JPH02248185A - Degaussing circuit - Google Patents

Abstract

PURPOSE:To obtain an inexpensive circuit able to following to the consecutive operation by generating a pulse whose pulse width is reduced timewise at a prescribed frequency so as to control a switch element such as a triac and an electromagnetic relay or the like. CONSTITUTION:When a switch 2 is closed, a pulse whose pulse width is decreased gradually with time is outputted from a pulse generating circuit 14 and a triac 5 is turned on/off corresponding to the high/low level of the pulse and the on-period is reduced gradually as time. Thus, a degaussing current whose flowing period is reduced gradually as time flows to the degaussing coil 4. Since no component having a thermal capacity such as positive characteristic thermister is in use, the circuit able to operate degaussing continuously is inexpensively obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a degaussing circuit for preventing color shift and two-color unevenness on the screen due to the influence of earth's magnetic field in a color display monitor using a cathode ray tube.

2. Description of the Related Art In recent years, color display monitors using cathode ray tubes have been used as terminals such as personal computers and computer graphics devices such as 2.\\-/ and CAD/CAM. One of the indispensable functions of such color display monitors is a degaussing function that can prevent color shift and two-color unevenness on the screen due to the influence of earth's magnetic field.

Below, Fig. 6 shows the conventional general demagnetizing force formula.

This will be briefly explained based on FIG. In the current cathode ray tube for color display, a shadow mask is provided in front of the phosphor as a guide means so that each of the red, green, and blue beams hits a predetermined phosphor. However, when this shadow mask is magnetized by earth's magnetism, the traveling direction of the beam current changes from the normal state, and the beam current no longer hits the predetermined phosphor. As a result, 9 color irregularities occur, but the degaussing circuit causes color shift.

In order to remove the magnetization component of the shadow mask that causes color unevenness, an alternating current whose peak value gradually decreases over time as shown in FIG. 6 is passed through the degaussing coil. The degaussing coil placed around the shadow mask, that is, around the cathode ray tube, generates degaussing magnetic flux corresponding to the alternating current whose peak value gradually decreases over time as described above, so the shadow mask is gradually degaussed. To go. Here, in order to obtain an alternating current whose peak value gradually decreases over time, the seventh
A positive temperature characteristic thermistor having positive temperature characteristics as shown in the figure is used. A positive characteristic thermistor self-heats due to electric current.
Since the resistance value increases with temperature, the current value has a characteristic of gradually decreasing in inverse proportion.

Next, a conventional degaussing circuit will be explained with reference to FIG. FIG. 5 is a circuit diagram showing an example of a conventional degaussing circuit. In Fig. 5, 1 is an AC power supply, 2 is a switch, 3 is a positive temperature coefficient thermistor, 4 is a degaussing coil, 5 is a triac, 6 and 9 are resistors, 7 is a capacitor for noise prevention, and 8 is a phototriac as a light control element. , 1o is a pulse generation circuit. A positive characteristic thermistor 3 and a demagnetizing coil 4 are used to cause the demagnetizing current shown in FIG. 6 described above to flow through the demagnetizing coil.
are connected in series to one end of the AC power supply 1 via the switch 2,
Furthermore, in order to perform 0N10FF control of the demagnetizing current, a triac 5 is added as a switching element between the demagnetizing coil (V4) and the other end of the AC power supply.

Now, when switch 2 is turned on, pulse generation circuit 1Q
When the pulse generated by the photodiode reaches a high level, a current flows to the photodiode side of the phototriac 8, and the phototriac is turned on by optical control. Then, an alternating current flows through the phototriac 8 as a gate trigger current for the triac 5, turning on the triac 5.
state. As a result, an alternating current, that is, a demagnetizing current whose peak value gradually decreases with time flows through the positive characteristic thermistor 3 to the demagnetizing coil I/4 as described above.

After the shadow mask is sufficiently demagnetized, the pulse from the pulse generating circuit 10 becomes low level and turns the rephoto triac 8 into an FF state, so that the gate current of the triac 5 is also adjusted to the correct size, and the triac 5 becomes an FF state. At this point, no current flows completely through the demagnetized coil/L/4.

Problems to be Solved by the Invention However, in the conventional degaussing circuit, a positive temperature coefficient thermistor is indispensable in order to obtain an alternating current that gradually decreases over time. However, considering the positive characteristic 5 and the heat capacity of the thermistor, it cannot follow the continuous operation of the degaussing function. In other words, in the second and subsequent degaussing operations, the positive temperature coefficient thermistor has not been sufficiently cooled, and therefore the resistance value has not returned, so the resistance value is greater than when it was cooled, and the degaussing current decreases, so that the degaussing function cannot be fully performed. There will be no such thing.

