JPH0436629B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a cathode ray tube (hereinafter referred to as CRT).
Blanking that can constantly stabilize the drive circuit and perform appropriate brightness adjustment and achieve stable blanking, especially in response to load fluctuations in the voltage supplied to the grid or cathode due to video signals. Regarding 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 of an appropriate bias for the CRT by a negative voltage source, 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 two known methods: one in which a positive blanking pulse is applied to the cathode K, and the other 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 blanking circuit for a cathode ray tube that can reliably stabilize the bias voltage at the first grid or cathode and can appropriately and easily perform blanking based on the input of a blanking pulse.

[Means for solving problems]

A cathode ray tube blanking circuit according to the present invention is a cathode ray tube configured to rectify and smooth a flyback pulse and supply a DC voltage obtained to the cathode or the first grid via a voltage drop element. The circuit includes: 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 control the current flowing through the voltage drop element and connect the cathode or the first a comparator circuit that supplies a stabilizing voltage to one side of the grid; and a current that flows through the voltage drop element by switching the voltage division ratio of the voltage divider circuit in response to application of a blanking pulse and stopping the comparison operation of the comparator circuit. and a switch circuit for controlling the voltage and supplying a voltage for cutting off the cathode ray tube to either the cathode or the first grid.

[Effect]

According to the cathode ray tube blanking circuit according to the present invention, when the first grid of the CRT is connected to a negative voltage source or the cathode is connected to a 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 fluctuations in the voltage source. The first grid voltage or cathode is always maintained at a constant voltage. Then, when a blanking pulse is input to the base of this transistor, the base voltage is increased toward ground, and the first grid voltage or cathode voltage is maintained below the cutoff voltage, so that blanking can be achieved stably and reliably. .

〔Example〕

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

FIG. 1 is a circuit diagram showing an embodiment of the blanking circuit of the present invention. This embodiment shows a drive circuit for the first grid G1 of a CRT, in which a negative voltage _V0 obtained on the secondary side of a flyback transformer FBT is used as a negative voltage source, and this is further fed back through a diode D1 and a capacitor C1. circuit
The voltage is supplied to the first grid G1 via the FBC 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 resistor R2, R
3 is connected to a voltage dividing circuit in which a variable resistor VR1 is connected in series. The emitter of the transistor TR1 is grounded via a Zener diode D2 and connected to a negative voltage source common to the resistor R1 via a resistor R4.

Feedback circuit configured like this
In 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 resistor R2,
The voltage is divided by R3 and the variable resistor VR1 and applied to the base of the transistor TR1, and this base voltage _V3 also increases, so that the collector current of the transistor TR1 decreases and the input voltage _V2 falls 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 R1, the increase in the input voltage _V2 can be offset, and the input voltage _V2 can always be maintained 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.

Then the blanking pulse
When input to the base of TR3, transistor TR
3 turns on, its collector voltage V ₅ drops, and 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 transistor TR2 increases and the feedback transistor TR2 increases.
The base voltage V ₃ of the first grid G 1 increases toward ground, and the bias voltage V ₂ to the first grid G 1 increases in the negative direction to keep it below the cut-off voltage of the CRT;
The blanking action can be achieved stably and reliably.

In addition, in the circuit of this embodiment, the first grid G
The capacitor C1 provided on the negative voltage source side of 1 is
Since the CRT is charged while the CRT is in operation, for example, when the CRT power is turned off, the electric charge charged in the capacitor C1 is discharged at the required time constant via the load circuit. G1 can be held at a negative voltage for the required time, thereby cutting off the electron beam generated by the residual heat of the cathode K and traveling by the remaining capacity of the anode, thereby preventing the generation of spots.

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 is connected 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. For this reason, in this example circuit, the example circuit shown in FIG. 1 is compared, and the circuit configuration is exactly the same, 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 symbols 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.

For the feedback circuit configured in this manner, by providing a circuit at the base of the transistor that performs a switching operation so as to increase the base voltage toward the ground when a blanking pulse is input, the feedback circuit can be operated in conjunction with the operation of the feedback circuit. Thus, proper blanking can be achieved reliably.

Furthermore, in this case, by providing a capacitor for the voltage source that supplies the bias voltage for the first grid or cathode of the CRT, it is possible to easily prevent the occurrence of spots on the image screen when the power of the CRT is turned off.

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 the blanking circuit for a cathode ray tube according to the present invention;
The figure 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)

[Scope of Claims] 1. In a cathode ray tube circuit configured to supply a DC voltage obtained by rectifying and smoothing a flyback pulse to either a cathode or a first grid via a voltage drop element, the voltage drop a voltage divider circuit that divides the DC voltage supplied from the element; and a voltage divider circuit that compares the output of the voltage divider circuit with a reference voltage to control the current flowing through the voltage drop element and stabilize it at one of the cathode or the first grid. a comparator circuit that supplies a voltage; and a voltage divider ratio of the voltage divider circuit that is switched in response to application of a blanking pulse to stop the comparison operation of the comparator circuit, thereby controlling the current flowing through the voltage drop element and supplying the voltage to the cathode. Alternatively, a blanking circuit for a cathode ray tube characterized in that one of the first grids is provided with a switch circuit for supplying a voltage to cut off the cathode ray tube.