JPS6123895Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an abnormal high voltage generation prevention circuit that prevents radiation from being emitted when the high voltage applied to the cathode ray tube of a television receiver or the like increases abnormally for some reason. In particular, the present invention relates to an abnormal high voltage generation prevention circuit that prevents malfunctions caused by high voltage circuit current.

Generally, a high voltage is applied to a cathode ray tube such as a television receiver, and when this high voltage exceeds a specified value, radiation (so-called X-rays) harmful to the human body is generated. For this reason, in television receivers and the like that require high voltage generation for the operation of the equipment, abnormal high voltage generation prevention circuits are provided in order to prevent the generation of radiation. However, as will be explained below, conventional abnormal high voltage generation prevention circuits have the disadvantage that they operate even when the voltage is lower than a specified voltage, impairing the normal operation of the equipment.

FIG. 1 is a circuit diagram showing a conventional abnormal high voltage generation prevention circuit, in which a flyback transformer 1 whose primary winding 2 is supplied with horizontal output pulses has a high voltage rectifier diode at one end of its secondary winding 3. A high voltage is supplied to the anode of the cathode ray tube 5 through the tertiary winding 4, and one end of the tertiary winding 6 is grounded and the other end is connected to a rectifier circuit formed by a diode 7 and a capacitor 8.
A series circuit consisting of resistors 9 and 10 is connected in parallel with the capacitor 8, and a connection point between the resistors 9 and 10 supplies a bias potential to the emitter of the transistor _Q1 . A resistor 11 is connected between the base of the transistor _Q1 and the diode 7, and a Zener diode 12 and a resistor 13 are connected between the base of the transistor _Q1 and the reference potential.
A series circuit is connected to the resistor 13, and a capacitor 14 is connected in parallel to the resistor 13. the transistor
The collector of Q ₁ is connected to the reference potential via a resistor 15, and a change in the terminal voltage of the resistor 15 operates a switching circuit 16.
The switching action stops the oscillation of the horizontal oscillation circuit 40 and suppresses the generation of abnormally high voltage. The other end of the secondary winding 3 of the flyback transformer 1 is connected to a reference potential via a capacitor 17, and a resistor 18 is connected between one end of the capacitor 17 and one end of the resistor 13. There is. Furthermore, a resistor 20 is connected between one end of the secondary winding 3 and the video circuit 19.
21 and 22 series circuits are connected. Furthermore, a resistor 23 is connected between the connection point of resistors 20 and 21 and the power supply _E2 .
However, a diode 24 is connected between the connection point of the resistors 21 and 22 and the power source _E1 .

In the conventional abnormal high voltage generation prevention circuit configured as described above, when abnormal high voltage is generated for some reason, this abnormal high voltage is detected by the tertiary winding 6 and is detected by the diode 7 and capacitor 8. The rectified voltage is applied to the cathode side of diode 7 as voltage E _A
appears as a resistor 9, which divides this voltage E _A ,
The potential E _B at the connection point of 10 is Zener diode 1
When the voltage becomes higher than the sum of the Zener voltage of 2 and the terminal voltage _E of the resistor 13, the transistor _Q1 becomes conductive, and current flows through the resistor 15.
The switching circuit 16 is driven by the voltage generated in the horizontal oscillation circuit 40, and the horizontal oscillation in the horizontal oscillation circuit 40 is stopped, and the generation of pulses contributing to the generation of high voltage is stopped, thereby suppressing the generation of abnormally high voltage.

Further, the potential E _C on the anode side of the Zener diode 12 is used for automatic brightness limiting. That is, until the transistor Q ₁ becomes conductive, the anode voltage E _C of the Zener diode 12 decreases monotonically as shown in the characteristic curve of FIG. 2, but when the beam current of the cathode ray tube 5 exceeds Ia ₁ When ₁ becomes conductive, it decreases rapidly. As a result, the voltage applied to the anode of the diode 24 also decreases rapidly and the diode 24 is cut off. Due to this cut-off, the resistor 21 is disconnected from the power source _E1 , and its effective impedance becomes large. In this way, by blocking the diode 24, the impedance on the input end side of the video circuit 19 increases, the beam current is limited, and the ABL operation is performed. In this way, the ABL operation is performed to prevent the generation of abnormal high voltage, but since the larger the beam current, the lower the generated voltage, the detection of abnormal high voltage is done to prevent the generation of radiation. As described above, the beam current is detected using the characteristics shown in the characteristic curve of FIG.

