Spot eliminating circuit of an image display device

Details Spot eliminating circuit of an image display device Spot eliminating circuit of an image display device

1997-12-30

2000-04-04

Westin, Edward P.

Electric lamp and discharge devices: systems

Cathode ray tube circuits

Cathode-ray deflections circuits

315381, 315384, 348173, H01J 2952, G09G 104

Patent

active

060465522

ABSTRACT:
A spot is prevented from occurring on the center portion of a cathode ray tube when electric power is turned off by using a voltage charged in a capacitor which are used for outputting a vertical blanking signal in a vertical blanking signal generating circuit of an image display device for displaying an image in use of the cathode ray tube. The present invention is provided with a discharge cut-off element between a negative electric power source and the capacitor for outputting a vertical blanking signal and a discharging element for discharging a charged voltage of the capacitor to the ground. The present invention prevents a charged voltage ofthe capacitor from being discharged until thermoelectrons are not emitted from the cathode so as to supply a negative charged voltage to the first grid of the cathode ray tube continuously, so that a spot is prevented from occurring. All the negative voltage charged in the capacitor is discharged when a time period has elapsed during which occurrence of a spot is blocked.

REFERENCES:
patent: 4340910 (1982-07-01), Valdes
patent: 4814880 (1989-03-01), Kugimura
patent: 5043639 (1991-08-01), Gurley et al.
patent: 5084657 (1992-01-01), Ueda
patent: 5677730 (1997-10-01), Park

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