JPH0342783Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to a degaussing circuit used in connection with color picture tubes such as color television receivers and color displays. This invention relates to a degaussing circuit that is made smaller.

FIG. 1 is a circuit diagram of a conventional degaussing circuit of particular interest to this invention. Referring to FIG. 1, a first positive temperature coefficient thermistor 2 is connected in series to a degaussing coil 1. This serially connected degaussing coil 1
A shunt resistor 3 is connected in parallel to both ends of the first positive temperature coefficient thermistor 2 and the first positive temperature coefficient thermistor 2 . A second positive temperature coefficient thermistor 4 is connected in series to the degaussing coil 1, first positive coefficient thermistor 2, and shunt resistor 3 that are connected in parallel in this way. Then, the AC power supply 5 is connected via the switch 6 to one end of the degaussing coil 1, the first positive temperature coefficient thermistor 2, and the shunt resistor 3, which are connected in parallel, and one end of the second positive coefficient thermistor 4. given between the ends.

The first positive temperature coefficient thermistor 2 and the second positive coefficient thermistor 4 described above are ordinary positive coefficient thermistors having resistance-temperature characteristics as shown in FIG. In other words, the resistance of the positive temperature coefficient thermistor itself is
When the temperature exceeds a certain level, the temperature rises rapidly. The first positive temperature coefficient thermistor 2 and the second
The positive temperature coefficient thermistor 4 is thermally coupled to the positive temperature coefficient thermistor 4, as shown by the dotted line in FIG. The shunt resistor 3 is
A coil having a resistance value greater than the sum of the resistance value of the degaussing coil 1 and the resistance value of the first positive temperature coefficient thermistor 2 in the initial state is used. The switch 6 can be considered to be, for example, a power switch of a color television receiver or a switch linked to this power switch.

Next, the operation of the degaussing circuit shown in FIG. 1 will be explained. As an example, the resistance value of the first positive temperature coefficient thermistor 4 is 3Ω, the resistance value of the second positive coefficient thermistor 4 is 5Ω, the resistance value of the degaussing coil 1 is 8Ω, and the shunt resistor 3 is
Let the resistance value of be 100Ω. The first positive temperature coefficient thermistor 2 has a characteristic indicated by A in FIG.
The second positive temperature coefficient thermistor 4 has a characteristic indicated by B. Therefore, for a certain temperature increase, the first
This means that the resistance value of the positive temperature coefficient thermistor 2 increases faster than that of the second positive coefficient thermistor 4. When the switch 6 is closed, the resistance values of both the positive temperature coefficient thermistors 2 and 4 are small in the initial stage, and the resistance of the degaussing coil 1 and the first positive coefficient thermistor 2 is smaller than the resistance value of the shunt resistor 3. Since the value is smaller, a large current flows through the degaussing coil 1 along the route shown by the arrow 7. When a certain period of time elapses in this state, first the resistance of the first positive temperature coefficient thermistor 2 increases due to its Joule heat, and most of the current flows through the shunt resistor 3 along the route shown by the arrow 8, and the degaussing coil 1 Control the current flowing. Thereafter, after a certain period of time has elapsed in this state, the resistance of the second positive temperature coefficient thermistor 4 increases due to the heat generated by the module, and the circuit current is further controlled. At this time, since the first PTC thermistor 2 is thermally coupled to the second PTC thermistor 4, the temperature of the first PTC thermistor 2 further increases due to the heat of the second PTC thermistor 4. As a result, the resistance value of the first positive temperature coefficient thermistor 2 also becomes higher, and the current flowing through the degaussing coil 1 is further controlled, the degaussing current is made smaller, and the demagnetizing operation is completed. However, the current flowing through the degaussing coil 1 when such a degaussing operation is completed is several times
Although it is on the order of mA, it never becomes completely zero. Further, due to the characteristics of a positive temperature coefficient thermistor, the current flowing through the degaussing coil 1 oscillates as shown in FIG. 3, and also includes pulse noise. In order to remove such vibrations and pulse noise, a capacitor 9 is connected in parallel to the degaussing coil 1, as shown in FIG. 1, but it is impossible to completely remove them.

The degaussing current flowing through the degaussing coil 1 causes fluctuations in the electron beam in the color picture tube, which causes screen fluctuations and screen vibrations called dancing. This makes it impossible to obtain a stable image, and also makes it difficult to read characters on a color display or the like.

As a solution to this problem, the above-mentioned demagnetizing current may be further reduced, but the one shown in FIG. 1 has a limit. In addition to the above-mentioned capacitor 9, some measures have been taken, such as changing the way the degaussing coil is wound, but this is not perfect. Further, the switch 6 may be opened after the degaussing operation is completed, but this requires the addition of a complicated configuration.

Therefore, the main objective of this invention is to provide a degaussing circuit that can significantly reduce the degaussing current.

Simply put, this idea utilizes the so-called varistor effect of a positive temperature coefficient thermistor having a non-ohmic electrode in place of the first positive coefficient thermistor 2 shown in FIG. It is a combination of

Other objects and features of this invention will become clearer from the detailed description given below with reference to the drawings.

