JPH062875U - Degausser - Google Patents

Abstract

(57) [Abstract] [Purpose] To make the demagnetizing ability constant for a CRT display device equipped with an auto universal switching power supply regardless of the high voltage system or low voltage system of the AC power supply. [Structure] The degaussing coil 6, the first thermistor 11 and the first switching element 12 are connected to the power supply lines 10a and 10b.
Connect in series between them. Further, the second thermistor 13 and the second switching element 14 are connected in parallel with the thermistor 11. The input voltage detection circuit 15 turns on the switching element 14 when detecting that the AC power supply is a 100V system. On the other hand, the timer circuit 16 outputs a pulse having a constant time width to the switching element 12 after the AC power is turned on.
By doing so, the same degaussing current flows through the degaussing coil 6 even if the AC power supply is a 100V or 200V system.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a degaussing device for a color television receiver or a color display monitor.

[0002]

[Prior art]

 Color cathode ray tubes (hereinafter referred to as CRTs) are used in color television receivers, color display monitors and the like. In this case, the shadow mask of the CRT is magnetized by an external factor such as geomagnetism, which causes color shift due to landing shift of the electron beam. Therefore, the display device is provided with a degaussing device for degaussing the shadow mask of the magnetized CRT for the purpose of preventing color shift.

In recent years, these CRT display devices have been required to have high definition and high color reproducibility in addition to the increase in size. Especially for color display monitors, an auto-universal switching power supply that does not require switching of the power supply voltage may be used because it has worldwide specifications. However, these degaussing devices do not have automatic voltage switching, and the same degaussing device is used in, for example, 100 V and 200 V display devices.

An example of a conventional degaussing device will be described with reference to FIG. In this figure, a power outlet, a power switch 2, and a rectifier circuit 3 are provided as a power source for a CRT, and a degaussing device 4 is provided on the power line. The degaussing device 4 comprises a thermistor 5 having a positive characteristic and a degaussing coil 6 connected in series between power supply lines.

In the degaussing device 4 thus configured, when the power switch 2 is turned on to operate the display device, an AC voltage is applied to the rectifier circuit 3. At this time, the rectifying circuit 3 rectifies the AC voltage and outputs a DC voltage. Then, an AC voltage is applied to the thermistor 5 and the degaussing coil 6, and a degaussing current flows through the degaussing coil 6. At this time, the thermistor 5 generates Joule heat, and its resistance value increases due to the temperature rise of the element itself. Therefore, the demagnetizing coil 6 is demagnetized by passing the attenuated AC current for a certain period of time.

[0006]

[Problems to be solved by the device]

 However, in a CRT display device having an auto-universal switch power supply that shares 100V and 200V AC power supplies, the current flowing through the degaussing coil 6 changes depending on the voltage of the AC power supply. For example, if the resistance values of the degaussing coil 6 and the thermistor 5 are set so as to obtain the optimum degaussing ability in the 100V system, the 200V system will be overkill. Further, if the resistance values of the degaussing coil 6 and the thermistor 5 are set so as to obtain the optimum degaussing ability in the 200V system, the degaussing ability is insufficient in the 100V system. Since the number of turns of the degaussing coil 6 cannot be easily changed, the resistance value of the thermistor 5 was set to be optimum at the midpoint between the 100V system and the 200V system. Therefore, there is a drawback that the optimum degaussing state cannot be obtained with either power supply voltage.

The present invention has been made in view of such conventional problems, and provides a degaussing device capable of automatically switching degaussing currents to different AC power supplies and flowing a constant degaussing current. The purpose is to provide.

[0008]

[Means for Solving the Problems]

 The present invention is a degaussing device for degaussing a display device of a CRT by passing a degaussing current through a series circuit of a degaussing coil connected to an AC power source and a thermistor having a positive characteristic, and a degaussing coil connected between lines of an AC power source. , The series connection of the first thermistor and the first switching element, the series connection of the second thermistor and the second switching element connected in parallel with the first thermistor, and the voltage of the AC power supply If the voltage is a low voltage system, the input voltage detection circuit that turns on the second switching element and a pulse with a predetermined width after the AC power is input or by a switch signal are output to turn on the first switching element. And a timer circuit according to the present invention.

[0009]

[Action]

 According to the present invention having such a feature, the input voltage detection circuit outputs an ON signal to the second switching element if the AC power source to which the display device is connected is a low voltage system. Further, the timer circuit outputs an ON signal having a constant time width to the first switching element. Then, a degaussing current of a specified amount flows through the degaussing coil via the first and second thermistors. After a certain period of time, the pulse signal from the timer circuit turns off and the degaussing current stops. On the other hand, when the display device is connected to the high-voltage power supply, the second switching element is turned off, and the degaussing current flows only through the first switching element. In this way, the type of power supply voltage is detected and an optimum degaussing current is made to flow through the CRT of the display device.

[0010]

【Example】

 A degaussing device according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a circuit diagram showing the configuration of the degaussing device of this embodiment. In this figure, a power supply socket 1, a power switch 2, a rectifier circuit 3, and a degaussing coil 6 are provided, as in the conventional example. In the present embodiment, the first thermistor 11, the first switching element 12, and the degaussing coil 6 are connected in series between the AC power supply lines 10a and 10b. The second thermistor 13 and the second switching element 14 are connected in series between the common connection terminal of the thermistor 11 and the switching element 12 and the power supply line 10a. Each of the first and second thermistors 11 and 13 has a positive temperature characteristic. The switching elements 12 and 14 are switches having bidirectional conduction characteristics controlled by an external signal applied to their control terminals, and are composed of, for example, triacs.

