Cathode-ray tube display unit in which unwanted radiant electric field from face plate of cathode-ray tube is decreased

• US 5,689,157 A
• Filed: 10/18/1995
• Issued: 11/18/1997
• Est. Priority Date: 05/08/1992
• Status: Expired due to Fees

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Kawakami, Katsuyuki, Yoshioka, Hiroshi, Satoh, Yoshio, Sakurai, Soichi, Jitsukata, Hiroshi
• Primary Examiner(s): Issing, Gregory C.
• Application Number:
  US08/544,923
• Time in Patent Office: 762 Days
• Field of Search: 315/8, 315/85, 315/370, 313/479, 348/818, 348/819, 348/820
• US Class Current: 315/370
• CPC Class Codes: H01J 2229/0015 Preventing or cancelling fields leaving the enclosure
• CPC Class Codes: H01J 29/003 Arrangements for eliminating unwanted electromagnetic effects, e.g. demagnetisation arrangements, shielding coils H01J29/06, H01J29/867 take precedence; demagnetisation in general H01F13/00; circuit arrangements therefor H04N9/29; screening of apparatus against electric or magnetic fields H05K9/00

Abstract

A cathode-ray tube display unit provided with a high voltage transformer for supplying high voltage to an anode of a cathode-ray tube, a deflection yoke having a horizontal deflection coil and a vertical deflection coil, and an interior conductive coating formed on the inside of a glass vessel of the cathode-ray tube, in which there is provided an electrode in the conductive coating form formed on an external wall face of a glass vessel at a funnel portion being electrically separated from an exterior graphite coating formed on an external surface of the cathode-ray tube and connected to ground, and a circuit for applying reverse pulse voltage V₁ that satisfies (V₀ ×C₀)>(V₁ ×C₁) to the electrode in the conductive coating form is included. Where, it is assumed that flyback pulse voltage supplied to the deflection yoke means is V₀, reverse pulse voltage having a polarity reverse to that of voltage generated in the interior conductive coating is V₁, electrostatic capacity between the horizontal deflection coil and the interior conductive coating is C₀, and electrostatic capacity between the electrode in the conductive coating form and the interior conductive coating is C₁.

Claims

1. A cathode-ray tube display unit comprising:

voltage supplying means for supplying at least a high voltage to an anode of a cathode-ray tube;

deflection yoke means having a horizontal deflection coil and a vertical deflection coil;

an interior conductive coating formed on the inside of a glass vessel of said cathode-ray tube;

a conductive film electrode formed on an external wall surface of the glass vessel of a funnel portion of the cathode-ray tube, said conductive film electrode being electrically separated from an exterior graphite coating formed on an external wall surface of said cathode-ray tube, said exterior graphite coating being electrically connected to ground; and

means connected to said conductive film electrode for generating a reverse pulse voltage V₁ having a polarity reverse to that of a voltage generated in said interior conductive coating due to an electrostatic coupling generated by a flyback pulse voltage V₀ supplied to said deflection yoke means, wherein a value of said reverse pulse voltage V₁ is set so that an equation V₀₁ -V₁₁ ≈

0 is satisfied, where V₀₁ is a first alternating voltage proportional to a product (V₀ ×

C₀), C₀ is an electrostatic capacity between said horizontal deflection coil and said interior conductive coating, V₁₁ is a second alternating voltage proportional to a product (V₁ ×

C₁), and C₁ is an electrostatic capacity between said conductive film electrode and said interior conductive coating means.

2. A cathode-ray tube display unit according to claim 1, wherein said means for generating the reverse pulse voltage includes:

means for detecting a flyback pulse generated in said horizontal deflection coil; and

means for attenuating and inverting said detected flyback pulse so as to obtain the reverse pulse voltage.

3. A cathode-ray tube display unit according to claim 1, wherein a thickness of glass of the glass vessel at a portion adjacent said horizontal deflection coil is formed thicker than other portions of the cathode-ray tube so as to reduce said electrostatic capacity C₀.

4. A cathode-ray tube display unit according to claim 1, wherein said interior conductive coating is formed in a predetermined area of the glass vessel so as to reduce said electrostatic capacity C₀.

5. A cathode-ray tube display unit according to claim 1, wherein a dielectric constant of a glass material of a portion of the glass vessel adjacent said horizontal deflection coil is set to 8 or below so as to reduce said electrostatic capacity C₀.

6. A cathode-ray tube display unit according to claim 1, wherein, a relationship of 0.5≦

(C₁ /C₀)≦

15 is satisfied.

7. A cathode-ray tube display unit according to claim 1, further comprising a transparent conductive coating formed on an external surface of a face plate of said cathode-ray tube and connected to ground.

8. A cathode-ray tube display unit according to claim 7, wherein said transparent conductive coating includes a resistance having a resistance value per unit area at 2×

10⁶ Ω

/square! or below.

9. A cathode-ray tube display unit according to claim 1, wherein said means for generating the reverse pulse voltage includes means for obtaining reverse pulse voltage from an auxiliary winding provided on a core of said deflection yoke.

