JPS5911299B2 - X-ray generation prevention device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is designed to stop the generation of the high voltage when the high voltage applied to the anode of the cathode ray tube abnormally increases.
This invention relates to a device that prevents the generation of X-rays.

Hereinafter, the present invention will be explained together with a conventional device.

FIG. 1 shows a circuit according to an embodiment of the present invention, and the portion surrounded by dotted lines is the newly added portion that is characteristic of the present invention.V) The other portions are conventional circuits. First, the conventional circuit part will be explained.

Take out the flyback pulse from the winding 2 installed in the flyback transformer 1 of the color television receiver,
This is rectified by diode 3, smoothed by capacitor 4,
This rectified and smoothed output is divided by a variable resistor 5 and a resistor 6 and applied to the cathode of the Zener diode T. These 2 to 6 circuits constitute a detection circuit that detects the magnitude of the high voltage applied to the anode of the cathode ray tube. The anode of the Zener diode T is connected to the control electrode of the thyristor 8.

This thyristor 8 is inserted between the power supply terminal of the horizontal oscillation circuit and the ground. The Zener diode T becomes conductive when the output voltage of the variable resistor 5 exceeds a certain value, but it does not need to be a Zener diode and may be another switching element. Next, the operation of the conventional circuit will be explained.

Now, when the 30-color television receiver is operating normally, the change in the high voltage applied to the anode of the cathode ray tube with respect to the cathode ray tube beam current is as shown in the curve A in FIG. 2. In this state, when the high voltage applied to the anode of the cathode ray tube increases abnormally, the flyback pulse generated in the winding 2 becomes large (V) The DC voltage rectified and smoothed by the diode 3 and capacitor 4 also becomes large. Therefore, the voltage applied to the cathode of Zener diode 1 is also large v,
When this voltage raises the Zener voltage, the Zener diode 7 becomes conductive, current flows into the control electrode of the thyristor 8, and the thyristor 8 becomes conductive. As a result, the DC power supply voltage of the horizontal oscillation circuit decreases and the horizontal oscillation operation is stopped. This eliminates the generation of high voltage applied to the anode of the cathode ray tube, thereby preventing the generation of X-rays from the cathode ray tube. In this circuit, the high voltage at which the Zener diode 7 begins to conduct is higher than curve B in FIG. This curve B can be adjusted by means of a variable resistor 5, but the X-ray radiation limit line C must not be exceeded by any changes in the beam current. If curve B is kept below curve C when the beam current is large, curve B approaches curve A when the beam current is small. In this way, curve B. 5A, the high voltage may exceed curve B when the power switch is turned on, and in this case, high voltage will not be applied to the anode of the cathode ray tube even during normal operation. In order to eliminate this inconvenience, the present invention is designed so that when the beam current becomes smaller than a certain value, curve B is raised to curve D and becomes more curved than curve A.

In order to obtain such characteristics, a control circuit indicated by the dotted line in FIG. 1 was added. That is, a series circuit consisting of a resistor 9 and a switching transistor 10 is inserted between the input terminal of the Zener diode 7 and the ground, and a positive DC voltage is applied to the base of the transistor 10 from the terminal +B via the resistor 11, and the resistor 12 is connected to the base of the transistor 10. A negative voltage is applied from the terminal 13 of the flyback transformer 1 through the terminal 13 of the flyback transformer 1. 14 is a Zener diode for temperature compensation, and 15 is a power supply terminal.

A negative voltage is generated at the terminal 13 according to changes in the beam current, and the negative voltage becomes larger as the beam current becomes larger. The circuit that detects the change in beam current and obtains the DC voltage may be another circuit. When the beam current is larger than a certain value, transistor 1 is connected to the base of transistor 10.
No voltage is applied to make transistor 10 conductive, and transistor 10 is in a cut-off state. However, when the beam current becomes smaller than a certain value, the transistor 10 becomes conductive. Then,
Since the other end of the resistor 9 is grounded through the transistor 10 and the Zener diode 14, the Zener diode 7 will cease to conduct unless the output voltage of the V1 rectifier 3 becomes larger than the current voltage. That is, the control circuit using the Zener diode 7 and the thyristor 8 does not stop the operation of the high voltage generating circuit even when the voltage reaches a very high voltage, resulting in the characteristic shown by the curve D in FIG. 2. In summary, the present invention includes a detection circuit that detects an abnormal rise in high voltage applied to the anode of a cathode ray tube, and an operation of the circuit that generates the high voltage based on a detection output of a certain value or more generated by the detection circuit. a first control circuit that operates when the beam current of the cathode ray tube becomes smaller than a certain value; It is equipped with a second control circuit that controls to stop the operation of the circuit that generates the high voltage based on the value detected output, and can not only prevent the generation of X-rays but also can be used in places where the beam current is small. It does not cause malfunction.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an X-ray generation prevention device according to an embodiment of the present invention, and FIG. 2 is a characteristic diagram for explaining the device. DESCRIPTION OF SYMBOLS 1... Flyback transformer, 3... Rectifier diode, 4... Smoothing capacitor, 7... Zener diode, 8... Thyristor, 10... Transistor, 12... Resistor, 13...Terminal.

Claims (1)

[Scope of Claims] 1. A detection circuit that detects an abnormal rise in high voltage applied to the anode of a cathode ray tube, and a detection output of a certain value or more generated by the detection circuit when an abnormality in the high voltage is detected. a first control circuit that operates when the beam current of the cathode ray tube becomes smaller than a certain value; and a second control circuit that controls to stop the operation of the circuit that generates the high voltage from a detection output of a value larger than the constant value of the detection circuit. Device. 2 The detection circuit includes a rectification and smoothing circuit that rectifies and smoothes the flyback pulse, and the output voltage of the rectification and smoothing circuit is applied to the input terminal of the first control circuit, and the output voltage reaches a certain value or more. The second control circuit includes a second switching circuit that becomes conductive when the beam current reaches a certain value or less, and a second switching circuit that is connected in series with the second switching circuit. a series circuit of the second switching circuit and the resistor is connected between the input terminal of the first switching circuit and ground, so that when the second switching circuit is conductive, the first The X-ray generation prevention device according to claim 1, characterized in that the input voltage of the switching circuit is reduced.