JPH0436628B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a cathode ray tube (hereinafter referred to as CRT).
Regarding the drive circuit, it is possible to constantly stabilize the load fluctuation of the voltage supplied to the grid or cathode due to the video signal, and to adjust the brightness appropriately, and also to effectively prevent spots that occur when the power is turned off. Regarding spot killer circuits.

[Conventional technology]

Generally, in a CRT, a video output signal obtained from a video output circuit is input to the cathode K, and the first grid G
A brightness adjustment signal is input to the second grid G2, and a positive low voltage source for accelerating the electron beam emitted from the cathode K is connected to the second grid G2. In this case, the first grid G1 is maintained at a set voltage for the proper bias of the CRT by the load voltage, and controls the amount of the electron beam modulated by the video output signal input from the video output circuit to the cathode K. Reproduces images with appropriate brightness on the CRT screen.

In addition, in this type of CRT, when performing horizontal and vertical deflection of the electron beam, the return scanning line that appears during the retrace time of the sawtooth wave appears in the image and impairs the image quality, so in order to prevent this, A blanking circuit is provided. As this blanking circuit system, there are known a system in which a positive blanking pulse is applied to the cathode K, and a system in which a negative blanking pulse is applied to the first grid G1 or the second grid G2.

Furthermore, in this type of CRT, when the power switch is turned off, the power supplies to the cathode K, grids G1, G2, anode, etc. all become zero potential, but at that moment, the residual heat of the heater in the cathode K causes the electrons to A beam is generated, and due to the residual charge at the anode,
The electron beam is not scanned horizontally or vertically but is focused on the center point of the image plane,
Ions generated by colliding with the gas remaining inside the CRT tube act on the phosphor at its center, causing deterioration and alteration, so a spot killer circuit is provided to prevent this. This spot killer circuit system has a circuit configuration in which the first grid G1 is grounded via a capacitor, and the negative voltage charged in this capacitor when the power switch is turned off is used to keep the first grid G1 in a negative state for a predetermined period of time. A known method is to prevent the above-mentioned spots from occurring by holding the bias voltage at a bias voltage of 0.05 to cut off the electron beam generated by residual heat from the cathode.

[Problem that the invention seeks to solve]

However, in the above-mentioned CRT, the secondary voltage of the flyback transformer is usually suitably used as the negative voltage source for the first grid G1. However, this type of negative voltage source fluctuates due to load fluctuations, which not only causes inappropriate cutoff adjustment and degrades image quality, but also impairs the functionality of these circuits when the blanking circuit or spot killer circuit described above is employed. However, the problem is that the image cannot be fully utilized, resulting in a significant deterioration in the quality of the image. In addition, various stabilization circuits have been proposed to stabilize the negative power supply for the first grid G1, but all of them require the use of many circuit components, and therefore the circuit configuration is There are disadvantages in that it not only becomes complicated but also increases manufacturing costs.

Therefore, an object of the present invention is to have a simple circuit configuration.
Moreover, it is an object of the present invention to provide a spot killer circuit for a cathode ray tube, which can reliably stabilize the bias voltage at the first grid or cathode and properly and easily prevent electron beam spots generated when the power of the CRT is turned off.

[Means for solving problems]

The spot killer circuit for a cathode ray tube according to the present invention includes a DC voltage source that sends out a DC voltage smoothed by a capacitor in response to input of the AC voltage source, and a DC voltage supplied from the DC voltage source through a voltage drop element. In a cathode ray tube circuit configured to supply one of the cathode and the first grid, the voltage dividing circuit divides the DC voltage supplied from the voltage drop element, and the output of the voltage dividing circuit is compared with a reference voltage. a comparator circuit that controls the current flowing through the voltage drop element to supply a stabilized voltage to either the cathode or the first grid; and a voltage dividing ratio of the voltage dividing circuit in response to a signal indicating interruption of the AC voltage source. and a switch circuit that controls the current flowing through the voltage drop element by switching the voltage and stopping the comparison operation of the comparison circuit, thereby supplying a voltage to one of the cathode or the first grid to cut off the cathode ray tube. It is characterized by

[Effect]

According to the spot killer circuit for a cathode ray tube according to the present invention, when connecting to the negative voltage source of the first grid of the CRT or connecting the cathode to the positive voltage source, a voltage divider is provided to obtain the required divided voltage. , this divided voltage is applied to the base of the transistor, and a predetermined reference voltage is set at the emitter of the transistor, and the collector current of the transistor is controlled according to the voltage source to maintain the first grid voltage or the cathode at a constant voltage. . By providing a capacitor with a predetermined time constant on the voltage source side of this first grid or cathode, the power supply voltage is held for a required period when the CRT is powered off, and the base voltage of this transistor is increased toward ground. By keeping the first grid voltage or the cathode voltage below the cut-off voltage, it is possible to cut off the electron beam emitted from the cathode due to residual heat, thereby stably and reliably preventing the generation of spots.