In view of the above problems, it is an object of the present invention to provide a relatively inexpensive degaussing circuit that can sufficiently follow continuous operation without using a positive temperature coefficient thermistor.

Means for Solving the Problem In order to achieve this object, the degaussing circuit of the present invention includes a primary circuit in which a degaussing coil and a switching element such as a triac or an electromagnetic relay are connected in series at both ends of an AC input power source, and - Turn on/off switch elements such as liacs and electromagnetic relays.
The configuration includes a secondary circuit that generates a pulse whose control frequency is constant and whose pulse width gradually decreases over time to turn off the power.

Effect 6 ＼ This configuration provides a relatively inexpensive demagnetizing circuit that can sufficiently perform the demagnetizing function even in continuous operation by not using a positive temperature coefficient thermistor.

Embodiment Hereinafter, an embodiment of the degaussing circuit of the present invention will be described with reference to the drawings.

1 and 2 are circuit diagrams showing the configuration of a degaussing circuit in an embodiment of the present invention.
is an electromagnetic relay, 12 is a resistor, 13 is a transistor, 14
is a pulse generating circuit (a pulse generating circuit whose frequency is constant and whose pulse width gradually decreases); the other components are the same as the conventional configuration shown in FIG.

First, regarding the operation of the degaussing circuit configured as described above.
Let me explain with a diagram.

Now, when the switch 2 is turned on, the pulse generation circuit 14 on the secondary side generates a pulse whose pulse width gradually decreases over time (
However, the frequency is constant), and the triac 5 is in the ON state 10 in response to the high level and low level of the pulse.
It is in the FF state, and the ON period gradually decreases over time.

On the other hand, the triac 5 operates only when the AC voltage drops to o [V:]. By using a so-called zero cross function, the demagnetizing current flowing through the demagnetizing coil/I/4 starts flowing from 0 [C] as shown in FIG. 4, and the period during which the demagnetizing current flows gradually decreases with time. That is, the degaussing operation becomes weaker with time and ends when the pulse width generated by the pulse generating circuit 14 becomes O.

Since this circuit does not use components with heat capacity such as a positive temperature coefficient thermistor, the above operation can be repeated sufficiently even in the case of continuous demagnetization operation, so that the circuit can sufficiently perform its function.

Next, in FIG. 2, an electromagnetic relay 11 functions as a switching element instead of the triac 5, but the basic operation is the same as that in FIG. 1, so a description thereof will be omitted.

FIG. 3 shows an embodiment of the pulse generating circuit 14 in which the frequency is constant and the pulse width gradually decreases with time.

In FIG. 3, 15 is a sawtooth wave generating circuit, 16 is a resistor, 17 is a large-capacity electrolytic capacitor, and 18 is an operational amplifier.

Now, a sawtooth wave with a constant frequency is applied to the (+) terminal of the operational amplifier 18, and on the other hand, the voltage charged to the large-capacity electrolytic capacitor 17 via the resistor 16 to the (-) terminal as a comparison voltage increases with time. Since the period during which the sawtooth voltage is greater than the comparison voltage decreases with time, operational amplifier 1
At the output terminal 8, a desired pulse whose pulse width gradually decreases over time and whose frequency is constant is obtained.

As described above, the degaussing circuit of the present invention can provide a relatively inexpensive degaussing circuit that can sufficiently follow multiple continuous operations without using a positive temperature coefficient thermistor.

[Brief explanation of drawings]

FIGS. 1 and 2 show the first embodiment of the present invention. A circuit diagram of a degaussing circuit in the second embodiment, FIG. 3 is a circuit diagram showing an example of a pulse generating circuit whose frequency is constant and the pulse width gradually decreases with time, and FIG. 4 is a circuit diagram of a degaussing current in the degaussing circuit of the present invention. FIG. 5 is a circuit diagram of a conventional degaussing circuit, FIG. 6 is a waveform diagram of a degaussing current in a conventional degaussing circuit, and FIG. 7 is a characteristic diagram of a positive characteristic thermistor. 1... AC power supply, 2... Switch, 4
... Demagnetizing coil, 5 ... Triac, 8
...Photo 1-Liac, 10...Pulse generation circuit 1.11...Electromagnetic relay, 14...
... Pulse generation circuit 2.15 ... Sawtooth wave generation circuit, 17 ... Large capacity electrolytic capacitor, 18
...Op amp. Name of agent Patent attorney Shigetaka Awano and 1 other person Ku ('U) Tang W Banashi Tozuka

Claims (1)

[Claims] A primary circuit in which a degaussing coil and a switching element such as a triac or an electromagnetic relay are connected in series at both ends of an AC power supply, and a constant frequency circuit for controlling on/off of the switching element such as the triac or electromagnetic relay. A degaussing circuit comprising: a secondary circuit that generates a pulse whose pulse width gradually decreases over time.