through the deflection coil can be adjusted according to user control. A monitor, comprising: an automatic luminance limiting circuit connected to a secondary winding of the FBT to detect a change in anode current; ABL voltage detection means for monitoring a detected voltage according to a change in current of the automatic luminance limiting circuit; And a deflection current controller configured to vary a current flowing through the deflection coil through the diode modulation circuit according to the output of the ABL voltage detector. 2. The screen size change prevention circuit of claim 1, wherein the ABL voltage detecting means comprises a transistor which increases the current flowing through the collector by decreasing the base voltage when the ABL current increases. The circuit of claim 1, wherein the deflection current control means comprises a transistor configured to vary a current flowing through the deflection coil according to an output of the voltage detector.