JPS63258183A - Automatic demagnetizing circuit - Google Patents

Abstract

PURPOSE:To automatically demagnetize periodically by providing a means to take out a vertical flyback pulse generated from a vertical deflection coil, and a switching means to demagnetize corresponding to the said taken-out vertical flyback pulse. CONSTITUTION:The base voltage of a transistor Q2 gradually rises similarly to a pulse during every vertical flyback period, and when it becomes higher than the base voltage of a transistor Q1, the collector current flows in a transistor Q3, hence a current is supplied to the gate of a thyrister SCR through a resistor R6, and thus the thyrister is operated. At such a time, the changes accumulated in a capacitor C1 starts to discharge through a demagnetizing coil L1 and the thyrister SCR. At a point P1, the discharge of the capacitor C1 ends, and because of the action of the coil L1, the current continues to flow as reducing until reaching a point P2 where it comes to zero. After the completion of this demagnetizing operation, the base voltage of the transistor Q2 is made rise again by a vertical flyback pulse to turn on the thyrister SCR, and the demagnetizing operation is repeated.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a circuit for demagnetizing color televisions, CRT displays, and the like.

<Summary of the Invention> The present invention comprises a means for extracting a vertical retrace pulse generated from a vertical deflection coil, and a switching means for demagnetizing in accordance with the input of the vertical retrace pulse extracted by the means. Demagnetization is automatically performed every period.

<Conventional technology> When changing the position and direction of color TV and CRT displays during image reception, it is necessary to demagnetize the plow/tube, etc. to eliminate the influence of earth's magnetic field.

Conventionally, degaussing was performed manually by switching a switch by operating a push button each time the position and direction of the image receptor changed.

An example of this conventional circuit is shown in Figure 6. In Fig. 6, terminal a of push button switch 1 is connected to an appropriate C power source in the image receiver. Common terminal C contacts terminal a.

Capacitor 2 connected between terminal C and ground is kept charged in the polar direction shown in Figure 6. When the push button is pressed, common terminal C of switch 1 is disconnected from terminal a and comes into contact with terminal B. A degaussing coil 3 is connected between terminal B and the ground (#), and at this time, damped vibration occurs between the capacitor and the coil, and a current as shown in Figure 7 flows through the degaussing coil 3, resulting in a damped alternating current. The magnetic field demagnetizes the image receptor.

When the degaussing operation is completed and you release the push button, switch 1 is activated.

It returns to normal use and waits for the next degaussing operation.

<Problems to be Solved by the Invention> However, the conventional technology has the following problems.

1) It is necessary to manually degauss each time the position and direction of the display receiver changes. Especially for CRT displays mounted on moving objects such as marine equipment, the frequency of degaussing does not increase. It's rare.

2) Screen display is disrupted during the degaussing operation.

SUMMARY OF THE INVENTION In order to eliminate the above-mentioned drawbacks, it is an object of the present invention to provide a circuit that automatically performs demagnetization during the retrace period of vertical scanning of a television receiver.

Means for Solving the Problems> The present invention comprises means for extracting a vertical retrace pulse from a vertical deflection coil, and switching means for demagnetizing in response to input of the vertical retrace pulse extracted by the means.

Effect> As described above, the vertical deflection coil is automatically demagnetized by the vertical retrace pulse.

<Example> Embodiments of the present invention will be described in detail below using one drawing.

Figure 1 shows an example of the present invention. In the figure, when demagnetization is not being performed, capacitor C1 is charged in the polarity direction indicated on capacitor 01 through the charging circuit and resistor R8.

The vertical retrace pulse generated at one end of the vertical deflection coil LVY passes through a differentiating circuit of capacitor 08 and resistor R9,
Furthermore, the negative direction component is cut by diode D3, and the voltage waveform at point 0 in Figure 1 becomes as shown in Figure 2 (a).

This voltage further passes through resistor RIO and R5 and charges capacitor C2.

