JPS6228118Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cathode spot killer circuit, and more particularly to a spot killer circuit for preventing burn-in of phosphor on the display screen of a cathode ray tube.

A phosphor layer is provided on the display surface of the cathode ray tube.
An electron beam is irradiated onto this phosphor from an electron gun, and information is displayed by the fluorescence emitted from the electron beam. First, a large amount of charge temporarily remains on the anode due to the internal capacity of the cathode ray tube.

For this reason, even after the power supply to the cathode ray tube is stopped, the electrons emitted from the cathode are still accelerated and irradiated onto the phosphor layer. However, as mentioned above, since the deflection system has stopped operating, the electrons from the cathode The light is not deflected and is irradiated only to a specific portion of the phosphor layer provided on the display surface. As is well known, when a phosphor is irradiated with an accelerated electron beam in a concentrated manner, its light emitting characteristics rapidly deteriorate and display quality deteriorates. Conventionally, for this reason, during the transient period when the power supply voltage supply to the cathode ray tube is stopped, the bias of the cathode ray tube is made shallow, a large amount of beam current is passed, the charge remaining on the anode is neutralized, and the anode voltage is lowered. This prevents acceleration of electrons emitted from the cathode, lowers the irradiation energy to the phosphor layer, and prevents deterioration of the phosphor. However, with this method, if the power supply voltage to the cathode ray tube is stopped while the cathode is not sufficiently heated, the amount of beam emitted from the cathode is small and the neutralization development described above is insufficient, causing the charge on the anode to decrease. A large amount remains, and the electron beam from the cathode is accelerated and deteriorates the phosphor on the display screen. The present invention was developed in view of the above, and aims to provide a cathode ray tube spot killer circuit that detects the stoppage of power supply voltage to the cathode ray tube and blocks the cathode current. The present invention is characterized by comprising means for detecting the voltage level supplied to the heater of the electron gun, and a control circuit for adjusting the voltage supplied to the grid of the cathode ray tube based on the output level of the detection circuit means. Preferred embodiments of the present invention will be described in detail below with reference to the drawings.
FIG. 1 is a circuit configuration diagram of one embodiment of the present invention.
is an AC power supply, 2 is a flyback transformer, 3 is
A first rectifier circuit forms a first power supply unit that supplies output to a heater of a cathode ray tube (not shown).
It has a diode 3a and a smoothing capacitor 3b. K is an output level detection means of the power supply 3. 4
5 is a transistor for detecting power cut-off, and 5 is a Zener diode connected to the emitter of the detection transistor 4 to maintain the emitter voltage of the transistor 4 at a constant value. 6 is a base resistor, and the collector of the transistor 4 is connected to the base of the switching transistor 8 via the resistor 7. The emitter of the transistor 8 is connected to a DC power supply P (second power supply section), and the collector is connected to one terminal of a variable resistor 9. C is a control circuit. A terminal 9a of the variable resistor 9 is connected to a grid of a cathode ray tube (not shown). The other end of variable resistor 9 is connected to the output side of second rectifier circuit 10 . Second rectifier circuit 1
0 is rectifier diode 10a, smoothing capacitor 1
0b, and the input side is a flyback transformer 2.
is connected to the secondary coil of Next, the operation of this circuit will be explained. When the switch 1a is turned from open to closed and the supply of power from the AC power source 1 to the transformer 2 is started, rectification is performed in the first and second rectifier circuits 3 and 10, and the output terminal (diode capacitor The output at the connection point ) becomes a voltage at a constant level and is applied to the heater of the electron gun of the cathode ray tube (not shown), and is also applied to the base of the detection transistor 4 via the resistor 6. The output level of the first rectifier circuit 3 is the Zener voltage V _z , the sum of the base-emitter forward direction V _T1 of the transistor 4 V _z
The diode 3a and capacitor 3b are selected so that the voltage is larger than +V _T1 , and since the transistor 4 is turned on after the power supply 1 is turned on, the collector voltage of the detection transistor 4 decreases, and the base voltage of the switching transistor 8 decreases. This transistor 8 turns on and its collector voltage becomes the power supply P.
It becomes approximately equal to the output voltage of V _p . On the other hand, the voltage at the output end of the second rectifier circuit 10 (the connection point between the diode 10a and the capacitor 10b) is a constant value _V2 . Therefore, the voltage applied between both terminals of the variable resistor 9 is V _p -V ₂ , and the voltage appearing at the output terminal 9a has a variable value determined by the division ratio between the two terminals. Therefore, the voltage appearing at this output terminal 9a is applied to the grid of the cathode ray tube (not shown).
It becomes possible to adjust the display brightness of the cathode ray tube. Next, when the switch 1a is opened and the power supply from the AC power source 1 is stopped, the voltages V _P and V ₂ applied to both terminals of the variable resistor 9 and the output voltage of the first rectifier circuit 3 V ₁
gradually decreases, and when the output voltage of the first rectifier circuit 3 becomes V _z +V _T1 or less, the detection transistor 4 turns off, and accordingly, the switching transistor 8 also turns off, so that the switching of the variable resistor 9 The terminal voltage on the transistor 8 side decreases and becomes equal to the terminal voltage on the second rectifier circuit 10 side. Since charge is accumulated by the capacitor 10b included in the second rectifier circuit 10, the output level of the rectifier circuit 10 gradually decreases, and the voltage applied to the grid of the cathode ray tube (not shown) also increases. The output voltage level is 10, and the electron beam emitted from the electron gun of the cathode ray tube is blocked by the grid and does not reach the phosphor on the display screen. In this case, after the power supply from power supply 1 is stopped, the power supply stop is immediately detected and the grid voltage of the cathode ray tube is lowered, so the electron beam from the electron gun is blocked by the grid and the phosphor on the display screen is This has the advantage that no irradiation occurs, preventing burning of the phosphor and extending the life of the cathode ray tube.

[Brief explanation of the drawing]

The figure is a circuit configuration diagram of an embodiment of the present invention. 1: AC power supply, 2: flyback transformer,
3: first power supply section, 4: transistor, 5: Zener diode, 6, 7: resistor, 8: transistor, 9: variable resistor, 10: third power supply section, P : second power supply section.

Claims (1)

[Scope of utility model registration request] A means for detecting the supply voltage level to the heater of the electron gun of the cathode ray tube, and is provided between the DC power source and one terminal of the resistive element, and is connected or disconnected depending on the output of the detection means. It is provided with a control circuit having a switch means, a constant voltage power source connected to the other terminal of the resistor element, and is configured to supply the voltage obtained from the resistor element to the grid of the cathode ray tube, and When the voltage supplied to the heater of the gun becomes less than a predetermined value, the switching means is turned off, and the second constant voltage power supply voltage is supplied to the grid, thereby shielding the electron beam from the electron gun. A spot killer circuit for a cathode ray tube.