KR920000910Y1 - Beam current limmited circuit for cathod ray tube - Google Patents

Abstract

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Description

Beam current limiting circuit of cathode ray tube

1 is a conventional circuit diagram.

2 is a circuit diagram of the present invention.

* Explanation of symbols for the main parts of the drawings

110: video driver 130: CRT

140: water output unit 150: FBT

160: video bias supply unit Q1, Q2: transistor

D1, D3, D4: Diode D4: Zener Diode

R1-R4: resistors C1, C2: capacitors

The present invention relates to a circuit for controlling the simultaneous beam current of the blanking operation during beam scanning in an image display device having a cathode ray tube (hereinafter referred to as a CRT).

In general, it is widely used for a monitor such as a television and a large or personal computer, and the image display device uses a lot of CRT.

In the conventional image display apparatus, the video amplifier 100, the video driver 110, the video output unit 120, the CRT 130, the horizontal output unit 1 40, and the flyback as shown in FIG. Fly Back Trans (hereinafter referred to as FBT) 150, the video bias supply unit 160, the resistor and capacitor (R1,) for controlling the video bias supply unit 160 in accordance with the secondary voltage state of the FBT (150) C1) a voltage divider.

Referring to the operation of FIG. 1, the voltage divider consisting of the resistor R1 and the capacitor C1 charges and discharges the capacitor C1 according to the voltage level of the secondary side of the FBT 150, wherein the resistor R2 and the transistor Q1 are operated. The bias supply unit 160 including the zener diode D1 and the blanking diode D1 supplies the bias voltage VZ to the video supply unit 110 according to the charging voltage of the capacitor C1.

In addition, the FBT 150 supplies the horizontal deflection voltage gradually increasing by the sawtooth wave-shaped horizontal deflection signal supplied from the horizontal output unit 140 to the horizontal deflection coil of the CRT 130. Referring to the operation of Figure 1 in more detail as follows.

The BEAM current of the CRT is the current due to the energy accumulated in the coil COIL of the FBT 150 by the current i1 flowing in the direction of the arrow shown in the drawing of Fig. <1> and the horizontal deflection signal of the horizontal output unit 140. Separated by.

When the current of the horizontal deflection signal increases, both the current i1 in the direction of the arrow and the current due to the energy accumulated in the FBT 150 increase proportionally.

As the voltage on the secondary side of the FBT 150 increases when the voltage level of the horizontal deflection signal, which is the output of the horizontal output unit 140, increases gradually, the current in the arrow direction i1 also decreases so that the voltage drop due to R1 decreases. Relatively, the charging voltage of the capacitor C1, that is, the potential of the connection point (a) is higher than the potential of the connection point (c), which is the anode of the diode D1, so that the transistor Q1 and the diode D1 are turned off. The bias voltage supplied to the driver 110 becomes the voltage VZ by the zener diode D2.

During the retrace period during which the voltage level of the horizontal deflection signal, which is the output of the horizontal output unit 140, decreases rapidly, as the secondary voltage of the FBT 150 decreases rapidly, the voltage drop caused by the resistor R1 increases to increase the voltage of the capacitor C1. As the charging voltage voltage, i.e., the voltage on the connection point (a) decreases, the base potential of the transistor (Q1) becomes lower than the emitter potential, so that the transistor and the diode (D1) are turned on (ON) so that the voltage at the connection point (b) is the zener diode (D2). The reference power supply (GND) lower than the voltage VZ is applied, and the reference potential (GND) is supplied to the bias voltage of the video drive stage to lower the video output gain to control the beam current to a predetermined value or less. It prevents damage and burning of the phosphor in the CRT 130.

However, in FIG. 1, the current in the direction of the arrow also increases when switching between syringes to the return period, so that the potential at the junction point (A) decreases, but the high voltage charged in C1 during normal operation (when the BEAM current flows less) causes the FBT (150). Since the electric current caused by the energy induced on the secondary side of the cell does not discharge immediately, the voltage at the connection point (b) does not become a voltage at which the transistor Q1 can be turned on. Therefore, since the response speed of the circuit is slow, many beam currents flow through the CRT 130 before the transistor Q1 is turned on to burn the phosphor PPHOSPHOR of the CRT 130 or damage the electron gun.

