JPS6346877A - Focusing adjustment circuit - Google Patents

Abstract

PURPOSE:To improve the characteristic by superposing a a parabolic wave voltage to a certain focus voltage to correct the focus voltage at the time of horizontally scanning the peripheral part and the center part of the screen of a CRT. CONSTITUTION:The pulse voltage taken out from a focus improving winding 5C is allowed to pass an integrating inductance 12 and a capacitor 13 to obtain the parabolic wave voltage synchronized with a horizontal synchronizing signal, and this voltage is applied to a focus electrode 9B. With respect to an optimum focus voltage applied to the electrode 9B, the parabolic wave voltage is superposed to the certain voltage due to a variable resistor 8. Thus, the optimum focus voltage corresponding to the horizontal scanning position of a bright point on the screen of a CRT 1 is obtained, and the best focus characteristic is obtained throughout the screen of the CRT 1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a focus adjustment circuit for adjusting focus in a cathode ray tube (hereinafter referred to as CRT).

[Conventional technology]

FIG. 3 is a diagram showing a focus adjustment circuit described, for example, in Color Television Receiving Techniques 9 edited by Japan Broadcasting Corporation (published February 1986), page 142. In the same figure, 1
is a horizontal output transistor, 2 is a damper diode, 3 is a horizontal output transistor,
is a resonant capacitor, 4 is a power supply, and 5 is a fly bank transformer (hereinafter referred to as FBT). 5A is the primary winding of the FBT5 to which the horizontal output transistor 1 and the power supply 4 are connected to each end, 5B is the high voltage secondary winding of the FBT 5 whose one end is grounded, and 6 is the high voltage secondary winding from the high voltage secondary winding 5B. A diode 7 rectifies the high voltage signal, and a capacitor 7 charges the rectified high voltage signal.

8 is a variable resistor for focus adjustment whose stator side is connected in parallel to capacitor 7, 9 is a CRT, 9A is an anode electrode of CRT 9 connected to capacitor 7, and 9B is connected to the rotor side of variable resistor 8. This is the focus electrode of the CRT9.

Next, the operation will be explained. When a drive voltage synchronized with the horizontal synchronizing signal is applied to the base of the horizontal output transistor 1, due to the time constant due to the inductance of the FBT 5, resonance with the resonant capacitor 3, and the action of the damper diode 2, the negative winding 5A of the FBT 5 has the following: A sawtooth wave current flows. As a result, the high voltage secondary winding 5B of the FBT5 has
A high voltage pulse voltage is generated that is proportional to the amount of current change per unit time and the turns ratio. This high voltage pulse voltage is rectified by a diode 6 and charged to a capacitor 7. A focus voltage obtained from a variable resistor 8 that divides the voltage of the capacitor 7 is applied to a focus electrode 9B to adjust the focus of the CRT 9.

[Problem that the invention seeks to solve]

Since the conventional focus adjustment circuit is configured as described above, the focus voltage is a constant value, and the difference in focal length between the center and periphery of the CRT display screen (the optimum focus voltage is different between the center and the periphery) ) cannot be corrected, and when the focus is set on the center (of the CRT display screen), the peripheral areas become out of focus.

This invention has been made to solve the above problems, and aims to provide a focus adjustment circuit that can vary the focus voltage in each scanning period of the peripheral and central areas of the display screen during flat scanning. purpose.

[Means for solving problems]

The focus adjustment circuit according to the present invention provides a focus improvement winding on the secondary side of the FBT, integrates the voltage generated in the focus improvement winding using an integral superposition circuit, and superimposes the voltage generated in the focus improvement winding on a constant focus voltage. It is designed to be supplied to the focusing electrode of.

