Electric lamp and discharge devices: systems – Cathode ray tube circuits – Power supply from deflection circuit source
Reexamination Certificate
1999-02-25
2001-10-30
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Power supply from deflection circuit source
C315S382100
Reexamination Certificate
active
06310448
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a CRT display device to be used in a projector apparatus etc. and is particularly suitable in reducing discharge current that flows through a CRT (cathode-ray tube) when an abnormal discharge has occurred there.
2. Description of the Related Art
In various television receivers and monitor apparatuses of the CRT type, because of the structure of the electron gun used in the CRT, an abnormal discharge may occur between the anode and the cathode (electron gun) owing to foreign matter such as dust that exists inside the CRT.
Conventionally, to prevent an abnormal discharge in the CRT, various improvements and developments have been made in the electrode shapes of the electron gun, the method for polishing the electrode surfaces, the shape of the electrode supporting glass rods, the knocking characteristic, the inside coating (employment of a coating having high peel strength), etc.
In addition to the above improvements and developments, various studies and developments have been made of the method for reducing the discharge current of an abnormal discharge to prevent the CRT itself or peripheral circuits from being damaged even if an abnormal discharge occurs inside the CRT.
An example method for reducing the discharge current when an abnormal discharge occurs inside the CRT is employment of a PCE (peak current equalizer) in which a stainless lead wire for supplying a prescribed voltage to an electrode of the electron gun is replaced by a ceramic resistor of several kilo-ohms so that the cathode-side discharge path has a relatively high impedance.
However, even if the cathode side of the CRT is given a relatively high impedance, there still remains a possibility that the cathode or the heater of the electron gun that is provided on the cathode side or a circuit part connected thereto is damaged when a relatively large discharge current flows into the cathode side.
There are other possibilities that an abnormal sound is generated inside the CRT and that the peripheral circuits operate erroneously to impair its own functions of the television receiver or the monitor apparatus.
In particular, a projector apparatus or the like in which CRTs of red (R), green (G), and blue (B) are used, when an abnormal discharge has occurred in one of the R, G, and B-CRTs, say, the R-CRT, a discharge current coming from a high-voltage capacitor that is provided in a high-voltage block for supplying an anode voltage and discharge currents caused by the coating capacitances of the other CRTs where no abnormal discharge has occurred flow into the R-CRT in an additive manner. As a result, a relatively large discharge current flows into the cathode side (electron gun) of the R-CRT where the discharge has occurred, which causes a trouble in the cathode or the heater of the electron gun or a circuit part connected thereto, for example, it is damaged.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a CRT display device which is free of any trouble even if an abnormal discharge occurs in a CRT.
The invention provides a CRT display device comprising high-voltage generating means for generating high-voltage pulses; high-voltage distributing means for converting the high-voltage pulses to a high voltage having a prescribed voltage value and distributing the high voltage; a CRT supplied with the high voltage at an anode thereof; and a discharge current limiting resistor provided in a high-voltage supply line for supplying the high voltage from the high-voltage distributing means to the anode of the CRT.
The discharge current limiting resistor may have a sufficiently larger resistance value than an inside carbon coating that is formed in the CRT.
The high-voltage distributing means may be one that distributes the high voltage to three CRTs that generate three primary color pictures, respectively.
According to the invention, by providing the discharge current limiting resistors having, for example, a sufficiently larger resistance than the inside carbon coatings in the high-voltage supply lines for distributing a high voltage produced by the high-voltage distributing means to the anodes of the respective CRTs, a discharge current coming from the high-voltage capacitor to a CRT where an abnormal discharge has occurred can be reduced and discharge currents coming from the coating capacitances of the remaining CRTs can be inhibited.
The invention is particularly effective when applied to a projector apparatus using three CRTs, because discharge currents flowing from the coating capacitances of CRTS where no abnormal discharge has occurred to a CRT where an abnormal discharge has occurred can be prevented almost completely.
REFERENCES:
patent: 3855614 (1974-12-01), Okada
patent: 3898381 (1975-08-01), Amsen et al.
patent: 4045742 (1977-08-01), Meehan et al.
patent: 4404500 (1983-09-01), Stow
patent: 4599642 (1986-07-01), Willis
patent: 4679092 (1987-07-01), Blanken et al.
patent: 4703345 (1987-10-01), Matsuzaki et al.
patent: 5589883 (1996-12-01), Ogino et al.
Kawamura Yuusuke
Kikuchi Hiroaki
Oosuga Satoshi
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Sony Corporation
Tran Thuy Vinh
Wong Don
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