〔Example〕

Next, an embodiment of a spot killer circuit for a cathode ray tube (CRT) according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a circuit diagram showing an embodiment of the spot killer circuit of the present invention. This embodiment shows a drive circuit for the first grid G1 of a CRT, and a negative voltage obtained on the secondary side of the flyback transformer FBT.
V ₀ is a negative voltage source, which is supplied to the first grid G1 via a diode D1 and a capacitor C1, and further via a feedback circuit FBC;
It is configured to obtain a predetermined bias voltage. The feedback circuit FBC has a resistor R1 connected between the negative voltage source and the first grid G1, and the collector of the transistor TR1 is connected between the resistor R1 and the first grid G1. The base is divided by a resistor R
2. Connect R3 to a voltage dividing circuit in which a variable resistor VR1 is connected in series. Note that the transistor TR1
The emitter is grounded via a Zener diode D2 and connected via a resistor R4 to a negative voltage source common to the resistor R1.

Feedback circuit configured like this
In the FBC, when the required output negative voltage _V0 is obtained in the flyback transformer FBT, the voltage _V1 rectified through the diode D1 is applied to the first grid G1 of the CRT through the resistor R1. Ru. However, if the load on the CRT changes and the output negative voltage _V0 of the flyback transformer FBT rises to the ground side, for example, the diode D1
The voltage V ₁ rectified by G 1 also rises, and the input voltage V ₂ of the first grid G 1 also rises.
In this case, the increased input voltage V ₂ is applied to the resistor R2,
The voltage is divided by R3 and the variable resistor VR1 and applied to the base of the transistor TR1, and as a result of this base voltage _V3 also increasing, the collector current of the transistor TR1 decreases, causing the input voltage _V2 to drop to a negative voltage. That is, depending on the increase in the input voltage _V2 , a feedback loop formed between the voltage dividing resistor R2, the variable resistor VR1, and the base-collector of the transistor TR1, and the transistor
Zener diode D2 at the emitter of TR1
By adjusting the voltage drop across the resistor R1 with the reference voltage set by , it is possible to cancel out the increase in the input voltage V ₂ and maintain the input voltage V ₂ at a constant value. Note that when the negative voltage source falls to the negative side, the operation opposite to the above is performed, and the input voltage
Always keep V ₂ constant.

A switching transistor TR2 is provided in the bias voltage stabilizing circuit for the first grid G1 of the CRT described above.
The collector of the transistor TR1 is connected via a resistor R5 to the base of the transistor TR1 constituting the feedback circuit FBC, while the emitter is grounded. Also,
The base of the transistor TR2 is connected to the negative voltage source mentioned above through a resistor R6 and grounded through a resistor R7, and a switching transistor TR3 is connected to the base through a resistor R8 to supply a blanking pulse. Connect to collector. The collector of this transistor TR3 is further connected to a positive voltage source such as a video signal or a deflection signal via a resistor R9, while its emitter is grounded. Then, a resistor R10 is connected to the base of the transistor TR3.
The circuit is configured to provide a positive blanking pulse through the .

With this circuit configuration, when no blanking pulse is input to the transistor TR3, the base voltage V ₄ of the transistor TR2 is
Since the transistor TR2 is in the off state due to the action of the negative voltage _V1 from the negative voltage source and the positive voltage _V6 on the collector side of the transistor TR3, the first grid G1 of the CRT is held at a predetermined bias voltage.
Since the capacitor C1 provided on the negative voltage source side of the first grid G1 is charged while the CRT is in operation, for example, when the power of the CRT is turned off, the electric charge charged in the capacitor C1 is transferred to the load circuit. Since the discharge takes place with the required time constant through the power supply, the voltage V ₁ can be held at a negative voltage for the required time, and since the voltage V ₆ rapidly falls towards ground when the power is turned off, the voltage V ₅ also decreases. The base voltage V ₄ of the transistor TR2 becomes a negative voltage, turning the transistor TR2 on. As a result, the collector current of the transistor TR2 increases and the base voltage _V3 of the feedback transistor TR1 increases in the direction of ground, and by increasing the bias voltage _V2 to the first grid in the negative direction, Grid G1 can be held below the cut-off voltage for a required period of time, thereby preventing the generation of spots by cutting off the electron beam generated by the cathode K due to residual heat and traveling by the remaining capacity of the anode.

