JPH07327144A - X-ray generation prevention circuit for video equipment - Google Patents

Abstract

PURPOSE:To prevent production of an X-ray by interrupting an AC power switch based on a fault discrimination of a high frequency transformer output voltage by a level discrimination means so as to stop the operation of a high frequency transformer surely. CONSTITUTION:A high frequency output current at a terminal 7x of a secondary winding of a high frequency transformer 7 is rectified and given to an X-ray protection circuit 22 via a point P. The input voltage is monitored and when it exceeds a prescribed voltage, an oscillation stop signal is fed to a horizontal oscillation circuit 5. On the other hand, a level discrimination means of a CPU 10 detects a voltage received by an X-ray protection input port 10x to discriminate the threshold level. If the voltage is higher than a prescribed threshold value, it is discriminated that an abnormal voltage is generated and the CPU 10 provides an output of a signal to switch off a power switch to the X-ray protection output port 10y. An OFF circuit 14 goes to an L level based on a level output and an electromagnetic relay 13 is driven to interrupt the AC power input switch 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray generation prevention circuit for a video device, for example, an X-ray generation prevention circuit for a television receiver, a monitor device or the like as a video device.

[0002]

2. Description of the Related Art Cathode ray tubes for television receivers (hereinafter referred to as CR
In a video device using a T.T.), there is a risk that X-rays are rapidly and strongly generated as the anode voltage applied to the CRT gradually increases. That is, an electron beam is accelerated by a high anode voltage and generates an X-ray when it collides with an anode electrode. Such an X-ray has a sharp increase in the X-ray intensity as the anode voltage increases. , If the strength exceeds a predetermined value, it will be harmful to the body, so it has a great effect on infants and young children. For this reason, it is indispensable to equip a video device using a CRT such as a television receiver with an X-ray generation prevention circuit.

The cause of the abnormal rise of the anode voltage applied to the CRT is the rise of the supply voltage to the primary winding of the high frequency transformer due to the abnormality of the resonance capacitor of the horizontal oscillation circuit or the short circuit between the windings of the high frequency transformer. There is an abnormal occurrence such as. Due to such a cause, the anode voltage is abnormally increased.

On the other hand, the conventional X-ray generation prevention circuit is
The horizontal oscillation circuit is stopped when an abnormal rise in the secondary voltage of the high frequency transformer is detected. A conventional X-ray generation prevention circuit applied to a television receiver will be described with reference to FIG. In FIG. 3, reference numeral 2 is an AC power supply input switch, 3 is a rectifier circuit, 4 is a power supply circuit (+ B power supply) that stabilizes DC voltage, 5 is a horizontal oscillation circuit, and 6 is an oscillation signal of the horizontal oscillation circuit 5. A horizontal oscillation drive circuit which receives the power supply from the power supply circuit 4 and outputs an oscillation signal with an increased amplitude. A high frequency transformer 7 has a high frequency current of the horizontal oscillation drive circuit 6 in a primary winding (coil) L1 thereof. Enter multiple 2
A high frequency current is generated on the side of the next winding (coil) L2. 8
Is a DC stabilized power source for rectifying the output high frequency current to obtain a predetermined stable DC voltage, and 9 is a voltage stabilizing integrated circuit thereof. These DC stabilized power supplies 8 are supplied to drive the electronic circuits of the television receiver. Reference numeral 10 denotes a CPU for controlling the system of the entire television receiver, which is operated by the backup circuit 11 even when the AC power input switch 2 is off. A command to turn on the television receiver is detected from the key input section, an "H" level signal is output to the P-ON port, the transistor 12 is turned on, the electromagnetic relay 13 is driven, and the AC power input switch 2 is turned on. Operate the TV receiver. Reference numeral 20 denotes a CRT, which directly rectifies the high frequency output of the secondary winding of the high frequency transformer 7 and supplies it to the respective electrodes of the anode, focus and screen. The cathode electrode is connected via an automatic brightness limiting circuit (ABL) 21. 22 is an X-ray protection circuit. The high frequency output of the secondary winding output terminal 7x of the high frequency transformer 7 is converted into a direct current by the diode Dx and the capacitor Cx, and this voltage is monitored by the input terminal 22x of the X-ray protection circuit 22. The horizontal oscillation stop signal is output from the output terminal 22y on the assumption that the high frequency voltage of the next winding exceeds the predetermined value. The horizontal oscillation circuit 5 inputs this signal to the input terminal 5x.
Input to stop horizontal oscillation. Therefore, the high frequency does not have the high frequency current component of the primary winding of the transformer 7, and the output of the secondary winding becomes zero. Therefore, the operation of the CRT 20 is stopped.

