Abstract:
An electric power source assembly supplies the focusing electrodes of a color cathode ray tube. Such a color cathode ray tube normally includes three electron guns arranged in a line transverse to their beam path. The focusing voltages supplied the focusing electrodes associated with the three guns are independently adjusted to compensate for beam distortion caused by positional differences in gun location. The D.C. and A.C. voltage to the static and or dynamic electrodes is independently controlled to improve beam focus of each individual gun.

Description:
FIELD OF THE INVENTION 
     This invention relates to an electric power source assembly for focusing electrodes of a color cathode ray tube apparatus, and more particularly to an improvement of the electric power source assembly for a Dynamic Beam Focus electrode (hereafter called DBF electrode). 
     BACKGROUND OF THE INVENTION 
     As well known, a color cathode ray tube apparatus using a shadow mask is usually provided with three electron gun assemblies of the in-line type, which produce self-converging beams by utilizing non-uniform deflecting magnetic fields. Such deflecting magnetic fields employ pin-cushion type magnetic field distribution horizontally and barrel type magnetic field distribution vertically. 
     This type of cathode ray tube, however, causes the distortion of the electron beam spot since the deflection is greater at the peripheral region of the screen than at the center, resulting in lowering of the screen resolution. 
     FIG. 7 illustrates an example of the DBF electrode used in the conventional cathode ray tube as shown in page 20 of January 1988 edition in Japanese periodical &#34;Television Technology&#34;. 
     In FIG. 7 the operation of the three focusing electrodes 10A, 10B, and 10C for Red, Green and Blue colors is illustrated. Each focusing electrode 10A, 10B, and 10C is divided into four segments respectively, to form a so called &#34;quadrupole lens&#34;, and two differing voltages are applied thereto. Namely, each focusing electrode 10A, 10B, 10C is formed by vertical electrodes (static electrodes) 1a1, 1a2, 1b1, 1a2, and 1c1, 1c2 and horizontal electrodes (dynamic electrodes) 2a1, 2a2, 2b1, 2b2 and 2c1, 2c2, so as to apply different voltages across the respective vertical and horizontal electrodes. 
     The electron beam 30 is emitted from the cathode 28 of the electron gun and is focused by the focusing electrode 10B to make the beam spot 31 for the green color on the screen. Likewise, electron beams are also emitted from the cathodes 27 and 29 of the other electron guns and deflected by the focusing electrodes 10A and 10C to make the other beam spots (not shown). 
     FIG. 8 illustrates a circuit for applying voltages to the focusing electrodes 10A, 10B and 10C shown in FIG. 7. In FIG. 8, the dynamic electrodes 2a1, 2a2, 2b1, 2b2, 2c1, and 2c2 are supplied AC voltage ΔV by AC power source 4 through lines 11 to 16 connected between coupling condenser 3 and the earth E. The AC voltage ΔV is superimposed on DC voltage Efa formed by dividing a supply voltage from DC power source FBT using variable resistor 5. 
     The static electrodes 1a1, 1a2, 1b1, 1b2, 1c1, and 1c2, on the other hand, are supplied DC voltage Efb through lines 17 to 110. DC voltage Efb is divided from the supply voltage from DC power source FBT by using a variable resistor 6 through which the power source FTB is applied. 
     The electron beams are emitted by three electron guns arranged in line with each other, and are deflected or focused by the deflecting magnetic field generated by means of a yoke coil (not shown in the drawing). The deflecting magnetic field is non-uniformly distorted both vertically and horizontally as explained above, thereby performing self-convergence of the three electron beams. 
     Conventional color cathode ray tube apparatus of the self-convergence type, however, exhibit a problem in that defocus of the electron beam spot occurs due to the deflection increases at the peripheral region of the screen, causing the resolution of the screen in these areas to be reduced. This phenomenon is caused by the fact that the electron beams deflected by the self-convergence type deflecting yoke generate an astigmatism based on the lens function due to the deflecting operation. 
     In order to cancel the astigmatism, techniques for performing beam deformation before the electron beam is deflected by the deflecting yoke are known; that is, the beam deformation is achieved by controlling the voltage potential of the dynamic electrodes 2a1, 2a2, 2b1, 2b2 and 2c1, 2c2, and the static electrodes 1a1, 1a2, 1b1, 1b2 and 1c1, 1c2 individually. 
