JP2000036914A - Spot killer circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a spot killer operation stable by using a leading of a nega tive voltage so as to forcibly bring a G2 voltage to zero volt when power is turned off. SOLUTION: A negative power supply E1 is generated at application of power and a capacitor C1 is charged through a charging diode D1. A base voltage of a spot killer output transistor(TR) Q1 reaches 0 V and the TR Q1 is in a cut-off state. When power is turned off, the negative power supply E1 rises and a base current is supplied to the base of the spot killer output TR Q1 through the capacitor C1 by charges stored in the capacitor C1, the spot killer output TR Q1 becomes conductive and a G2 voltage is discharged to ground through a current limit resistor R1. The capacitor C1 is required to have a capacity of storing charges by which a base current of the spot killer output TR Q1 is continuously supplied till the discharge of the G2 voltage is finished.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus in which a spot killer circuit such as a television or a display monitor using a cathode ray tube is provided on a G2 electrode.

[0002]

2. Description of the Related Art In televisions and display monitors using CRTs, deflection circuits and high voltage circuits are stopped when the power is turned off, but the capacity of the CRTs (about 1500 pF).
And the high-voltage capacitor in the flyback transformer (about 300
(0 to 6000 pF), the high voltage remains without being discharged, so that the electron beam continues to fly, and as a result, a spot is generated near the center of the tube surface, causing burning.

Conventionally, in order to prevent this, a method of controlling the G1 and the cathode electrode, which are the beam control electrodes of the cathode ray tube, in a direction in which the beam current decreases to reduce the spot is mainly used.

In the conventional method described above, since the cut-off variation of the cathode ray tube is adjusted by the voltage between the G1 and the cathode, there is a disadvantage that the voltage which operates as a spot killer varies and a spot is generated. there were.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a spot killer circuit which eliminates the above-mentioned disadvantages of the prior art and prevents burnout of a CRT due to spots even when the cutoff of the CRT varies. .

[0006]

According to the present invention, a spot killer circuit is provided at a G2 voltage terminal.

[0007] The spot killer circuit of the present invention has a negative voltage E
By detecting the rise of 1 and setting the G2 voltage to 0 V, burning of the CRT is prevented.

[0008]

FIG. 1 shows an embodiment of a spot killer circuit according to the present invention (when a transistor is used as a switching element).

When the set is turned on, a negative power supply E1 is generated, and the capacitor C1 is charged through the charging diode D1. At this time, the base voltage of the spot killer output transistor Q1 is 0 V, and is in a cutoff state.

When the set is turned off, the negative power supply E1 rises, and the electric charge stored in the capacitor C1 causes the capacitor C1 to be connected to the base of the spot killer output transistor Q1.
Base current flows from 1. As a result, the spot killer output transistor Q1 is turned on, and the voltage G2 is discharged to the ground through the current limiting resistor R1. At this time, the capacitor C
1 must have a capacity capable of accumulating a charge capable of continuing to flow the base current of the spot killer output transistor Q1 until the discharge of the G2 voltage is completed.
When the set is turned on again, a negative voltage E1 is generated, and the spot killer output transistor Q1 is turned off.

FIG. 2 is a characteristic diagram showing a change in voltage when the set is turned on and off.

From FIG. 2, according to the present invention, the spot killer output transistor Q1 is turned off when the set is turned on, and the spot killer output transistor Q1 is turned off when the set is turned off.
Indicates that the G2 voltage is lowered.

[0013]

According to the present invention, the conventional G1
-Unlike a spot killer circuit that increases the potential difference between cathodes, G1-
Since the G2 voltage is discharged to 0 V irrespective of the voltage between the cathodes, a stable spot killer operation is performed, and burning of the cathode ray tube due to spots can be prevented.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of a spot killer circuit of the present invention (when a transistor is used as a switching element).

FIG. 2 is a characteristic diagram showing a change in voltage when a set is turned on and off.

[Explanation of symbols]

V1: CRT, T1: Flyback transformer, E1: Negative power supply, Q1: Spot killer output transistor, D1: Die auto for charging capacitor, C1: Capacitor, R1: Spot killer output transistor Current limiting resistor, R2: Spot killer output transistor on Time setting discharge resistor.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Shoji Shimizu 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture F-term in Hitachi Image Information System Co., Ltd. 5C058 AA01 BA35 CA07 CA11 5C068 FA02 GA13 MA05

Claims (1)

[Claims] 1. A spot killer circuit for a television, a display monitor, or the like using a cathode ray tube, wherein the G2 voltage is forcibly set to 0 V when the power is turned off by using the rising of a negative voltage.