JPS6035869B2 - X-ray protection device - Google Patents

Description

[Detailed description of the invention] This invention relates to an X-ray protection device.

Television receivers use cathode ray tubes except in special cases, but recently the high voltage applied to brighten the image has reached over 30KV, and the beam current applied has also increased to over 2A. X-ray radiation from cathode ray tubes has become a problem. Therefore, it is natural that no X-rays are emitted under normal usage conditions, but in countries such as the United States and Canada, even in the event of an accident with a television receiver, the amount of X-rays emitted must be kept below a certain level. It is now common practice for television receivers to be equipped with X-ray protection devices. Since the amount of X-ray radiation is a function of the product of the voltage applied to the cathode ray tube and the flowing beam current, it is ideal for this X-ray protection device to operate by detecting both high voltage and beam current.

A conventional X-ray protection device is shown in FIG.

In FIG. 1, the output of a horizontal oscillation circuit 1 which is operated by being supplied with DC power +B2 via a resistor R is connected to the primary winding T of a flyback transformer T via a horizontal drive circuit 2 and a horizontal output circuit 3. The high voltage obtained from the high voltage winding T2 is applied to the cathode ray tube (
(not shown). This X-ray protection device detects high voltage using the detection winding T3 of the flyback transformer T, and uses this detection output to conduct the P-gate thyristor 4 to stop the horizontal oscillation of the horizontal oscillation circuit 1. ing. To explain in more detail, the pulse obtained from the detection winding T3 of the flyback transformer T is rectified and smoothed by the diode D2 and the capacitor C, divided by the resistors 2 and R3, and then sent to the thyristor 4 via the Zener diode D3. It is added to gate 4a. On the other hand, the cathode 4b of the thyristor 4 is a diode D.
The anode 4c of the thyristor 4 is connected to the negative terminal of the high voltage winding T2 of the flyback transformer T through the resistor R4 and R5, and the anode 4c of the thyristor 4 is connected to the negative terminal of the high voltage winding T2 through the resistor R4 and R5. It is connected to the power input terminal la of the horizontal oscillation circuit 1. Note that R7 and R8 are each a resistor, C2 and C3 are each a capacitor,
D6 is a diode, and the anode side terminal of diode D6 is connected to a video circuit (not shown). Now, if the high voltage increases for some reason, the pulse voltage of the detection winding T3 also increases, and as a result, the detected DC voltage output from the connection point of the resistors R2 and R3 increases.

When this detected DC voltage becomes equal to or higher than the Zener voltage of the Zener diode D3, the Zener diode D3 becomes conductive and the sirensor diode D3 becomes conductive. Thyristor 4
becomes conductive, the power supply input terminal l of the horizontal oscillation circuit 1
a is grounded, and the horizontal oscillation of the horizontal oscillation circuit 1 is stopped.
As a result, high voltage is no longer generated from the high voltage winding T2 of the flyback transformer T. The high voltage value that stops this horizontal oscillation can be arbitrarily set by changing the division ratio of resistors R2 and R3. On the other hand, if the beam current increases, the voltage at the connection point between the resistors R5 and R8 becomes negative, and the current feedback biases the cathode 4b of the thyristor 4 negatively, causing the thyristor 4 to conduct at a lower voltage. The operation start voltage that stops horizontal oscillation becomes lower. However, such conventional X-ray protection devices have the following drawbacks. [a} FIGS. 2A, B, and C show the collector voltage waveform, collector current waveform, and base voltage waveform of the horizontal output transistor of the horizontal output circuit 3, respectively, and FIG. 2D shows the horizontal drive transistor of the horizontal drive circuit 2. As can be seen from these figures, the horizontal output circuit 3 of the television receiver is configured to be in the off state when the horizontal drive circuit 2 is in the on state. When the horizontal oscillation of the horizontal oscillation circuit 1 stops, the horizontal drive circuit 2 is turned off and the horizontal output circuit 3 is turned on.

Therefore, the moment the X-ray protection device operates, the horizontal output circuit 3 is always turned on. Now, in Figure 2,
When the x-ray protection device operates at time t, collector current flows through the horizontal output transistor even though a high pulse voltage is generated, so the collector loss of the horizontal output transistor increases rapidly between times t and t2. The horizontal output transistor is destroyed. [b- Due to the large number of parts,
There are large variations in the high voltage that stops horizontal oscillation, that is, the high voltage that starts operation.

In particular, P-gate thyristors generally have low sensitivity and a wide variation in sensitivity, so the variation due to the excessive number of components and the variation in the high voltage value that stops horizontal oscillation are extremely large. Furthermore, since there are many parts, there is also the problem of high cost. Therefore, an object of the present invention is to provide an X-ray protection device that can reduce variations in the high voltage value at the start of operation without destroying the horizontal output transistor.

An embodiment of this invention is shown in FIG.

