JPH0676988U - Dynamic focus circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] To prevent electron beam hocus shift due to increase in electron beam pulsing current. [Structure] The focus drive circuit 12 has a horizontal pulse b.
1 and the vertical pulse c1, a parabolic signal is created, and the video signal a1 is cut off at a predetermined cutoff point to create a video signal correction signal. The video signal correction signal is superimposed on the parabolic signal to focus drive signal d1. To create the primary winding L1 of the focus drive transformer 13
1 is supplied to one end. As a result, it is possible to prevent deviation of the hocus of the electron beam due to an increase in the electron beam current.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a dynamic focus circuit used in a shadow mask type picture tube such as a color television receiver or a color monitor, and particularly to a dynamic focus circuit capable of suppressing a hocus shift due to a video signal.

[0002]

[Prior art]

 Generally, in a television receiver equipped with a shadow mask type picture tube, the focus voltage of three electron beams is adjusted so that the electron beam passing through the holes of the shadow mask is accurately focused on the phosphor and landed. Is set.

FIG. 4 is a cross-sectional view showing the outline of the inside of a conventional shadow mask type picture tube seen from above.

In FIG. 4, the shadow mask type picture tube 50 forms a panel surface 53 having a predetermined curvature through a funnel portion 52 that expands at a predetermined angle from a neck portion 51 having a small diameter. R (red), G (green), and B (blue) three-color electron guns 54R, 54G, and 54B are arranged on the neck portion 51 by a predetermined arrangement method.

Further, an electromagnetic deflection component such as a color purity adjusting magnet or a deflection yoke is provided on the outer side from the neck portion 51 to the funnel portion 52, and the red electrons emitted from the electron guns 54 R, 54 G, 54 B are emitted. The beam 55R, the green electron beam 55G, and the blue electron beam 55B are deflected around the deflection center 61 of the deflection yoke.

On the other hand, on the back surface side of the panel surface, a large number of phosphors 56 are formed in a film shape corresponding to the three-color electron beams 55R, 55G, and 55B, with three colors as one set. Then, a shadow mask 57 is attached by a pin 60 via a frame 59 to the electron gun side by a predetermined distance from the surface of these phosphors 56. The shadow mask 57 has a number of holes 58 corresponding to the number of the phosphors 56.

FIG. 5 is a front view showing the shadow mask type picture tube of FIG.

In FIG. 5, the shadow mask type picture tube 50 has a structure in which it is attached to the lug 63 via a vibration-proof band 62.

In the screen 64 of the shadow mask type picture tube 50, the distance DH from the center to the left edge is 4/3 times the distance DV from the center to the upper edge. The distance DHV from the center to the four corners is 5/3 times the distance DV from the center to the upper edge.

FIG. 6 is an explanatory view showing the focus of such a conventional shadow mask type picture tube, and explains the green electron beam 55G.

In general, the hocus voltage of the shadow mask type cathode-ray tube 50 is such that when the green electron beam 55 G irradiates the center of the screen 64, the focus matches the phosphor 56 in the center of the screen 64. Is set to a constant value. The spot 65 is an image when the green electronic beam 55G is applied to the center of the screen 64.

However, since the locality of the phosphor screen 66 of the shadow mask type picture tube 50 on which the phosphor 56 is formed and the locality of the hocus plane 67 of the green electron beam 55G are different, the green electron beam 55G is When the periphery of the screen 64 is irradiated, the distance D11 from the deflection center 61 to the focus surface 67 becomes shorter than the distance D12 from the deflection center 61 to the fluorescent screen 66, and the green electron beam 55G is emitted. The inside of the fluorescent screen 66 is invisible. As a result, the amount of light emitted by the phosphor 56 is reduced, or the phosphor 56 is radiated onto another phosphor to enlarge the image as shown by the spot 68, and the sharpness, resolution and contrast of the image are reduced. I will let you. Such reductions in sharpness, resolution, and contrast at the periphery of the screen are the same for red and blue electron beams.

Such a decrease in sharpness, resolution and contrast does not cause much problem in a shadow mask type picture tube having a small screen because the difference between the distance between the hocus position and the phosphor at the peripheral portion of the screen is small. In a large-sized shadow mask type picture tube, there is a large difference in the distance between the hocus position and the phosphor in the peripheral part of the screen, which makes it quite noticeable.

In response to this, there is a large-sized shadow mask type picture tube in which a parabola voltage is superimposed on a constant DC voltage by a dynamic focus circuit to create a focus voltage.