In addition, during normal operation, when a blanking pulse is input to the base of transistor TR3, transistor TR3 is turned on and its collector voltage _V5 decreases, and the base voltage _V4 of transistor TR2 becomes a negative voltage, turning on this transistor TR2. state. As a result, the collector current of the transistor TR2 increases and the base voltage _V3 of the feedback transistor TR1 increases in the direction of ground, which increases the bias voltage _V2 to the first grid G1 in the negative direction and cuts it off to the CRT. It is possible to maintain the blanking voltage below the voltage and achieve the blanking function stably and reliably.

FIG. 2 shows another embodiment of the circuit of the invention,
The drive circuit for the cathode K of a CRT is shown. In other words, the circuit of this embodiment operates on the first grid G of the CRT.
A video output signal obtained from a video output circuit is input to 1, and a positive voltage source for cut-off adjustment is connected to cathode K. Therefore, in the circuit of this embodiment, the positive voltage _V0 obtained on the secondary side of the flyback transformer FBT is used as a positive voltage source, and this is applied to the cathode K via the diode D1 and the capacitor C1, and further via the feedback circuit FBC.
The structure is such that a predetermined bias voltage is obtained. Therefore, compared to the embodiment circuit shown in FIG. 1, the circuit of this embodiment has exactly the same circuit configuration, and the polarity of the polar elements is set to be opposite. In addition, in the circuit of this embodiment, the same reference numerals are given to the same components as those of the circuit shown in FIG. 1, and detailed explanation thereof will be omitted. Furthermore, the operation of the circuit of this embodiment is exactly the same as that of the circuit described above, with the only difference being the polarity of the codes handled.

〔Effect of the invention〕

As is clear from the embodiments described above, according to the present invention, the voltage obtained through the voltage divider is supplied to the base of the transistor when connected to a predetermined voltage source as a bias voltage for the first grid or cathode of the CRT. However, by setting a reference voltage at the emitter of the transistor and configuring a feedback circuit to control the collector current of the transistor to maintain the bias voltage constant when the voltage source fluctuates, the first method can be achieved with a simple circuit configuration. Stabilization of the bias voltage to the grid or cathode can be achieved.

By providing a capacitor on the voltage source side of the feedback circuit configured as described above, it is possible to reliably prevent the occurrence of spots due to the electron beam generated when the power of the CRT is turned off.

Moreover, the spot killer circuit configured in this manner has a blanking circuit at the base of the transistor of the feedback circuit that performs a switching operation to increase the base voltage toward ground when a blanking pulse is input. It is possible to easily configure a CRT drive circuit that can be used effectively.

Although preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and it goes without saying that various design changes can be made without departing from the spirit of the present invention. .

[Brief explanation of drawings]

FIG. 1 is a grid drive circuit diagram showing one embodiment of a spot killer circuit for a cathode ray tube according to the present invention, and FIG. 2 is a cathode drive circuit diagram showing another embodiment of the circuit of the present invention. K...Cathode, G1...First grid, D1
...Diode, D2...Zena diode, R
1~R10...Resistor, VR1...Variable resistor,
TR1...transistor (for feedback),
TR2...Switching transistor, TR3...
…Transistor (for blanking pulse), FBT
... Flyback transformer, C1 ... Capacitor, V ₀ ... Negative voltage (positive voltage), V ₁ ... DC rectification voltage, V ₂ ... Bias voltage, V ₃ ... Transistor
Base voltage of TR1, V ₄ ...Transistor TR2
V ₅ ... Collector voltage of transistor TR3, V ₆ ... Voltage of positive voltage source (voltage of negative voltage source).

Claims (1)

[Claims] 1. A DC voltage source that sends out a DC voltage smoothed by a capacitor in response to input of the AC voltage source, and a DC voltage supplied from the DC voltage source to the cathode or the first A cathode ray tube circuit configured to supply one side of the grid, comprising: a voltage divider circuit that divides the DC voltage supplied from the voltage drop element; and a voltage divider circuit that compares the output of the voltage divider circuit with a reference voltage to reduce the voltage of the voltage drop element. a comparison circuit that controls the current flowing through the voltage divider circuit to supply a stabilized voltage to one of the cathode or the first grid; and a comparison circuit that switches the voltage division ratio of the voltage divider circuit in response to a signal indicating cutoff of the AC voltage source. and a switch circuit that controls the current flowing through the voltage drop element by stopping the comparison operation of the circuit and supplies a voltage to cut off the cathode ray tube to either the cathode or the first grid. Pipe spot killer circuit.