KR19990003619U - Monitor degaussing circuit - Google Patents

Abstract

The present invention relates to a degaussing circuit for removing magnetized magnetism on a CRT in a monitor.

The circuit of the present invention generates a magnetic field when an alternating current flows, and is turned on by a degaussing coil L3 for demagnetizing the magnetic field magnetized on the CRT and a high level degaussing signal output from the microcomputer. In the degaussing circuit of the monitor comprising a transistor (Q21) to be applied to the degaussing coil, a diode (D21) for applying the degaussing coil after half-wave rectifying the alternating current, and And a degaussing capacitor C21 and a degaussing resistor R21 connected in parallel to the degaussing coil, respectively.

The present invention described above,

Description

Degaussing circuit of a monitor

The present invention relates to a degaussing circuit for removing magnetized magnetism on a CRT in a monitor, and in particular, a degaussing to remove spark noise generated in a degaussing coil when the monitor is in an off mode. Relates to a Singh circuit.

In general, a color display device focuses and accelerates hot electrons emitted from R, G, and B electron guns, collides with an RGB fluorescent surface through a point on a shadow mask to form pixels, and flows sawtooth currents through vertical and horizontal deflection coils. Form a 3D screen.

The color display device requires a very precise operation in order to form a high density pixel on a narrow screen. For this purpose, various correction devices, such as a purity magnet, a latent convergence magnet, a radial convergence magnet, and the like, are used. The degaussing coil is installed in the panel portion of the CRT to prevent deterioration of image quality due to geomagnetism and residual magnetism.

Here, the degaussing coil is a coil group wound around the panel of the CRT and connected to the power supply circuit of a monitor or a television, and an alternating current flows each time the power switch is turned on and off, and the alternating current flows as described above. It refers to a coil that element a shadow mask magnetized by geomagnetism or residual magnetism.

As is well known, the earth forms a geomagnetic field with one giant magnet, which affects a display element operated by an electric magnetic field such as a CRT. However, since the geomagnetic field is different depending on the position of the earth, it is difficult to uniformly correct it, and since the influence is not so large, the influence of the geomagnetic field is usually removed by the degaussing coil. have.

In other words, most televisions and monitors have a degaussing coil wound around the CRT, and if necessary, an alternating current flows through the degaussing coil to process magnetization by the geomagnetic field.

As shown in FIG. 1, a conventional circuit for processing degaussing may include a microcomputer 151, a relay driving transistor Q11, a relay RL1, a degaussing coil L3, and a transistor PR1. When the degaussing signal is input from the microcomputer 151, the contacts of the relay RL1 are connected to each other, and the alternating current is input through the line filters L1 and L2 and the X and Y capacitors C1, C2 and C3. Current flows through the degaussing coil L3 to remove the magnetized magnets in the CRT.

Prior to describing the conventional degaussing circuit, the driving of the power supply circuit connected to the degaussing circuit will be briefly described. The line filter L1 and the X capacitor C1 are commercial AC power inputted through a line. Noise and the like are removed from the AC, and the Y capacitors C2 and C3 bypass internal noise to ground to prevent noise, etc., generated when the diode bridge 100 is turned on and off from going out through the line. Let's do it.

As described above, the AC power in which the noise is removed is rectified by the diode bridge 100 and then flows through the primary winding of the transformer 120 through the inrush current preventing resistor R1 and the smoothing capacitor C4. At this time, the switching transistor Q1 is connected to the other side of the primary winding of the transformer and turned on or off in accordance with the output of the power control integrated circuit (eg, the 3842 PWM control IC) 110.

That is, the power control integrated circuit 110 receives a feedback signal Vfb through photo couplers 140a and 140b and receives a PWM signal of a predetermined frequency whose duty ratio is variable according to the magnitude of the feedback signal. The switching transistor Q1 is turned on or off in accordance with the PWM signal to flow or block a current input through the diode bridge 100 to ground.

For example, when the switching transistor Q1 is turned on, a + voltage is applied to the dot side of the primary winding of the transformer 120 so that a current flows through the switching transistor Q1, and the dot winding is turned in the + direction to the secondary winding. The voltage is induced and the voltage is applied to the diodes D2 and D3 in the reverse direction, thereby blocking the diodes D2 and D3 and accumulating energy in the primary winding.

Thereafter, when the switching transistor Q1 is turned off, the primary side of the transformer 120 suddenly stops flowing current, thereby inducing a voltage in a direction (dot side −) to continuously flow the current, and also on the secondary side. Voltage is induced so that the dot side becomes-, and forward voltage is applied to the diodes D2 and D3.

Therefore, on the secondary side, the output voltages Vout1 and Vout2 appear while charging the capacitors C6 and C7. Subsequently, when the switching transistor Q1 is turned on, as described above, the secondary diodes D2 and D3 are cut off, and the voltages of the capacitors C6 and C7 that have been charged are displayed on the output side.

As mentioned above, current flows in the primary winding during the period in which the switching transistor Q1 is turned on, and when the switching transistor Q1 is turned off, the energy is induced in the secondary winding by the first to second turns ratio. The induced voltage is represented as the secondary output DC voltages Vout1 and Vout2 through the rectifying diodes D2 and D3 and the smoothing capacitors C6 and C7. This method is called flyback converter and it is easy to configure the output voltage as multi because the secondary side configuration is simple.

Meanwhile, the operation of the conventional degaussing circuit connected to the power supply circuit of the monitor will be described below.

The microcomputer 151 outputs a signal for activating degaussing for degaussing when an appropriate condition such as power-on occurs. For example, when operating in an active 'high', the microcomputer 151 outputs a high level signal to the output port for degaussing.