[0005]

However, it has been difficult to reliably prevent the generation of X-rays from the CRT 20 with such a conventional X-ray generation preventing circuit configuration. That is, for example, if the horizontal oscillation circuit 5, the horizontal oscillation drive circuit 6 or the like is in the self-excited oscillation state due to an abnormality including the high frequency transformer 7 and the electronic circuits in the vicinity thereof, the X-ray protection circuit 2
Even if 2 outputs the horizontal oscillation stop signal, the high-frequency transformer 7 may continue to maintain the boosted state, and there is a possibility that high-intensity X-rays may continue to be generated.

The present invention has been made in order to solve the problems and drawbacks of such a conventional structure, and its purpose is CR.
It is an object of the present invention to provide an X-ray generation prevention circuit for a video device configured to surely stop the operation of the high frequency transformer when a voltage higher than a specified value is supplied to the anode of T.

[0007]

In order to achieve the above object, an X-ray generation prevention circuit of a video device according to the present invention detects a secondary winding voltage of a high frequency transformer and determines a predetermined X-ray intensity based on the detection signal. It is characterized by further comprising a level determination means for determining whether or not the value is exceeded, and a control section for turning on / off the power supply of the video device according to the level determined by the level determination means.

[0008]

The X-ray generation preventing circuit of the video device according to the present invention is
The secondary winding high frequency voltage is converted into a direct current, the direct current voltage is divided by a voltage dividing circuit at a predetermined ratio, and the divided voltage value is input to the X-ray protection input port of the control unit. Here, if the voltage division ratio is selected and set so that the lowest value judged to be abnormal X-ray intensity can be used as the threshold value, abnormal X-ray intensity can be immediately judged at the X-ray protection input port. When the level determination means determines that the output voltage of the high frequency transformer is abnormal as described above, the control section outputs a power switch switching signal from the X-ray protection output port to shut off the power based on the determination result. By switching the power switch, the supply of energy to the high frequency transformer is cut off, so that the high frequency transformer surely stops operating. As a result, the voltage supply to the anode of the CRT is surely stopped, so that the generation of X-rays from the CRT is surely stopped.

[0009]

Embodiments of the present invention will be described below with reference to the accompanying drawings. First, the structure of the present invention will be described. FIG. 1 shows an X according to the present invention applied to a television receiver as a video device.
It is a block block diagram of the Example of a line generation prevention circuit.

Referring to FIG. 1, which is a block diagram of an X-ray generation prevention circuit according to the present invention applied to a television receiver. In FIG. 1, the same reference numerals as those in FIG. 3 are omitted.
The high frequency current output from one output terminal 7x of the secondary winding of the high frequency transformer 7 is a diode Dx and a capacitor C.
X-ray protection circuit 2 that is rectified by x and passes through the connection points P
It is connected to the second input terminal 22x, but is also connected to the X-ray protection input port 10x of the CPU 10 (control unit) from the point P. However, the voltage is divided by the resistors Rx and Ry and input to the input port 10x. The CPU 10 has an X-ray protection output port 10y. P- of CPU 10
The output lines of the ON output port and the X-ray protection output port 10y are connected via the AND circuit 14 to the output terminal of the transistor 1
Connected to 2. It is P-ON that the electromagnetic relay 13 is driven and the AC power input switch 2 is turned on (closed state).
It is only when the terminal and the 10y terminal simultaneously become "H" level.