Since the resistors R10 and R5 and the capacitor C2 form an integrating circuit, the voltage waveform at point ■ in Figure 1 is a vertical retrace line from the start point to the start of demagnetization as shown in Figure 2 (b). It increases gradually every period.

Transistors Ql and Q2 form a differential amplifier, and during a period when the base voltage of transistor Q2 is lower than the pace voltage of transistor Q1 (the voltage given by the resistance division of resistor R1 and resistor R2), the collector of transistor Q2 No current flows. The base voltage level of this transistor Q1 is clearly shown in Figure 2 (c) with a chain double-dashed line.

The pace voltage of transistor Q2 (point ■ in Figure 1) is obtained by superimposing the waveform obtained by dividing the voltage waveform in Figure 2 (a) by resistance RIO and resistor R5 on the voltage waveform in Figure 2 (b). The waveform is shown in Figure 2 (c).

In the figure, the pace voltage of transistor Q2 gradually increases in a pulse-like manner every vertical retrace period, and when it rises higher than the pace voltage of transistor Q1, the collector current of transistor Q2 flows and the pace voltage of transistor Q3 decreases, and the pace voltage of transistor Q3 decreases. Since the collector current of Q3 flows, the resistance R
Current is supplied to the gate of thyristor SCR through 6, and thyristor SCR becomes conductive.

At this time, the charge charged in capacitor C1 passes through degaussing coil L1 and thyristor SCR and starts discharging. Figure 3(d) shows the waveform of the current flowing through the degaussing coil L.
Figure 3 (e) shows the charging voltage waveform of capacitor C1, and Figure 3 (f) shows the voltage waveform at point ■ in Figure 1.

] The discharge of capacitor 01 ends at point 21 in the barrel diagram, but due to the action of degaussing coil L, the current flows while decreasing until point P2, and becomes zero at point P2. Direction opposite to the polarity shown in Figure 1 (negative direction)
will be charged to. The voltage at point ■ in Figure 1 is around 21 points, and the voltage at point ■ in Figure 2 also becomes higher, capacitor C2 starts discharging, and the voltage at point ■ in Figure 2 becomes negative, so capacitor C2 is charged in the opposite direction (the ground side is positive) and suddenly becomes a negative value, but after this, the diode D2. As this negative voltage is discharged through resistor R5, it gradually becomes the ground level.

Along with this, the pace voltage of transistor Q2 drops and becomes lower than the base voltage of transistor Q1, and the collector current of transistor Q2 becomes "off", so the base voltage of transistor Q3 increases and transistor Q3 becomes "off". , the gate current of thyristor SCR is stopped and thyristor SCR is cut off at 22 points. 22
At the point, the negative charge of the capacitor CI (the polarity shown in Figure 1 is positive) is discharged through the degaussing coil L1 of the capacitor C4, and current flows through the degaussing coil L in the opposite direction to the previous one. As mentioned above, the gate of the thyristor SCH is no longer supplied with current at this point, so it will not turn on until the next degaussing operation starts. Therefore, after the 22nd point, the damped vibration is repeated mainly by the series resonant circuit of the degaussing coil L and the capacitors 01 and C4, and the vibration ends at the P3 point.

In addition, since the capacitor C4 has a smaller capacitance value than C1, the period of vibration after the 22nd point is short, and the vibration is repeated many times within the limited time of the vertical retrace period. It can be repeated.

The period from the start of degaussing operation to the end of degaussing (point P3) is mainly determined by the winding resistance and inductance of degaussing coil L1, the capacitance values of capacitors c and C2, and the voltage value of the charging circuit, etc., and is determined at the time of design. Set an appropriate value so that the degaussing operation ends within the vertical retrace period.

After this degaussing operation is completed, the transistor Q2 is turned on again as described above.
The base voltage of R1 increases due to the vertical retrace pulse, and the thyristor SCR starts ONL and demagnetization operations, and this cycle period is mainly due to the resistance R1.
, R2, RIO, R5 resistance values and capacitor C2
It is determined by the capacitance value of , and can be set to an appropriate value depending on the purpose of the image receiver.