FIG. 4 is a circuit diagram of an embodiment of this invention.
4 differs from FIG. 1 in that a first positive temperature coefficient thermistor 10 is used in place of the positive coefficient thermistor 2 of FIG. 1, and that the capacitor 9 is removed. The other configurations are the same as those shown in FIG. 1, and corresponding parts are designated by the same reference numerals and redundant explanations will be omitted.

The first positive temperature coefficient thermistor 10 has a non-ohmic electrode such as silver, and the resistance-voltage characteristic of the non-ohmic electrode is shown in FIG. In other words, it has varistor-like characteristics, and when the voltage value becomes smaller than a certain value V0,
It changes greatly as the resistance value increases. When the voltage value is higher than the value V0, the resistance value is low and approximately constant.

Next, the operation of the degaussing circuit shown in FIG. 4 will be explained. First, the switch 6 is closed, but in this case, the voltage applied to the entire circuit is set in advance to a voltage higher than V0 (for example,
V1) is selected to be applied. Therefore, when the switch 6 is closed, the resistance value of the first positive temperature coefficient thermistor 10 is low (see FIG. 5), and most of the current flows through the degaussing coil 1 along the route shown by the arrow 7. After a certain period of time has elapsed in this state, the second positive temperature coefficient thermistor 4 begins to increase its resistance due to the Joule heat, and attempts to stabilize at a desired point. When the resistance value of the second positive temperature coefficient thermistor 4 increases, the voltage across it also increases proportionally, and most of the voltage applied to the entire circuit is applied to both ends of the second positive coefficient thermistor 4. become. As a result, as shown in FIG. 6, the voltage that was present across the first positive temperature coefficient thermistor 10 becomes smaller, and for example, V2 in FIG.
The value decreases to . At the same time, heat applied from the second PTC thermistor 4, whose temperature has already increased, to the first PTC thermistor 10 due to thermal coupling acts in the direction of further increasing the resistance value of the first PTC thermistor 10. Then, the resistance value of the first positive temperature coefficient thermistor 10 increases dramatically, and almost no current flows along the route shown by arrow 7, and the current flows along the route shown by arrow 8. . That is, in the circuit shown in FIG. 4, the current of the entire circuit is first controlled by the second positive temperature coefficient thermistor, and then the degaussing coil 1 is controlled by the varistor effect of the first positive coefficient thermistor 10. This is to better control the flowing current. In other words, the first positive temperature coefficient thermistor 10 exhibits ohmic properties when a high voltage is applied (above V0), but when a low voltage is applied (below V0),
For example, the fifth
The resistance value of R1 shown in the figure can be as high as several MΩ, and the demagnetizing current can be made negligible.

According to the embodiment shown in FIG. 4, the first positive temperature coefficient thermistor 10 only replaces the first positive coefficient thermistor 2 shown in FIG. Since the present invention can be realized in this embodiment, there is an advantage that the conventional mechanical structure can be used as is for this embodiment.

As described above, according to this invention, a positive temperature coefficient thermistor having a non-ohmic electrode is used, and since this is thermally coupled to a positive coefficient thermistor having an ohmic electrode, the properties of the non-ohmic electrode are Due to the synergistic effect of this and thermal coupling, the resistance value of the positive temperature coefficient thermistor portion having a non-ohmic electrode after the demagnetization operation is completed can be made much larger than that of the conventional one.
Therefore, after the degaussing operation is completed, more current can flow through the shunt resistor, and only a negligible amount of current flows through the degaussing coil. Since the current flowing through the degaussing coil is negligible, the screen of the color picture tube no longer shakes or dances.
A stable and clear image can be obtained. Also,
Since the two PTC thermistors are thermally coupled, they can be placed close to each other and a compact structure can be adopted. Further, it is not necessary to manage each positive temperature coefficient thermistor so that it conforms to the characteristics shown in FIG. 2, as in the conventional case, and the positive temperature coefficient thermistor according to this invention does not require so strict characteristic management. Furthermore, components such as the conventional capacitor 9 of FIG. 1 are no longer required.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional degaussing circuit of particular interest to this invention. FIG. 2 is a resistance-temperature characteristic diagram of the positive temperature coefficient thermistor shown in FIG. FIG. 3 is a waveform diagram of the current flowing through the coil when the degaussing operation is completed. FIG. 4 is a circuit diagram of an embodiment of this invention. FIG. 5 is a resistance-voltage characteristic diagram of a positive temperature coefficient thermistor having a non-ohmic electrode, which is a feature of this embodiment. FIG. 6 is a diagram showing changes in the voltage applied across the positive temperature coefficient thermistor having the non-ohmic electrodes. In the figure, 1 is a degaussing coil, 3 is a shunt resistor,
4 is a second positive temperature coefficient thermistor, and 10 is a first positive coefficient thermistor.

Claims (1)

[Claims for Utility Model Registration] A degaussing coil; a first positive temperature coefficient thermistor having a non-ohmic electrode connected in series to the degaussing coil; and the degaussing coil and first positive temperature coefficient thermistor connected in series. a shunt resistor connected in parallel to the degaussing coil and the first
a second positive temperature coefficient thermistor having an ohmic electrode connected in series with the positive coefficient thermistor and a shunt resistor and thermally coupled to the first positive coefficient thermistor.