On the other hand, an input voltage detection circuit 15 is provided between the power supply lines 10a and 10b. The input voltage detection circuit 15 discriminates whether the voltage of the AC power supply applied between the power supply lines 10a and 10b is a low voltage system with a rated voltage of 100V, 110V or the like or a high voltage system with a rated voltage of 220V. In the case of a low voltage system, an ON signal is output to the control terminal of the switching element 14. It is assumed that the supply voltage fluctuates up to 90 to 130 V even in the 100 V system, and the supply voltage fluctuates up to 180 to 260 V even in the 200 V system.

A timer circuit 16 is provided at the control terminal of the switching element 12. The timer circuit 16 delays a predetermined time from the rise of the DC voltage output from the rectifier circuit 3 and outputs a pulse having a constant width. Further, the timer circuit 16 is provided with a trigger switch 17, and when the trigger switch 17 is turned on, a pulse having a constant width is similarly output.

Next, the operation of the degaussing device of the present embodiment having such a configuration will be described with reference to the signal waveform diagram of FIG. First, the display device is connected to a low-voltage power supply of 100 V system, and when the power switch 2 is turned on at time t _{0 as} shown in FIG. 2A, the rectifier circuit 3 rises at time T 1 and outputs a specified DC voltage. . The input voltage detection circuit 15 detects that the power supply voltage is 100V. In this case, the input voltage detection circuit 15 outputs an ON signal to the switching element 14 to make this element conductive. On the other hand, the timer circuit 16 receives a DC power supply from the rectifier circuit 3 and outputs a pulse at time t ₁ delayed from the time t ₀ by a certain time as shown in FIG. 2C. The time t ₁ is set so that the timer circuit 16 or the like does not malfunction due to noise generated when the power switch 2 is turned on. This pulse is given to the control terminal of the switching element 12 to make this element conductive.

Since the switching elements 12 and 14 are both in the conductive state from the time t _1, the AC power source flows to the degaussing coil 6 via the thermistors 11 and 13. If the initial resistance values of the thermistors 11 and 13 are set equal to each other, the degaussing current flowing through the degaussing coil 6 is twice as large as that of the thermistor 11 alone.

Eventually, the temperatures of the thermistors 11 and 13 rise, and their resistance values increase. For this reason, the degaussing current of the degaussing coil 6 decreases with the attenuation characteristic as shown in FIG. When Ya has been time T2 has elapsed from the time t ₁ Te, the output of the timer circuit 16 is turned off. Therefore, the switching element 12 is turned off and the degaussing current is cut off.

Since the resistances of the thermistors 11 and 13 after conduction are high and the residual current after degaussing is at a minute level, many degaussers generally do not have such a timer circuit 16. However, if a slight residual current flows through the degaussing coil 6, a slight screen shake may occur on the screen of the CRT. In order to prevent this, the degaussing period T2 is regulated by the timer circuit 16.

Next, when the display device is connected to a 200 V AC power source and the power switch 2 is turned on, the input voltage detection circuit 15 detects that the voltage is a high voltage system. In this case, the input voltage detection circuit 15 does not output a signal and the switching element 14 is in the off state. On the other hand, the timer circuit 16 outputs a signal after a certain period of time to make the switching element 12 conductive. At this time, the degaussing current flows through the degaussing coil 6 only through the thermistor 11. The current AC power supply is a 200V system, but since the applied voltage is almost doubled, the same degaussing current as the 100V system flows through the degaussing coil 6. Next, when a certain time T2 has passed, the output of the timer circuit 16 is turned off and the switching element 12 is shut off.

If the installation direction of the display device is changed during operation, the color purity may change due to the influence of geomagnetism or the like. In this case, when a person operates the trigger switch 17, a pulse of a constant time T2 as shown in FIG. 2C is output to the timer circuit 16, and the ON signal is output to the switching element 12 again. Also in this case, a pulse having a constant width is applied to the switching element 12 from time t _3, and a degaussing current having a damping characteristic as shown on the right side of FIG. 2D flows in the degaussing coil 6.

[0019]

[Effect of device]

 As described above, according to the present invention, the input voltage comparison circuit discriminates whether the AC power supply is a high voltage system or a low voltage system, and outputs an ON signal to the second switching element according to the value. Therefore, in a CRT display device having an auto-universal switching power supply, the degaussing ability can be made the same in the high-voltage system and the low-voltage system of the AC power supply. In addition, the provision of the timer circuit eliminates the small shake of the screen due to the residual degaussing current generated during the operation of the display device of the CRT.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a degaussing device according to an embodiment of the present invention.

FIG. 2 is a signal waveform diagram showing the operation of the degaussing device of the present embodiment.

FIG. 3 is a block diagram showing a configuration example of a conventional degaussing device.

[Explanation of symbols]

 1 Power Outlet 2 Power Switch 3 Rectifier Circuit 6 Degaussing Coil 11 First Thermistor 12 First Switching Element 13 Second Thermistor 14 Second Switching Element 15 Input Voltage Detection Circuit 16 Timer Circuit 17 Trigger Switch

Claims (1)

[Scope of utility model registration request] 1. A degaussing device for degaussing a CRT display device by passing a degaussing current through a series circuit of a degaussing coil connected to an AC power supply and a thermistor having a positive characteristic, the degaussing device being connected between lines of an AC power supply. A series connection body of a degaussing coil, a first thermistor and a first switching element, a series connection body of a second thermistor and a second switching element connected in parallel with the first thermistor, and a voltage of an AC power supply. Is detected, and if the voltage is a low voltage system, an input voltage detection circuit that turns on the second switching element, and a pulse of a predetermined width is output after the AC power is input or by a switch signal, and the first switching is performed. A degaussing device, comprising: a timer circuit for turning on an element.