Also, in the pace voltage waveform of transistor Q2.

The top of the pulse section should be completely horizontal or sloped slightly downward to the right.

Otherwise, the start of degaussing will be triggered in the middle of the vertical retrace period, and the degaussing operation will not end within the vertical retrace period. This slope can be adjusted by changing the time constant of the differentiator circuit, which mainly consists of capacitor C3 and resistor R9.

Also, after the degaussing operation is completed, the capacitor C1 is charged through the resistor R8, but it is necessary to complete the charging operation after the next degaussing operation is completed, and this speed is determined by the resistor R8.
It can be set to an appropriate value by selecting the resistance value.

Note that diode D2 is a protection diode that prevents the base voltage of transistor Q2 from dropping excessively.

Other embodiments of the present invention are clearly shown in FIGS. 4 and 5.

Figure 4 shows the following changes from Figure 1.

1) The circuit of transistor Q1 has been abolished.

In this circuit, the necessary condition for the collector current of transistor Q2 to flow is that the base voltage of transistor Q2 is higher than the voltage given by the resistance division of resistors R1 and R4. Other conditions required for circuit operation are the same as those for the differential amplifier using combination K with transistor Q1 in Figure 6.

2) Switching thyristor SCR to bidirectional thyristor (TRIAC) T. In this case triac T
It is necessary to continue supplying current to the gate from the start of the degaussing operation until the end of the degaussing operation.

Capacitor 05 charges the electric charge necessary to continue supplying this current during the conduction period of transistor Q3,
After transistor Q3 is turned off, this charged charge is supplied to the gate of the triac through resistor R11 to prevent the triac from being cut off during the demagnetization period.

The second resistor R12 is provided for adjusting the triac gate voltage.

Also, capacitor c4 in Figure 1 is not needed when using the trybook, so it has been deleted.

In this case, during the degaussing period, the degaussing coil L.

Since the vibration is damped by the series resonant circuit of the capacitor C1 and the capacitor C1, the vibration period does not change at 22 points as in the example in Figure 3.

Figure 5 shows the triac T in Figure 4 and the thyristor SC.
The circuit is switched to a parallel connection circuit of R and diode D3, and the other parts are exactly the same as in Figure 4, and the circuit operation is also the same as in Figure 4.
It is no different from the figure.

Previously, degaussing was performed manually to eliminate the influence of geomagnetic field on the display image quality due to changes in position and direction, especially in color TV and color CRT displays mounted on moving objects such as ships and cars. . However, when the technology of the present invention is used, degaussing is performed automatically and periodically during the retrace period of vertical scanning, resulting in the following effects.

1) Frees you from the hassle of manually degaussing every time the display position changes.

2) The display screen is not disturbed during the degaussing operation.

3) If the degaussing operation requires a large amount of power consumption.

If the degaussing operation is performed every vertical retrace period, the power consumption of the display set will increase, but in the case of the circuit of the present invention, the degaussing operation is performed every fixed period during the vertical retrace period. Therefore, power consumption can be reduced.

<Effects of the Invention> As described above, according to the present invention, it is possible to provide a useful automatic demagnetization circuit that can automatically and periodically demagnetize a vertical deflection coil.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing one embodiment of the present invention, Figures 2 and 3 are circuit diagrams showing one embodiment of the present invention.
The figures are a waveform diagram of Fig. 1, Figs. 4 and 5 are circuit diagrams showing other embodiments of the present invention, Fig. 6 is a circuit diagram showing a conventional example, and Fig. 7 is a circuit diagram showing another embodiment of the present invention.
The figure is a waveform diagram of FIG. 6. LVY...Vertical deflection coil, Ll...Degaussing coil. Agent Patent attorney Takeshi Sugiyama (1 other person) 4 Δ

Claims (1)

[Claims] 1. An automatic degaussing circuit comprising means for extracting a vertical retrace pulse generated from a vertical deflection coil, and switching means for demagnetizing in response to input of the vertical retrace pulse extracted by the means.