FIG. 7 is a waveform diagram showing the hocus voltage output by such a dynamic hocus circuit separately in the case of vertical polarization and in the case of horizontal polarization. FIG. 7A shows the hocus voltage VFV2 in the case of vertical polarization. 7B shows the focus voltage VFH2 in the case of horizontal deflection.

In the case of vertical deflection, the hocus electric power VFV2 is a DC voltage VDC2 (about 8,000 V) set manually, and a parabola voltage VPV2 synchronized with a vertical synchronizing signal with a period of one vertical synchronizing period (1 V) is superimposed. It is the combined voltage. The amplitude DPV 2 of the parabolic voltage is set from 200V to 300V.

The hocus voltage VFH2 in the case of horizontal deflection is a voltage obtained by superimposing a direct current voltage VDC2 set manually and a parabolic voltage VPH2 synchronized with a horizontal synchronizing signal having a period of one horizontal synchronizing period (1H). . The parabolic voltage amplitude DPH2 is set from 1000V to 1500V.

In the shadow mask type picture tube using such a dynamic focus circuit, the fluorescence of the shadow mask type picture tube is used when the brightness is constant over the entire screen, that is, when the transfer current by the electron beam is constant. It is possible to exactly match the locality of the plane with the locality of the hocus plane of the electron beam to accurately land the electron beam on the phosphor. However, if the transfer current of the electron beam changes due to the change in the brightness of the video signal, the hocus plane of the electron beam shifts.

FIG. 8 is an explanatory diagram for explaining the deviation of the hocus of the electron beam due to such a current of the electron beam. FIG. 8A shows the case where the current of the electron beam is small, and FIG. The case where the current is large is shown.

In FIG. 8, when the transfer current of the electron beam 55G is small, as shown in FIG. 8A, the hocus position of the electron beam 55G is only slightly displaced forward of the fluorescent screen 66. Although the spot 71 due to the electron beam 55G becomes a small image, when the electron beam 55G has a large shunt current, the hocus position of the electron beam deviates largely ahead of the fluorescent screen 66, as shown in FIG. 8B. The spot 72 formed by the electron beam 55G becomes a large image.

FIG. 9 is a graph showing the transfer current Ikp2 of such an electron beam and the area S2 of the spot due to the electron beam. The horizontal axis shows the transfer current Ikp2 and the vertical axis shows the area S2 of the spot due to the electron beam. Is shown.

As shown in FIG. 9, the area S2 of the spot by the electron beam rises in a quadratic curve corresponding to the electron beam transfer current Ikp2, and the image displayed on the screen is high. In the case of the brightness state, the image displayed on the screen has a low sharpness, resolution and contrast.

[0023]

[Problems to be solved by the device]

 In such a conventional dynamic focus circuit, when the brightness of the video signal rises and the electron beam transfer current increases, the hocus point of the electron beam is located in front of the phosphor and is displayed on the screen. The resulting image has a low sharpness, resolution and contrast.

An object of the present invention is to eliminate the above-mentioned problems and to provide a dynamic focus circuit capable of preventing the hocus shift of the electron beam when the brightness of the video signal is increased and the electron beam transfer current is increased. .

[0025]

[Means for Solving the Problems]

 The dynamic focus circuit according to the present invention is a dynamic focus circuit that creates a hocus voltage for causing a shadow mask type picture tube to dynamically focus an electron beam. And a parabolic signal synchronized with the vertical sync signal, and a video signal correction signal is created by cutting off the input video signal at a predetermined cutoff point, and the video signal correction signal is superimposed on the parabolic signal. A focus drive circuit that creates a focus drive signal and a focus drive signal that is oscillated when the focus drive signal from this focus drive circuit is supplied to the primary winding, and outputs a hocus voltage correction voltage from the secondary winding. From the transformer and this focus drive transformer And feature by comprising a voltage superimposing means for creating said Hocus voltage by superimposing a carcass voltage correction voltage into a DC voltage from the DC power supply circuit.

[0026]

[Action]

 With this configuration, the focus drive circuit cuts off the input video signal at a predetermined cutoff point to create a video signal correction signal, and the video signal correction signal created on the parabolic signal is superimposed on the focus signal. Since the drive signal is created and the voltage superimposing means superimposes the hocus voltage correction voltage from the focus drive transformer oscillated by the focus drive signal on the DC voltage from the DC power supply circuit, the hocus voltage is created. It is possible to prevent the hocus shift of the electron beam when the brightness of the electron beam is increased and the electron beam transfer current is increased.