[Effect]

The focus adjustment circuit according to the present invention superimposes a parabolic wave voltage synchronized with a horizontal synchronizing signal on a constant focus voltage using an integral superimposition circuit and supplies the superimposed voltage to a focusing electrode of a CRT, thereby controlling the peripheral and central portions of a CRT screen. The focus voltage is corrected during horizontal scanning to improve focus characteristics.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, parts with the same symbols as those in FIG. 3 are the same as those in the conventional example, and their explanation will be omitted. 10 is FBT, 5
C is FBTIO primary winding 5A and high voltage secondary winding 5B
In addition, there is a focus improvement winding, 1, which is specially provided on the secondary side of the FBTIO for focus improvement and has one end grounded.
1 is a current limiting resistor, 12 is an integral inductance, 1
3 is an integrating capacitor, and 14 is a coupling capacitor.

The current limiting resistor 11, the integrating inductance 12, and the coupling capacitor 4 are connected in series in this order between the other end of the focus improving winding 5C and the focusing electrode 9B. Further, the integrating capacitor 13 is connected between the connection point between the integrating inductance 12 and the coupling capacitor 14 and the ground.

FIG. 2 shows voltage waveforms at various parts in FIG. 1.

The pulse voltage V1 taken out from the focus improvement winding 5C is supplied to the integrating inductance 12 and the integrating capacitor 13 through the current limiting resistor 11, and is integrated. At this time, if the impedance constants of the integrating inductance 12 and the integrating capacitor 13 are selected to appropriate values, there will be a horizontal open IJI between both ends of the integrating capacitor 13.
A parabolic wave voltage ■2 synchronized with the satellite is generated. This voltage V2 is passed through the coupling capacitor 14 to the focus electrode 9.
This is in addition to B. Therefore, the optimum focus voltage (3) applied to the focus electrode 9B is obtained by superimposing the parabolic wave voltage (2) on the constant voltage divided by the variable resistor 8, as shown in FIG.

The optimal focus voltage for the CRT 9 requires a higher voltage toward the periphery, depending on the shape of the image display surface of the CRTl. Therefore, when the focus voltage is constant as in the past, there is a problem that the peripheral area shifts when focusing on the center, but as mentioned above, it is possible to superimpose the parabolic wave voltage (2) on the constant focus voltage. By C
The optimum focus voltage (3) corresponding to the horizontal scanning position of the bright spot on the screen of the RTI can be obtained, and the best focus characteristic can be obtained over the entire screen of the CRT1.

In the above embodiment, a focus improvement winding of a flyback transformer, an integrating inductance, and a capacitor are provided in order to obtain a parabolic wave voltage, but it is also possible to obtain a parabolic wave voltage with other circuit configurations. good.

〔Effect of the invention〕

As described above, according to the present invention, the FBT is provided with a winding for focus improvement, the voltage generated in this winding is integrated, and the integrated value is superimposed on a constant voltage to generate a periodic wave-like focus voltage. Since the structure is configured to generate , there is an effect that optimum focus can be obtained at the center and periphery of the CRT screen.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of a focus adjustment circuit according to an embodiment of the present invention, FIG. 2 is a waveform diagram showing voltage waveforms of each part in FIG. 1, and FIG. 3 is a conventional focus adjustment circuit. It is a circuit diagram. In the figure, 5B is a secondary winding for high voltage, 5C is a focus improvement winding, 6 is a diode, 7 is a capacitor, 8 is a variable resistor, 9 is a CRT, 9B is a focus electrode, 10
is an FBT, 11 is an integrating resistor, 12 is an integrating inductance, 13 is an integrating capacitor, and 14 is a coupling capacitor. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. 4′

Claims (1)

[Claims] In a focus adjustment circuit that divides the high voltage obtained by rectifying the high voltage pulse generated in the high voltage secondary winding of the flyback transformer and supplies it to the focus electrode of the cathode ray tube, the focus adjustment circuit is provided on the secondary side of the flyback transformer. What is claimed is: 1. A focus adjustment circuit comprising: a focus improvement winding that has been adjusted, and an integrating/superimposing circuit that integrates a voltage generated in the focus improvement winding and superimposes the integrated value on the divided voltage.