JPS6138673B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a demagnetizing circuit for demagnetizing a cathode ray tube or the like of a television receiver.

FIG. 1 is a circuit diagram showing a conventional degaussing circuit.
In the figure, 1 is an AC power supply, 2 is a temperature-sensitive resistance element (hereinafter referred to as a positive temperature coefficient thermistor) which is sensitive to element temperature and whose resistance value increases as the temperature rises, and 3 is a degaussing coil.

FIG. 2 shows the waveform of the current flowing through the circuit of FIG. Immediately after the AC voltage is applied, the element temperature of the PTC thermistor 2 is low and its resistance value is small, so a large current flows, but as this current flows, the temperature of the PTC thermistor 2 rises, and its resistance value gradually increases. Therefore, the current decreases over time.

If the degaussing coil 3 is installed near the cathode ray tube, the cathode ray tube magnetized by earth's magnetism or the like can be demagnetized using the magnetic field generated by the current flowing through the degaussing coil. At this time, the current flowing through the demagnetizing coil 3 is gradually reduced by the positive temperature coefficient thermistor 2, thereby preventing the cathode ray tube from being re-magnetized by the magnetic field generated in the demagnetizing coil 3.

However, the resistance value of the positive temperature coefficient thermistor 2 is
Since it is impossible to increase to infinity,
The current flowing through the degaussing coil 3 remains and does not become completely zero.

A drawback of the conventional degaussing coil is that, due to the influence of the magnetic field generated in the degaussing coil 3 by the residual current, the brightness flickers on the screen of the cathode ray tube, making it difficult to see the screen.

SUMMARY OF THE INVENTION An object of the present invention is to provide a degaussing circuit that eliminates the drawbacks of the prior art described above and does not cause brightness flickering on the screen of a cathode ray tube.

The present invention is characterized in that after the current flowing through the degaussing coil is gradually reduced by a positive temperature coefficient thermistor, the two-way conducting element with a control pole is made non-conductive, and the current flowing through the degaussing coil is gradually cut off.

Hereinafter, the present invention will be specifically explained with reference to Examples.

FIG. 3 is a diagram explaining the principle of the present invention.
In the figure, 4 is a switch.

FIG. 4 shows the waveform of the current flowing through the degaussing coil 3 in the circuit shown in FIG. First, when the switch 4 is short-circuited and an alternating current voltage is applied, a current similar to that shown in FIG. 2 flows. When the switch 4 is opened when this current has decreased to a certain extent, the current flowing through the degaussing coil 3 is briefly cut off. After the current is interrupted, no magnetic field is generated in the degaussing coil 3, and therefore the brightness of the cathode ray tube screen does not flicker, which was a drawback of the conventional method.

FIG. 5 shows an example of a specific circuit. An AC power source 1 is connected to a circuit in which a degaussing coil 3 and a two-way conduction element 5 with a control pole are connected in series, a resistor 6 is connected in parallel with this series circuit, and a positive temperature coefficient thermistor 2 is connected in series with the parallel circuit. Apply an AC voltage of One terminal 7 of the two-way conduction element 5 with a control pole and the control pole 9 are connected through a resistor 10 as a gate circuit. An alternating current voltage is applied between one terminal 7 and the other terminal 8 of the two-way conducting element 5 with a control pole via the positive temperature coefficient thermistor 2 and the degaussing coil 3. When the voltage at one terminal 7 is higher than the voltage at the other terminal 8, a voltage higher than that at the terminal 8 is applied to the control pole 9 through the resistor 10, so that the two-way conduction element 5 with a control pole becomes conductive. Further, when the voltage at one terminal 7 is lower than the voltage at the other terminal 8, a voltage lower than that at the terminal 8 is applied to the control pole 9 through the resistor 10, so that the two-way conduction element 5 with a control pole Conduct. As described above, the two-way conduction element 5 with a control pole allows current to flow in both directions according to the alternating current voltage applied between the terminals 7 and 8.

By the way, in order to make the two-way conduction element with control pole 5 conductive, in addition to the gate voltage applied to the control pole 9 described above, a current flowing through the two-way conduction element with control pole 5 is generally called a holding current. It is necessary to have a current value higher than a certain current value.
Therefore, immediately after applying the AC voltage of AC power supply 1,
When the temperature of the positive temperature coefficient thermistor 2 is low and therefore its resistance value is small, the current flowing through the series circuit consisting of the degaussing coil 3 and the two-way conducting element with control pole 5 is large, so the two-way conducting element with control pole 5 is However, as the temperature of the PTC thermistor 2 increases due to the current flowing through the PTC thermistor 2, and its resistance value increases, the current flowing through the series circuit consisting of the degaussing coil 3 and the two-way conducting element with control pole 5 gradually decreases. When the resistance value of the positive temperature coefficient thermistor 2 decreases and further increases, the holding current cannot flow through the two-way conductive element 5 with a control pole, so the two-way conductive element 5 with a control pole becomes non-conductive.

If the resistance value of the resistor 6 is selected to be sufficiently smaller than the resistance value of the PTC thermistor 2 at high temperature, even after the two-way conduction element 5 with control pole becomes non-conductive, the current will flow to the PTC thermistor 2 through the resistor 6. As a result, the temperature of the PTC thermistor 2 is kept at a high temperature,
Its resistance value is also kept high. Therefore, the two-way conducting element 5 with control pole is also kept non-conducting.

Here, if the resistance value of the resistor 6 is selected to be sufficiently larger than the resistance value of the series circuit consisting of the degaussing coil 3 and the two-way conduction element with control pole 5 when the two-way conduction element with control pole is conductive, the degaussing coil In 3,
A current with a waveform similar to that shown in FIG. 4 flows.

When using a positive temperature coefficient thermistor, a degaussing coil, and a two-way conduction element with a control pole that are currently used in general degaussing circuits, it is easily possible to select the resistance value of the resistor 6 to satisfy the above conditions. It is.

According to the present invention, after effectively demagnetizing the cathode ray tube by gradually reducing the current flowing through the degaussing coil 3 using the positive characteristic thermistor 2, the two-way conducting element 5 with control pole is made non-conductive, and the current flowing through the degaussing coil 3 is made non-conductive. Since the flowing current is quickly interrupted, flickering in the brightness of the cathode ray tube screen, which conventionally occurs due to residual current flowing through the degaussing coil 3, does not occur.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a conventional degaussing circuit, Figure 2 is a diagram showing the current waveform flowing through the degaussing coil in Figure 1, Figure 3 is a circuit diagram for explaining the principle of the present invention, and Figure 4 is FIG. 3 is a diagram showing a current waveform flowing through the degaussing coil 3, and FIG. 5 is a specific circuit diagram showing an embodiment of the degaussing circuit according to the present invention. 1: AC power supply, 2: Positive characteristic thermistor, 3: Demagnetizing coil, 5: Two-way conduction element with control pole, 6: Resistor, 10: Resistor.

Claims (1)

[Claims] 1 A two-way conductive element with a control pole having a first and second terminal and a control pole, and a first resistor connected between the first terminal and the control pole of the two-way conductive element with a control pole. , a degaussing coil connected in series to a two-way conductive element with a control pole, and a series circuit consisting of a two-way conductive element with a control pole and the degaussing coil, a positive polarizer connected in series and generating a gradually decreasing current in the degaussing coil. A degaussing circuit comprising a characteristic thermistor and a second resistor connected in parallel to the series circuit.