     The static electrodes 1a1, 1a2, 1b1, 1b2 and 1c1, 1c2 have a strong forming controllability mainly along the x-axis of the beam spot, while the dynamic electrodes 2a1, 2a2, 2b1, 2b2 and 2c1, 2c2 have a strong forming controllability mainly along the y-axis of the beam spot. Consequently, the beam defocus in a single beam, may be canceled by properly controlling the static electrode voltage against horizontal defocusing and the dynamic electrode voltage against vertical defocusing to get correct focusing. 
     In the conventional color cathode ray tube apparatus, however, because the static electrode voltage and dynamic electrode voltage are commonly applied to each electrode 10A, 10B and 10C through only two common lead lines Lh, Lv as explained above, it has been found that beam defocus was not completely canceled, due to the positional discrepancy between the plural electron guns arranged in a horizontal line. This positional discrepancy causes different magnetic field deflection from gun to gun. In other words, the positional discrepancy causes the deflection yoke to perform different lens functions on the R,G, and B beams. 
     In more detail, in a case in which the G beam is standardized, the R beam results in overfocusing at the right side of the screen (in front view), and in underfocusing at the left side. On the other hand, the B beam results in underfocusing at the right side of the screen and overfocusing at the left side. As used herein, overfocusing means insufficient dynamic voltage, and underfocusing means excessive dynamic voltage. This unavoidable phenomenon could not heretofore be corrected as if either one of the R,G,B guns was focused accurately, the other guns were inevitably even more defocused. 
     Moreover, the above tendency was further promoted by the scattering in manufacturing of the electron gun. It was, therefore, very difficult for all R,G,B beams to be correctly focused at the full area of the screen. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to provide a color cathode ray tube apparatus capable of controlling the R,G,B beams independently to get correct focusing of all beams. 
     Another object of the invention is to provide an electric power source assembly for focusing electrodes of the color cathode ray tube apparatus. 
     A further object is to provide an electric power source assembly for the DBF electrodes capable of controlling independently either or both focusing components in Y-axis direction or X-axis direction of each of the R,G,B beams. 
     A still another object of the invention is to provide an electric power source assembly for the DBF electrodes capable of controlling independently both outer beams of R,G,B guns and the center beam thereof in either or both of the Y-axis direction and X-axis direction. 
     These and other objects of the present invention will become more fully apparent from the detailed description presented hereinbelow and the attached drawings which are illustrative of preferred embodiments of the present application. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram showing an electric power source assembly for focusing electrodes of a color display monitor of a first embodiment of the invention. 
     FIGS. 2 to 6 are schematic diagrams of second to sixth embodiments of the present invention, respectively, showing an electric power source assembly for focusing electrodes of a color display monitor. 
     FIG. 7 is a schematic drawing for explaining the operation of focusing electrodes of a prior art color display monitor. 
     FIG. 8 is a circuit diagram showing a conventional electric power source assembly for focusing electrodes of a color display monitor. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Various embodiments of the present invention will be described below with reference to the accompanying drawings wherein like elements in plural figures bear like reference numerals. 
     FIG. 1 is a schematic diagram showing a circuit configuration in the first embodiment of the focusing electrodes of a color display monitor. 
     Referring to FIG. 1, each focusing electrode set 10A, 10B and 10C for red, green and blue color (R,G,B), respectively, is formed by static electrodes 1a1, 1a2, 1b1, 1a2, and 1c1, 1c2 and dynamic electrodes 2a1, 2a2, 2b1, 2b2 and 2c1, 2c2. The static electrodes 1a1, 1a2, 1b1, 1b2, 1c1, 1c2 are commonly supplied DC voltage Efb through lines 17 to 110. DC voltage Efb is divided from the supply voltage developed by DC power source FBT by using a variable resistor 6 through which the supply voltage form the power source FTB is applied in a manner similar to that of FIG. 7. 
     On the other hand, the dynamic electrodes 2a1, 2a2, 2b1, 2b2, 2c1, and 2c2 are applied AC voltage ΔV by an AC power source 4 via coupling condensers 3a, 3b and 3c superimposed on DC voltages Efa1, Efa2 and Efa3. DC voltage Efa1, Efa2 and Efa3 are respectively divided by variable resistors 5a, 5b and 5c from the supply voltage obtained from DC power source FBT. In operation, three DC voltages Efa, Efb and Efc are separately applied to DBS electrodes 10A, 10B and 10C through lines 11, 12, 13, 14 and 15, 16, respectively. 
     Upon adjusting each variable resistor 5a, 5b and 5c, DC voltage applied to each dynamic electrode 2a (2a1, 2a2), 2b (2b1, 2b2) and 2c (2c1, 2c2) is independently controlled so that each beam R,G,B is focused to an optimum position, respectively. This embodiment enables, therefore, Y direction components of all R,G,B beams to be correctly focused over all areas of the screen. 
