Light spot suppression circuit for a cathode ray tube

Details Light spot suppression circuit for a cathode ray tube Light spot suppression circuit for a cathode ray tube

1975-12-17

1977-11-01

Wilbur, Maynard R.

Electric lamp and discharge devices: systems

Cathode ray tube circuits

Cathode-ray deflections circuits

315384, 315386, H01J 2952

Patent

active

040567583

ABSTRACT:
An improved circuit for suppressing the occurrence of a sharply-focused light spot on the screen of a television receiver when the set is turned off is described. A normally conductive, controllable electronic switch is normally effective to maintain the brightness control grid of the cathode ray tube blocked, such switch assuming its non-conductive state only during the presence of the normal forward sweep portion of the deflection voltage to impart a positive step in voltage to the control grid to permit the now-moving light spot to be visible on the screen. During the flyback portion of the deflection voltage, or equivalently during the disabling of the TV set so that no forward sweep voltage is present, the controllable switch reverts to its "fail-safe" conductive condition to immediately restore the negative blocking voltage on the control grid to inhibit the beam current and thereby the formation of the now-stationary light spot.

REFERENCES:
patent: 3185886 (1965-05-01), Leitich et al.
patent: 3426240 (1969-02-01), Lester
patent: 3775637 (1973-11-01), Brady

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