When the microcomputer 151 outputs a high level signal, a bias is applied to the transistor Q11 in the forward direction through the resistors R11 and R12 and the capacitor C11, thereby turning on the transistor Q11. The relay RL1 is operated to apply an AC input AC power to the degaussing coil L3 through the transistor PR1 and the relay contact.

Here, the resistor PR1 is a thermosensitive resistor, and has a characteristic that the resistance increases gradually as the temperature increases. In the initial stage when an alternating current is input, since the resistance value of the transistor PR1 is small, a degaussing coil is used. A large amount of alternating current flows through L3, and as time passes, the temperature increases due to the alternating current, so that the resistance of the positive electrode PR1 increases gradually, so that the amount of current flowing through the degaussing coil L3 increases. It will gradually decrease.

That is, as shown in FIG. 2, the AC current of the attenuation vibration wave flows to the degaussing coil while the degaussing signal output from the microcomputer is at a high level. To decompose.

However, in the conventional degaussing circuit described above, if the microcomputer continuously outputs the degaussing signal of high level, the resistance value is higher than the initial value because the posi- tion has not sufficiently cooled while the second high-level degaussing signal is input. As shown in FIG. 2, the degaussing effect is applied when the second degaussing signal is input, since the AC current is attenuated by the high-resistance resistor as described above and then flows to the degaussing coil. There is a problem that is reduced.

Therefore, the present invention has been devised to solve the above-described problems, and the degaussing circuit of the monitor having excellent degaussing effect at a simpler and lower cost by constructing a degaussing circuit using an RLC resonant circuit. The purpose is to provide.

In order to achieve the above object, the circuit of the present invention generates a magnetic field when an alternating current flows and is turned by a degaussing coil for demagnetizing the magnetic field magnetized on the CRT, and a high level degaussing signal output from the microcomputer. A degaussing circuit of a monitor comprising a transistor configured to be turned on to cause an alternating current to be applied to the degaussing coil,

A diode which applies the alternating current to the degaussing coil after half-wave rectifying;

And a degaussing capacitor and a degaussing resistor connected in parallel to the degaussing coil, respectively.

1 is a circuit diagram showing a power supply system of a monitor including a conventional degaussing circuit;

FIG. 2 is a graph illustrating a problem when a continuous high level degaussing signal is input in the degaussing circuit of FIG.

3 is a circuit diagram illustrating a power system of a monitor including a degaussing circuit according to the present invention;

FIG. 4 is a graph illustrating a state in which the problem of when a continuous high level degaussing signal is input in the degaussing circuit of FIG. 3 is solved.

* Explanation of symbols for main parts of the drawings

200: degaussing circuit 201: micom

Q21: Transistor D21: Diode

L3: degaussing coil R21: degaussing resistor

C21: degaussing capacitor

Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

3 is a circuit diagram illustrating a power system of a monitor including a degaussing circuit according to the present invention.

As shown in FIG. 3, the degaussing circuit according to the present invention includes a micom 201 that outputs a degaussing signal and a transistor that is turned on when a high level degaussing signal is output from the micom 201. Q21, the diode Q21 is turned on and the AC current is inputted, and the diode D21 is applied to the degaussing coil L3 after half-wave rectification, and when the AC current is applied, A degaussing coil L3 for demagnetizing the magnet, a degaussing capacitor C21 and a degaussing resistor R21 connected in parallel to the degaussing coil L3, respectively.

Next, the operation and effect of the present invention configured as described above will be described in detail.

The microcomputer 201 outputs a high level degaussing signal in order to apply AC power to the degaussing coil L3 when a predetermined condition is reached, such as an initial state of turning on the power.

At this time, the high level degaussing signal is applied to the transistor Q21 through the resistors R11 and R12 and the capacitor C11 to turn on the transistor Q21, and thus the collector of the transistor Q21 is turned on. The stage and the emitter stage are short-circuited so that an alternating current of the power supply circuit is applied to the diode D21.

At this time, the diode (D21) is applied to the degaussing coil (L3) after half-wave rectifying the AC current, the resonance is made by the degaussing coil (L3) and degaussing capacitor (C21) As the attenuation is performed by the degaussing resistor R21, an alternating current of the attenuation vibration wave can be applied to the degaussing coil L3.

That is, as illustrated in FIG. 4, while a high level degaussing signal is input from the microcomputer 201, an alternating current of attenuated vibration wave is applied to the degaussing coil L3 to provide the degaussing coil ( L3) is capable of demagnetizing magnetized magnets in the CRT.

The present invention acting as described above can continuously obtain a good degaussing effect even if a continuous high level degaussing signal is input from the microcomputer 201 as shown in FIG. 4.

As described above, the present invention can obtain the AC current of the attenuated vibration wave by using the RLC resonant circuit, which facilitates the circuit configuration and reduces the unit cost, and continuously inputs the high level degaussing signal from the microcomputer. Even if it has an excellent degaussing effect can be obtained.

Claims (1)

When an alternating current flows, the degaussing coil L3 generates a magnetic field and demagnetizes the magnetic field magnetized on the CRT, and a high level degaussing signal output from the microcomputer turns on the alternating current to the degaussing coil. In the degaussing circuit of a monitor comprising and configured a transistor (Q21) to be applied, A diode D21 for half-wave rectifying the alternating current and applying the degaussing coil to the degaussing coil; And a degaussing capacitor (C21) and a degaussing resistor (R21) each connected in parallel to said degaussing coil.