10. A cathode-ray tube display unit comprising:

voltage supplying means for supplying at least a high voltage to an anode of a cathode-ray tube;

deflection yoke means having a horizontal deflection coil and a vertical deflection coil;

an interior conductive coating formed on the inside of a glass vessel of said cathode-ray tube;

a conductive film electrode, formed on an external wall surface of the glass vessel of a funnel portion of the cathode-ray tube, said conductive film electrode being electrically separated from an exterior graphite coating formed on an external wall surface of said cathode-ray tube, said exterior graphite coating being electrically connected to ground; and

means connected to said conductive film electrode for generating a reverse pulse voltage V₁ having a polarity reverse to that of a voltage generated in said interior conductive coating due to an electrostatic coupling generated by a flyback pulse voltage V₀ to said deflection yoke means;

wherein a value of said reverse pulse voltage V₁ is set so that an equation V₀₁ -V₁₁ ≈

0 is satisfied, where V₀₁ is a first alternating voltage proportional to a product (V₀ ×

C₀), C₀ is an electrostatic capacity between said horizontal deflection coil and said interior conductive coating, V₁₁ is a second alternating voltage proportional to a product (V₁ ×

C₁), and C₁ is an electrostatic capacity between said conductive film electrode and said interior conductive coating; and

wherein an intensity of a very low frequency electric field (VLEF) is decreased to a value no greater than 1 (V/m) at a distance of about 30 cm from and in front of a front surface of said cathode-ray tube.

11. A cathode-ray tube display unit comprising:

voltage supplying means for supplying high voltage to an anode of a cathode-ray tube;

deflection yoke means having a horizontal deflection coil and a vertical deflection coil;

an interior conductive coating formed on the inside of a glass vessel of said cathode-ray tube;

a conductive film electrode formed on an external wall surface of a glass vessel of a funnel portion of the cathode-ray tube, said conductive film electrode being electrically separated from an exterior graphite coating formed on an external wall surface of said cathode-ray tube, said exterior graphite coating being electrically connected to ground; and

means for generating a first reverse pulse voltage V₁ having a polarity reverse to that of voltage generated in said interior conductive coating due to an electrostatic coupling generated by a flyback pulse voltage V₀ supplied to said deflection yoke means;

means for generating a second reverse pulse voltage V₃ having a polarity inverted from that of A.C. components generated at an output of said voltage supplying means;

means for adding said first reverse pulse voltage V₁ and said second reverse pulse voltage V₃ to each other; and

means for supplying an output of said adding means to said conductive film electrode, wherein an electrostatic capacity between said horizontal deflection coil and said interior conductive coating means is C₀ and an electrostatic capacity between said conductive film electrode and said interior conductive coating is C₁, and the relationship (V₀ ×

C₀)>

((V₁ +V₃)×

C₁) is satisfied.

12. A cathode-ray tube display unit comprising:

high voltage transformer means for supplying at least a high voltage to an anode of a cathode-ray tube;

deflection yoke means having a horizontal deflection coil and a vertical deflection coil;

an interior conductive coating formed on the inside of a glass vessel of said cathode-ray tube;

means for generating a first reverse pulse voltage having a polarity inverted from that of flyback pulse voltage generated in said horizontal deflection coil;

means for supplying said first reverse pulse voltage to said interior conductive coating through an electrostatic capacity;

means for generating a second reverse pulse voltage having a polarity inverted from that of A.C. components generated at an output terminal of said high voltage transformer means;

means for adding said first reverse pulse voltage and said second reverse pulse voltage to each other; and

means for supplying an output of said adding means to said interior conductive coating through the electrostatic capacity.

13. A cathode-ray tube display unit according to claim 12, wherein said means for generating the first reverse pulse voltage includes:

means for detecting the flyback pulse generated in said horizontal deflection coil; and

means for attenuating and inverting said detected flyback pulse so as to obtain the first reverse pulse voltage.

14. A cathode-ray tube display unit according to claim 12, wherein said means for generating at least one of the first and second reverse pulse voltage includes transformer means in which a primary winding thereof is connected to said horizontal deflection coil and at least one of the first and second reverse pulse voltage is obtained from a secondary winding.

15. A cathode-ray tube display unit according to claim 12, wherein means for generating at least one of the first and second reverse pulse voltage includes means for obtaining at least one of the first and second reverse pulse voltage from an auxiliary winding provided on a core of said deflection yoke.

16. A cathode-ray tube display unit according to claim 12, wherein said means for supplying the first reverse pulse voltage includes means for applying said first reverse pulse voltage through a capacitor connected at one end output terminal of said high voltage transformer means at one end thereof.

17. A cathode-ray tube display unit according to claim 12, wherein said means for supplying the first reverse pulse voltage includes means for applying said first reverse pulse voltage through a capacitor connected at one end thereof to an anode button portion for leading high voltage from said high voltage transformer means to an anode of a cathode-ray tube.

18. A cathode-ray tube display unit according to claim 12, wherein said means for supplying the first reverse pulse voltage includes means for applying said first reverse pulse voltage through a conductor provided coaxially around an anode cable for leading high voltage from said high voltage transformer means to an anode of a cathode-ray tube.

19. A cathode-ray tube display unit according to claim 12, further comprising a transparent conductive coating formed on an external surface of a face plate of said cathode-ray tube and connected to ground and having a resistance value per unit area at 2×

10⁶ Ω

/square! or below.