JPH01290378A - Spot killer circuit - Google Patents

Abstract

PURPOSE:To reduce a voltage of the 1st grid and the cathode and to prevent damage of a fluorescent screen due to production of a spot by connecting the 2nd grid of an electron gun to ground via a CR circuit and applying an acceleration voltage to the grid via a diode. CONSTITUTION:With a power supply given, the 2nd grid voltage extracted from a flyback transformer 1 is applied to the 2nd grid G2 through a diode D and charges a capacitor C. When power is interrupted, an anode voltage of the diode D is zero and the charge in the capacitor C is preserved. In this case, since the voltage of the let grid G1 and the cathode K is decreased, a cathode current flows and a high voltage charge stored in the capacitor on a cathode ray tube bulb wall is discharged. Then damage on the fluorescent screen due to production of spot is avoided.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is designed to prevent high-voltage charges accumulated in a capacitor formed between the glass bulb walls of a cathode ray tube during image display operation even when the power is cut off. The present invention relates to a spot killer circuit for a cathode ray tube, which, when installed additionally, quickly discharges the charge accumulated in a capacitor after the power is cut off, for a television set that does not disappear immediately.

[Prior Art] Some television receivers use the glass bulb wall of the cathode ray tube as a dielectric material to conduct electricity inside and out during image reception.

High-voltage charges accumulated in capacitors having membranes as electrode plates remain for a while after the power is turned off, causing unsightly phenomena such as so-called spot residue and stray emissions that are harmful to cathode ray tubes.

In order to prevent such a situation, various spot killer circuits have been proposed in the past. They are, for example,
Immediately after turning off the power to the set, the discharge time of the first grid voltage is prolonged, and the first grid voltage is in a state higher than the cathode voltage (positive bias) to force the cathode current to flow, causing the cathode ray tube bulb wall to The main methods used were to discharge the high-voltage charge accumulated in the capacitor, or to erase the spot by increasing the cathode voltage and turning the cathode ray tube into a cut-off state.

[Problems to be Solved by the Invention] However, in the case of conventional spot killer circuits, for example, the method of applying a positive bias to the first grid voltage causes electrons emitted from the cathode to collide with the first grid, and under normal usage conditions, Gas is emitted from the first grid, which is not intended to be hit by electrons and therefore does not generate much gas by electron impact during the exhaust process, and this gas adheres to the cathode, causing electron emission failure. In addition, the method of raising the cathode voltage to achieve the cut-off state is effective because high-voltage charges are accumulated in the capacitor on the wall of the cathode ray tube bulb. This causes electron emission from the adhesion site, so-called stray emission.

SUMMARY OF THE INVENTION An object of the present invention is to provide a spoiler 1-killer circuit that prevents the appearance of residual spots without causing problems such as poor cathode emission and stray emissions as described above.

[Means for Solving the Problems] In order to achieve the above object, in the present invention, the second grid of the electron gun of the cathode ray tube is grounded via a circuit consisting of a capacitor and a resistor, and the forward direction is connected to the second grid. An accelerating voltage was applied through a diode.

[Operation] With the above method, the second grid voltage taken out from the flybank transformer is supplied to the second grid of the cathode ray tube through the diode, but at the same time, the capacitor connected to the second grid is also charged. Ru. When the power to the cell 1- is cut off, the voltage on the anode side of the diode becomes zero, the diode enters a cut-off state, and the charge stored in the capacitor is retained. In this case, since the voltage between the first grid and the cathode decreases, the cathode voltage flows, the high voltage charge stored in the capacitor on the wall of the cathode ray tube bulb is discharged, and no spot is produced.

Embodiment] FIG. 1 shows an embodiment of the present invention. The voltage taken out from the midpoint between the flybank 1 and the lance 1 is supplied to the third grid G3 and the second grid G2 of the cathode ray tube by resistance division. A diode D, a capacitor C5, and a resistor R are connected between the second grid G2 and the second grid voltage output terminal from the flyback transformer l.

When the set is powered on, voltage is supplied from the flyback transformer 1 to each electrode. At this time, the second grid voltage output from the flyback transformer 1 is supplied from the diode D to the second grid G2 and charges the capacitor C. When the power of the set is turned off, the second grid voltage output from the flyback transformer 1 becomes zero, so the voltage charged in the capacitor C causes the diode D to be in a cut-off state, and the second grid voltage becomes the power supply of the set. The value before turning off is held, and it is gradually discharged through the high resistance R. Then, while the second grid voltage gradually discharges and decreases, the voltage between the first grid and the cathode decreases, causing current to flow to the cathode, which discharges the high voltage charge accumulated on the wall of the cathode ray tube bulb and lowers the voltage. Therefore, damage to the fluorescent surface due to spot generation can be avoided.

[Effects of the Invention] As explained above, according to the present invention, when the power to the set is cut off, the voltage applied to the second grid gradually decreases, making the first grid positively biased as in the conventional case. This eliminates the possibility that electrons collide with the first grid and gas is emitted, and the gas does not adhere to the cathode and cause an emission failure.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention. 1... Flyback transformer, D... Diode,
C... Capacitor, R... Resistor, K...
Cathode, G□...1st grid, G2...2nd
grid. G3... 3rd grid. 7γ

Claims (1)

[Claims] 1. A spot characterized in that the second grid of the electron gun of the cathode ray tube is grounded via a circuit consisting of a capacitor and a resistor, and an accelerating voltage is applied to the second grid in the forward direction via a diode. killer circuit.