[0027]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of a dynamic focus circuit according to the present invention, which is applied to a dynamic focus circuit used in a shadow mask type picture tube of a primary color drive system.

In FIG. 1, a horizontal winding pulse voltage Vp is introduced to the primary winding L1 of the flyback transformer 11. A plurality of rectifying diodes D11, D12, D13 are inserted in the secondary winding L2 of the flyback transformer 11, and these rectifying diodes D11, D12, D13 and the shadow mask type cathode ray tube are connected to each other. And the stray capacitance generated in the fourth grid rectifies the pulse voltage generated in the secondary winding L2 and rectifies the high voltage VH (from 20 kV to the anode of the shadow mask type picture tube and the fourth grid). 30 kV). The other end of the secondary winding L2 is connected to a reference potential point via a capacitor C11 and is also connected to an ABL (automatic brightness limiting) circuit.

Further, the connection point between the cathode of the rectifying diode D11 and the secondary winding L2 is connected to the reference potential point via the series connection of the resistor R11 and the variable resistor VR1. The sliding contact of the variable resistor VR1 is connected to the reference potential point. As a result, a desired DC voltage (approximately 8,000 V) VDC1 can be obtained at the connection point A1 between the resistor R11 and the variable resistor RV1 by adjusting the sliding contact of the variable resistor VR1.

On the other hand, the focus drive circuit 12 is supplied with the composite video signal a1, the horizontal pulse b1 and the vertical pulse c1 from the input terminals 21, 22 and 23, respectively. The focus drive circuit 12 creates a parabolic signal from the horizontal pulse b1 and the vertical pulse c1 and cuts off the composite video signal a1 at a predetermined cutoff point to create a video signal correction signal. Is superimposed on the parabolic signal to create a focus drive signal d1 and supplied to one end of the primary winding L11 of the focus drive transformer 13. The other end of the primary winding L11 is connected to the reference potential point. The secondary winding L12 of the focus drive transformer 13 has one end connected to a reference potential point and the other end connected to a connection point A2 via a capacitor C12. The connection point A2 is connected to the connection point A1 and the third grid of the shadow mask type picture tube. With such a connection, the capacitor C12 and the connection point A2 form a voltage superimposing means.

The focus drive transformer 13 is oscillated by the focus drive signal d1 and outputs a focus correction voltage VFA1 obtained by combining the parabola voltage and the video signal correction voltage from the secondary winding L12. Such a focus correction voltage VFA1 is superposed on the DC voltage VDC1 at the connection point A2 via the capacitor C12 and is guided to the third grid of the shadow mask type picture tube as the focus voltage VF1.

FIG. 2 is an explanatory diagram showing an electron gun used for a shadow mask type picture tube to which the focus correction voltage VF1 from the dynamic focus circuit of FIG. 1 is supplied.

The electron gun 30 uses a common lens type in which the first to fourth grids 41, 42, 43, 44 are common to the three-color cathodes 31R, 31G, 31B. First to fourth grids 41, 42, 43, 44 are arranged on the front side of the three-color cathodes 31R, 31G, 31B. The first grid 41 acts as a control electrode and controls the amount of electron beam from the cathodes 31R, 31G, 31B. The second grid 42 is an accelerating electrode and accelerates the electron beam. The third and fourth grids 43 and 44 generate the focus lens 45 between them, and the focus voltage VF1 is supplied to the third grid 43 and the high voltage VH is supplied to the fourth grid 43.

The electron beams generated from the three-color cathodes 31R, 31G, and 31B are accelerated and converged by the first to fourth grids 41, 42, 43, and 44, and irradiated on the phosphor.

FIG. 3 is a waveform diagram showing the operation of such an embodiment. FIG. 3 (a) shows the composite video signal a1, FIG. 3 (b) shows the electron beam transfer current Ikp1, and FIG. 3 (c) indicates the focus voltage VF1.