Next, the operation will be described. High frequency transformer 7
The high frequency output current of the 7x terminal, which is one of the secondary windings, is rectified by the diode Dx and the capacitor Cx and input to the 22x terminal of the X-ray protection circuit 22 via the point P. This input voltage is monitored, and if it exceeds a predetermined value, the horizontal oscillation circuit 5
The sending of the oscillation stop signal to the input terminal 5x of is carried out as usual. Further, the data is input to the X-ray protection input port 10x of the CPU 10 via the point P via the resistor Rx. The DC voltage from point P is divided by resistors Rx and Ry. The divided voltage value is the minimum limit value at which the high-frequency voltage generated at the output terminal 7x of the high-frequency transformer 7 increases from the reference value and the generated X-ray is judged to be abnormal. The values of the resistors Rx and Ry are selected so that the "level" can be determined. Since the resistors Rx and Ry are set as described above, the CPU 10 monitors the increase of the high frequency transformer 7 from the reference value in real time at the X-ray protection input port 10x.

FIG. 2 is an operation flowchart of the CPU 10 (control unit) in FIG. The level determination means of the CPU 10 detects the voltage input to the X-ray protection input port 10x, determines the threshold value, and compares and determines whether the threshold value is greater than a predetermined value (steps S1 and S2). If it is less than or equal to a predetermined threshold value, it is determined to be normal. If it is larger than a predetermined threshold value, it is determined that an abnormal voltage has occurred, and the CPU
10 outputs a signal for turning off the power switch to the X-ray protection output port 10y based on this determination result.

Based on this, a predetermined level (for example, L level) is output to the X-ray protection output port 10y (step S3). Based on this level output, the output of the OFF circuit 14 becomes L level, the electromagnetic relay 13 is driven, the AC power supply input switch 2 is cut off, and the + B power supply to the high frequency transformer 7 is cut off. As a result, the voltage supply to the anode of the CRT 20 is stopped, the operation of the CRT 20 is stopped, and the generation of X-rays disappears.

[0014]

As described above, in the X-ray generation prevention circuit of the video apparatus according to the present invention, the control unit performs a predetermined output based on the abnormality determination of the high frequency transformer output voltage by the level determination means, and this output On the basis of the above, the AC power input switch is cut off, the power supply to the transformer is cut off, and the energy supply to the high frequency transformer is cut off, so that the high frequency transformer can be reliably stopped.

As a result, the voltage supply to the anode of the CRT can be surely stopped, so that the X-ray generation from the CRT can be surely stopped. As described above, according to the present invention, it is possible to reliably prevent the generation of X-rays without using a special component or a special circuit.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of an embodiment of an X-ray generation prevention circuit according to the present invention applied to a television receiver.

FIG. 2 is an operation flowchart of a CPU shown in FIG.

FIG. 3 is a block configuration diagram of a conventional X-ray generation prevention circuit applied to a television receiver.

[Explanation of symbols]

 2 AC power input switch 3 Rectifier circuit 4 Power supply circuit 5 Horizontal oscillation circuit 6 Horizontal oscillation drive circuit 7 High frequency transformer 10 CPU (control unit, level determination means) 20 CRT 22 X-ray protection circuit Rx, Ry voltage dividing resistors (voltage dividing circuit) )

Claims (1)

[Claims] 1. A level determination unit that detects a secondary winding voltage of a high frequency transformer and determines whether or not a predetermined value of X-ray intensity is exceeded by the detection signal, and the level determined by the level determination unit. Turn on / off the video device
An X-ray generation prevention circuit for a video device, comprising a control unit for turning off.