As shown in Figure 2, this conventional abnormal high voltage generation prevention circuit operates normally until the beam current reaches Ia ₂ , but when the beam current exceeds Ia ₂ , the voltage detected as an abnormal high voltage is due to ABL operation. Even if the detection voltage is lower than the detected voltage of As the oscillation stops, the high voltage generation function is lost and the receiver stops functioning. At this time, if the power to the receiver is cut off and then turned on again, the beam current will operate normally with a value smaller than Ia ₂ .

As described above, in the conventional abnormal high voltage generation prevention circuit, its detection voltage drops rapidly when the beam current value exceeds Ia ₁ , and malfunctions occur when it falls below the ABL operating voltage. As a result, if the beam current changes during brightness adjustment, problems such as unnecessarily stopping horizontal oscillation occur.

The present invention solves the above-mentioned difficulties, and even when the beam current is changed due to brightness adjustment, etc., the detection voltage for abnormally high voltage generation is set appropriately, and the abnormality due to brightness adjustment (change in beam current) is set appropriately. The purpose is to prevent malfunction of high voltage generation prevention.

Hereinafter, typical embodiments of the present invention will be described with reference to the drawings.

FIG. 3 is a circuit diagram showing a typical embodiment of the present invention, and the same parts as in FIG. 1 are given the same reference numerals, and the explanation of their operation will be omitted. Anode of Zener diode 12 and capacitor 17
Resistors 25 and 26 are connected in series between one end of the
A series circuit of a diode 27 and a resistor 28 is interposed and connected between the connection point of the resistors 25 and 26 and the reference potential.

Now, considering the case where the beam current increases,
As explained in FIG. 2, as the beam current increases, the terminal voltage E _C of the resistor 13 connected to the anode of the Zener diode 12 decreases as shown by the characteristic curve in FIG. 4. As the beam current increases, when the beam current is Ia ₁ , the transistor Q ₁ becomes conductive as described above and in the conventional example. As shown in the characteristic curve in Figure 4, the detection voltage E _C used for ABL operation suddenly decreases when the beam current increases from Ia ₁ due to the conduction of transistor Q ₁ , but as the beam current increases further and reaches Ia ₂ . Then, the diode 27 becomes conductive. Due to the conduction of this diode 27, the resistor 28 is connected between the connection point of the resistors 25 and 26 and the reference potential, so that the transistor Q ₁ is connected from the resistors 25 and 26
Prevents the impedance from decreasing when viewed from the side. Therefore, when the beam current increases to Ia ₂ , the diode 27 becomes conductive, and as shown in the characteristic curve in Figure 4, even if the beam current increases beyond Ia ₂ , the detection voltage E _C used for ABL operation remains constant. To compensate for the sudden decline,
It is possible to prevent malfunction of the abnormal high voltage generation prevention operation due to an excessive decrease in the detection voltage of the ABL voltage. That is, this prevents a malfunction in which the abnormally high voltage generation operation excessively precedes the ABL operation and unnecessarily stops the operation of the receiver. Incidentally, in FIG. 4, the slope of the characteristic curve in the region exceeding the beam current Ia ₂ can be arbitrarily changed within the region indicated by two broken lines in the figure by changing the value of the resistor 28.

FIG. 5 is a diagram showing another typical embodiment of the present invention, in which parts having the same circuit configuration as in FIG. 3 are given the same reference numerals, and their explanation will be omitted.

