CRT driving circuit

Details CRT driving circuit CRT driving circuit

1998-06-25

2001-03-20

Ham, Seungsook (Department: 2878)

Electric lamp and discharge devices: systems

Cathode ray tube circuits

Power supply from deflection circuit source

C315S386000

Reexamination Certificate

active

06204616

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a CRT driving circuit used in a display device using a CRT in a television set or a television set equipped with a video cassette recorder, and more particularly to a CRT driving circuit used to drive the cathode of the CRT.
2. Description of the Related Art
It is well known that with respect to the CRT of a television set or a television set equipped with a video cassette recorder, a monitor screen still illuminates in white spots even after a power switch is turned off. It is said that such a phenomenon, called “remaining spot” or “stray emission”, is attributable to a remaining high voltage because electrons are left in the CRT after the power switch is turned off.
This remaining spot impairs the display as a commodity product. In order to obviate such an inconvenience, conventionally, when the power switch is turned off, a so-called “full white” video signal is been applied to a cathode control circuit of the CRT so that the entire screen illuminates in white, and thereafter a power supply circuit is turned off.
However, such a countermeasure does not discharge the high voltage left in the CRT after the power switch is turned off so that it is only a temporary means for making the remaining spot unattractive, not a substantial solution of the inconvenience. In addition, such a countermeasure places the CRT in an excessively loaded state due to the full white image and hence is not preferred to the CRT.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a CRT driving circuit which can essentially cancel the remaining spot by means of discharging the high voltage of a CRT in a simple circuit configuration when a power switch is turned off.
In order to achieve the above object, the invention provides a CRT driving circuit comprising: a cathode control circuit for amplifying a video signal created by a video circuit and supplying the amplified video signal to a cathode of a CRT; a power supply circuit for creating a power supply voltage for each of the cathode control circuit and the video circuit; a switch circuit for switching on/off the power supply voltage outputted from the power supply circuit to the cathode control circuit; and a monitor control circuit for on/off controlling the switch circuit and the power supply circuit on the basis of a power-on/off signal externally inputted and switching off from on the power supply circuit at a timing later than the switch circuit is switched off when the power-off signal is inputted.


REFERENCES:
patent: 4468715 (1984-08-01), Reno, Jr.
patent: 4985665 (1991-01-01), Sendelweck
patent: 5995385 (1999-11-01), Shimamura
patent: 01149577 (1989-06-01), None
patent: 07231654 (1995-08-01), None
patent: 10341576 (1998-12-01), None

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