Accordingly, an object of the present invention is to provide a limiting circuit of a cathode ray tube that can improve a response speed for limiting a beam current to a change in a horizontal deflection voltage supplied to a deflection coil of a CRT in an image display device.

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

2 is a circuit diagram of the present invention, an image display device having a video amplifier 100 and a video driver 110, a video output unit 120, a CRT 130, a horizontal output unit 140, and an FBT 150. The video bias supply unit 160 is connected to the secondary side of the FBT 150 through a line 1 and supplies a bias voltage to the video driver 110 according to the secondary side potential of the FBT 150. A resistor R1 connected between a supply power source B + and the line 1, a capacitor C1 connected between the line 1 and a connection point 2, the connection contact 2 and a reference power source. A discharge consisting of a resistor (R3) and a transistor (Q2) connected between a diode (D3) connected between (GND) and the line (1) and a connection point (2) to provide a discharge passage of the capacitor (C1). A resistor R4 and a capacitor C2 are connected in parallel to the passage means and the diode D3 to prevent damage to the diode D3 and the discharge passage means. Constitute a Robo call means.

Therefore, the present invention will be described in detail with reference to FIG. The hydraulic output unit 140, the FBT 150, the CRT 130, the video amplification unit 100, the video driver 110, the video output unit 120, the configuration of anyone skilled in the art can know The construction is well known and the detailed description is weak.

The details of the video bias supply unit 160 are the same as those described in FIG.

At the time of scanning time when the voltage level of the horizontal deflection signal, which is the output of the horizontal output unit 140, gradually increases, as the secondary voltage of the FBT 150 increases, the arrow direction current decreases and the voltage drop caused by the resistor R1 decreases. The transistor Q1 and the diode D1 are turned off because the potential on the line 2 is higher than the potential at the connection point C. At this time, the bias voltage supplied to the video driver 110 is a voltage generated by the zener diode D2. VZ).

During the key line period in which the voltage level of the horizontal deflection signal, which is the output of the horizontal output unit 140, decreases rapidly, the secondary voltage of the FBT 150 decreases rapidly, so that the current in the direction of the arrow also increases to lower the potential on the line 1. The transistor Q1 and the diode D1 are turned on and the potential on the connection point I is lower than the voltage VZ by the zener diode D2 so that the reference potential GND is the bias voltage of the video driver 110. Is supplied.

When the bias voltage of the video driver 110 is lowered, the output gain GAIN of the video outputter 120 is lowered to automatically limit the beam current to protect the CRT 130.

When switching from the syringe to the return period, due to the charging voltage charged at both ends of the capacitor C1 between the syringes, the connection point (2) has a negative (-) voltage and the diode (D3) is turned off and the transistor ( The negative (-) voltage of the emitter of Q2 is applied, and as the transistor Q2 conducts, the high voltage charged during the syringe period is discharged immediately. As soon as the syringe is switched to the return period, the bias voltage of the video driver 110 can be lowered to limit the speed at which the beam current is high.

As described above, the present invention has the advantage of preventing the burning of the phosphor of the CRT or the damage of the electron gun by limiting the beam current by immediately blocking the bias voltage supplied to the video driver at the moment of switching from the syringe to the return period. By blocking the bias voltage of the video driver with respect to the horizontal deflection signal of the output, there is an advantage that can improve the response speed limiting the beam current.

Claims (1)

In the image display device including the video amplifier 100 and the video driver 110, the video output unit 120, the CRT 130, the horizontal output unit 140, the FBT 150, the FBT 150 A video bias supply unit 160 connected to a secondary side and a line 1 to supply a bias voltage to the video driver 110 according to the secondary side potential of the FBT 150, a power supply B + and the line. A resistor R1 connected between (1), a capacitor C1 connected between the line 1 and a connection point 2, and a diode connected between the connection point 2 and a reference power supply GND ( D3) and discharge passage means connected between the line 1 and the connection point 2 to provide a discharge passage of the capacitor C1, and connected in parallel with the diode D3 to connect the diode D3 and the discharge passage. A cathode ray tube beam current limiting circuit, comprising: circuit protection means for preventing damage to the furnace means.