As mentioned above, when the beam current increases, the transistor Q ₁ conducts and the detection voltage E _C for ABL operation increases.
decreases. As the detection voltage E _C decreases, the detection voltage for preventing abnormal voltage generation also decreases, causing the horizontal oscillation circuit 40 to stop operating unnecessarily, thereby impeding the normal functioning of the receiver. In this embodiment, resistors 29 and 30 are connected between the anode of the Zener diode 12 and one end of the capacitor 17, and a resistor 29 is connected between the anode of the Zener diode 12 and one end of the capacitor 17.
A diode 31 is connected in parallel with the resistors 29 and 30 so that its cathode side is connected to the connection point between the resistors 29 and 30. By having such a circuit configuration, the diode 31, which is normally in a conductive state, will be able to operate when the beam current increases and reaches Ia ₂ (when the beam current reaches Ia ₂ in Fig. 4). The diode 31 becomes reverse biased and shut off. By cutting off the diode 31, the impedance seen from one end of the capacitor 17 toward the transistor _Q1 increases, and the beam current flowing into the cathode ray tube 5 through the resistor 30 decreases. As a result, the fourth
The characteristics shown in the characteristic curve in the figure, that is, even when the beam current increases, the detection voltage used for ABL operation is prevented from dropping excessively, and the unnecessary abnormal high voltage generation prevention operation is not performed. This prevents the operation of the horizontal oscillation circuit 40 from being stopped inadvertently. Note that in FIGS. 3 and 5, the ABL operation is performed by switching the diode 24.

As described above, in the present invention, the detection voltage for ABL operation that conventionally occurs decreases as the beam current increases, so that the abnormal high voltage generation prevention circuit operates in advance of ABL operation. This makes it possible to reliably prevent malfunctions in which the horizontal oscillation circuit is stopped unnecessarily. Therefore, it is possible to reliably achieve both the abnormal high voltage generation prevention effect of controlling the horizontal oscillation circuit operation by the switching circuit and the ABL operation of controlling the amount of beam current.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a conventional abnormal high voltage generation prevention circuit, Fig. 2 is a characteristic diagram for explaining the circuit of Fig. 1, and Figs. 3 and 5 each show an embodiment of the present invention. The circuit diagram and FIG. 4 are characteristic diagrams for explaining the operation of the present invention. 1... Flyback transformer, 3... Secondary winding (output), 5... Cathode ray tube, 6... Tertiary winding (detection), 9, 10... Resistor for voltage divider circuit, Q ₁ ... Transistor, 12, 13, 14... Zener diode, resistor, capacitor constituting the bias circuit, 15... Load resistor, 16... First switching circuit, 19... Video circuit, 25, 29...
First impedance resistor, 26, 30... Second impedance resistor, 20, 21, 22,
23, 24... automatic brightness limiting circuit, 27, 28,
31...Second switching circuit.

Claims (1)

[Scope of Claim for Utility Model Registration] A detection winding of a flyback transformer that generates a voltage according to the amount of beam current of a cathode ray tube, a voltage divider circuit that divides the detection voltage obtained by the detection winding, and this component. a transistor whose conduction is controlled according to the divided voltage of the voltage circuit; and a transistor which is interposed between the load of this transistor and the horizontal oscillation circuit, and switches in response to the conduction of the transistor to stop the oscillation operation of the horizontal oscillation circuit. a first switching circuit configured to prevent abnormally high voltage from occurring; and a first switching circuit connected in series between the bias circuit of the transistor and the output winding of the flyback transformer.
and a second resistor; and an automatic brightness limiting circuit that is connected to the first resistor and the input side of the video circuit and controls the amount of beam current by changing the impedance on the input side of the video circuit in accordance with potential fluctuations of the bias circuit. , at least a switching diode, which has one end connected to the connection point of the first resistor and the second resistor and the other end connected to a predetermined potential point, and which effectively changes the total impedance value of the first and second resistors. What is claimed is: 1. An abnormal high voltage generation prevention circuit comprising: a second switching circuit having a second switching circuit;