The composite video signal a1 supplied to the focus drive circuit 12 has a horizontal synchronizing signal S1 in the blanking period and a video signal component V1 in the scanning period. The focus drive circuit 12 creates a parabolic signal from the horizontal pulse b1 and the vertical pulse c1 and cuts off from the composite video signal a1 shown in FIG. 3 (a) at a predetermined cutoff point Vc. Create a correction signal. This video signal correction signal matches the level-adjusted waveform of the transfer current Ikp1 shown in FIG. 3 (b). The focus drive circuit 12 superimposes the video signal correction signal on the parabolic signal to create a focus drive signal d1 and supplies it to the focus drive transformer 13. As a result, the focus drive transformer 13 outputs the focus correction voltage VFA1 obtained by combining the parabola voltage and the video signal correction signal corresponding to the transfer current Ikp1 from the secondary winding L12. Such a focus correction voltage VFA1 is combined with the DC voltage VDC1 at the connection point A2 via the capacitor C12, and is guided to the third grid 43 of the shadow mask type picture tube as the focus voltage VF1 shown in FIG. 3C. The focus voltage VF1 in this case is the direct current voltage VDC1 manually set, the parabolic voltage P1 synchronized with the horizontal synchronizing signal, and the video signal component cut off at the cutoff point Vc in FIG. 3 (a). The voltage V2 based on V1 is a superimposed voltage. Although not shown, the parabolic voltage synchronized with the vertical synchronizing signal is also superimposed on the focus voltage VF1.

According to this embodiment, when the luminance of the composite video signal a1 is increased and the electron beam transfer current from the three-color cathodes 31R, 31G, and 31B of the electron gun 30 is increased, , The hocus voltage VF1 is lowered to prevent the hocus point from moving to the outside of the screen. This will prevent the amount of light emitted by the phosphors from decreasing and prevent the phosphors from being spread on other phosphors to enlarge the image, and improve the sharpness, resolution and contrast of the image. You can

In the embodiment of FIG. 1, the focus drive circuit 12 uses the composite video signal a1 as the video signal for creating the focus drive signal d1, but the video for creating the focus drive signal d1 is used. As the signal, one of the three primary color signals after the color signal processing may be used. Further, in the embodiment of FIG. 1, the invention is applied to the dynamic focus circuit used in the shadow mask type picture tube of the primary color drive system, but it is also applied to the dynamic focus circuit used in the shadow mask type picture tube of the color difference drive system. Good.

[0040]

[Effect of device]

 According to the present invention, it is possible to prevent the hocus shift of the electron beam when the brightness of the video signal rises and the electron beam transfer current increases, so that the amount of light emitted by the phosphor decreases, and It is possible to prevent the image from being enlarged due to the rudder on the phosphor, and to improve the sharpness, resolution and contrast of the image.

[0041]

[Brief description of drawings]

[0042]

FIG. 1 is a circuit diagram showing an embodiment of a dynamic focus circuit according to the present invention.

[0043]

FIG. 2 is an explanatory diagram showing an electron gun to which a focus correction voltage is supplied from the dynamic focus circuit of FIG.

[0044]

3 is a waveform chart showing the operation of the embodiment of FIG.

[0045]

FIG. 4 is a cross-sectional view seen from above showing the inside of a conventional shadow mask type picture tube.

[0046]

5 is a front view showing the shadow mask type picture tube of FIG. 4. FIG.

[0047]

6 is an explanatory view showing the focus of the shadow mask type picture tube of FIG.

[0048]

FIG. 7 is a waveform diagram showing a hocus voltage output from a conventional dynamic hocus circuit.

[0049]

FIG. 8 is an explanatory diagram for explaining a shift of a hocus of an electron beam due to a transfer current of a shadow mask type picture tube using a conventional dynamic hocus circuit.

[0050]

FIG. 9 is a graph showing a relationship between a transfer current of a shadow mask type picture tube using a conventional dynamic focus circuit and an area of a spot by an electron beam.

[0051]

[Explanation of symbols]

 11 Flyback transformer 12 Focus drive circuit 13 Focus drive transformer A2 Connection point C12 Capacitor

Claims (1)

[Scope of utility model registration request] 1. A dynamic focus circuit for creating a hocus voltage for dynamically focusing an electron beam on a shadow mask type picture tube, comprising: a DC power supply circuit for outputting a DC voltage; and a horizontal and vertical sync signal. A parabola signal is generated, and a video signal correction signal is created by cutting off the input video signal at a predetermined cutoff point, and the video signal correction signal is superimposed on the parabola signal to create a focus drive signal. A focus drive circuit, a focus drive transformer that oscillates when a focus drive signal from this focus drive circuit is supplied to the primary winding, and outputs a hocus voltage correction voltage from the secondary winding, and a focus drive transformer from this focus drive transformer. The DC voltage of the hocus voltage correction voltage Dynamic focus circuit, characterized by comprising a voltage superimposing means for creating said Hocus voltage by superimposing on a DC voltage from the road.