In the figure, the output of a horizontal oscillation circuit 1, which is operated by being supplied with a DC power supply B2 through a series circuit of a resistor R and a Jenner diode D7, is transmitted through a horizontal drive circuit 2 and a horizontal output circuit 3 to a flyback transformer T. The high voltage obtained from the high voltage winding T2 is applied to the anode of the cathode ray tube via the diode D. This X-ray protection device detects high voltage using the detection winding T3 of the flyback transformer T, and uses this detection output to conduct the N-gate thyristor 5 to stop the horizontal oscillation of the horizontal oscillation circuit 1. ing. More specifically, the pulse as shown in FIG. 4A obtained from the detection winding T3 of the flyback transformer T passes through the capacitor C4 to remove the DC component, and the pulse as shown in FIG. 4B is passed through the diode D8 as shown in FIG. After the peak value is clamped to ground, it is applied to the gate 5a of the thyristor 5 via the resistor R9, and this gate 5a is connected to the resistor R, o.
are connected to the connection point of the resistor R and the turner diode D7, and the voltage of the DC power supply +B2 is applied to the resistors R, . It is connected to the negative side terminal of the high voltage winding T2 of the flyback transformer T via. The voltage waveform of the gate 5a of the syristor 5 is the sum of the voltage of the DC power supply +B2 and the pulse voltage of FIG. 4B, as shown by the solid line 1 in FIG. 4C. On the other hand, the anode 5b of the thyristor 5 is connected to the connection point between the horizontal oscillation circuit 1 and the Zener diode D7 via the resistor R,2, and is connected to the voltage of the DC power supply +& as shown by the solid line B in Fig. 4C. A voltage as low as the Zener voltage of the Zener diode D7 is applied, and the thyristor 6
The cathode 5c of is grounded. Note that C6 is a capacitor. Now, if the high voltage increases for some reason, the voltage of the pulse in the detection winding L will also increase, causing the thyristor 5 to rise.
gate voltage is pushed down.

When the gate voltage of the thyristor 5 becomes lower than the anode voltage (solid line b in FIG. 4C) as shown by the broken line m in FIG. 4C, the thyristor 5 becomes conductive. As a result, the power input terminal la of the horizontal oscillation circuit 1 is grounded, the horizontal oscillation of the horizontal oscillation circuit 1 is stopped, and high voltage is no longer generated from the high voltage winding L of the flyback transformer T. The high voltage value for stopping this horizontal oscillation can be arbitrarily set by selecting the resistors R9, R, and o. On the other hand, if the beam current increases, the voltage at the negative terminal of the high-voltage winding L of the flyback transformer T becomes negative, and current feedback causes the resistors R, . The gate voltage of the thyristor 5 is lowered through the lower high voltage, thereby making the thyristor 5 conductive at a lower high voltage, thereby lowering the operation start high voltage to stop horizontal oscillation. In this way, the X-ray protection device of this embodiment has the DC component removed from the pulse voltage of the detection winding T3 of the flyback transformer T at the gate 5a of the thyristor 5, and its peak is clamped to the ground level. The pulse voltage of the detection winding T3 increases by adding and adding the voltage of the DC power supply + B2 and applying a voltage lower than the voltage of the DC power supply + B2 by the Zener voltage of the Zener diode D7 to the anode 5b of the thyristor 5. In this case, the gate voltage of the thyristor 5 is lowered accordingly, and when the voltage drops below the anode voltage, the thyristor 5 is made conductive to stop horizontal oscillation. When the thyristor 5 becomes conductive, the high voltage and beam current can be detected to accurately prevent X-ray radiation, and the destruction of the horizontal output transistor as described in the conventional example can be prevented.

In addition, since there are fewer parts compared to the conventional example, there is less variation in the high voltage at which the operation starts, and the cost is lower. Furthermore, since the peak of the flyback pulse is used, it is possible to accurately respond to various accident modes in which high pressure increases and prevent X-ray radiation. As described above, the X-ray protection device of the present invention can accurately prevent X-ray radiation by detecting beam current at high voltages, protect horizontal output transistors from destruction, reduce the number of parts, and operate at high voltages. This has the effect of reducing the variation in

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a conventional X-ray protection device, Fig. 2 is a waveform diagram to explain its drawbacks, Fig. 3 is a circuit diagram of an embodiment of the present invention, and Fig. 4 explains its operation. FIG. 1...Horizontal oscillation circuit, 2...Horizontal drive circuit, 3...Horizontal output circuit, 6...Thyristor, R,,
R9, R, o, R river R, 2...Resistance, C4...
・・・Capacitor, D7・”...Zener diode,
D8・”…Diode, T…Flyback transformer,
T,...Primary winding, T2...High voltage winding, T3...
...Detection winding. Figure 1 Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1 horizontal oscillation circuit and a first
a DC power supply, a thyristor whose anode is connected to the power input terminal of the horizontal oscillation circuit and whose cathode is grounded, and a voltage higher than the voltage of the first DC power supply by a predetermined value is supplied to the gate of the thyristor. a second DC power source, a flyback transformer, a clamp circuit that clamps the flyback pulse obtained from the flyback transformer so that its peak is at the ground level and supplies it to the gate of the thyristor; An X-ray protection device comprising: a current feedback circuit that returns the current flowing through the thyristor to the gate of the thyristor to lower the gate voltage.