     FIG. 2 illustrates a second embodiment of the present invention. The reference numerals in FIG. 2 that are identical to those in FIG. 1 represent identical or similar parts to those in FIG. 1. The second embodiment differs from the first embodiment in the configuration of the AC voltage sources 4a, 4b and 4c. 
     In FIG. 2, the AC voltage sources 4a, 4b and 4c are capable of being controlled to independently vary the value of their voltages, respectively. This embodiment also enables, therefore, Y direction components of all R,G,B beams to be correctly focused over all areas of screen with even more accuracy. 
     FIG. 3 illustrates a third embodiment of the invention. 
     Referring to FIG. 3, the AC power source 4 and DC voltage Efa divided from DC power source FBT by variable resistor 5 are superimposedly applied to each dynamic electrodes 2a (2a1, 2a2), 2b (2b1, 2b2), 2c (2c1, 2c2) through lines 11 to 16. 
     However, static electrodes 1a (1a1, 1a2), 1b (1b1, 1b2), 1c (1c1, 1c2) are separately applied DC voltages Efb1, EFb2 and Efb3 through lines 111 to 116, which DC voltages Efb1, Efb2 and Efb3 are respectively divided by variable resistors 6a, 6b and 6c from the supply voltage of the power supply FBT. 
     The third embodiment differs from the first and second embodiments in configuration in that the DC voltage applied to each static electrode 1a (1a1, 1a2), 1b (1b1, 1b2) and 1c (1c1, 1c2) is independently controlled instead of those voltages supplied to the dynamic electrodes. Therefore, upon adjusting each variable resistor 6a, 6b and 6c, each beam R,G,B is focused on an optimum position, respectively. 
     This embodiment enables, therefore, X-direction components of all R,G,B beams to be correctly focused over all areas of the screen. 
     The third embodiment can be modified by combining with the first or second embodiment as shown in FIG. 4 and FIG. 5. 
     FIG. 4 illustrates a fourth embodiment which is a combination of the second and third embodiments, and FIG. 5 illustrates a fifth embodiment which is a combination of the first and third embodiments. 
     The operation is self-explanatory, therefore, it is easily understood that these embodiments enable, both X and Y-direction components of all R,G,B beams to be correctly focused over all areas of the screen. 
     Finally, FIG. 6 illustrates a sixth embodiment of this invention. In FIG. 6, the static electrodes 1a1, 1a2, 1c1, 1c2 are supplied DC voltage Efb1 through lines 111, 112 and 115, 116. Common DC voltage Efb1 is divided by a variable resistor 6d to which the supply voltage from power source FTB is applied, while the static electrodes 1b1, 1b2 are supplied DC voltage Efb2 through lines 113, 114; DC voltage Efb2 being divided by a variable resistor 6b from the supply voltage from power source FTB. 
     On the other hand, the dynamic electrodes 2a1, 2a2 are supplied the superimposed voltage of AC power source 4d and DC voltage Efa1 through lines 11, 12. This voltage is developed by dividing the supply voltage from power source FTB by variable resistor 5d. The dynamic electrodes 2b1, 2b2 are supplied a superimposed voltage of AC power source 4b and DC voltage Efa2 through lines 13, 14. This voltage is developed by dividing the supply voltage from the power source FTB by variable registers 5b. Further, the dynamic electrodes 2c1, 2c2 are supplied DC voltage Efa1 through lines 15, 16. DC voltage Efa1 is developed by dividing the supply voltage from the power source FTB divided by variable resistor 5d. 
     The sixth embodiment differs from the fourth embodiment in configuration in that DC voltage Efa1 applied to the dynamic electrodes 2a (2a1, 2a2) and 2c (2c1, 2c2) are commonly provided, and DC voltage Efb1 applied the static electrodes la (1a1, 1a2) and lc (1c1, 1c2) is commonly provided. 
     Those connections would also make sense in practice by the reason that there is a tendency for deflecting or focusing errors at the both ends R and B to be similar to each other, because, as described in FIG. 7, the focusing electrodes 10A, 10B and 10C for R,G,B and the electron guns 27, 28 and 29 for R,G,B are arranged in line, respectively. 
     The sixth embodiment is capable of reducing the number of parts and getting a smaller size in the assembly compared with the forth embodiment. 
     In the above explanation on the sixth embodiment, the dynamic electrodes 2a, 2c and the static electrodes 1a, 1c are commonly controlled, respectively. However, it is possible, of course, to commonly control only either the dynamic electrodes 2a, 2c or the static electrodes 1a, 1c. 
     Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.