JPH02302176A - Focus circuit for cathode ray tube - Google Patents

Abstract

PURPOSE:To always adjust a focus of a picture to an optimum value by adding a focus voltage adjustment circuit varying a focus voltage in response to the amplitude of a video signal supplied from a video signal output circuit to a cathode electrode of a cathode ray tube. CONSTITUTION:A voltage extracted on the way of a high voltage rectifier circuit of a high voltage generating circuit 3 is divided into a focus voltage required for a display screen of a cathode ray tube 8 with resistors R1, R2 and a variable resistor VR in a focus volume circuit 1, adjusted and fed to a focus electrode 5. In this case, when the amplitude of the video signal supplied from a video signal output circuit 7 to the cathode electrode 6 of the cathode ray tube 8 is subject to change, the impedance of a focus voltage fine adjustment circuit 2 is changed according to the amplitude. Thus, the focus voltage applied to the focus electrode 5 of the cathode ray tube 8 is increased or decreased depending on the amplitude of the video signal fed to the cathode electrode 6, that is, the contrast of the display picture.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a focus circuit for a cathode ray tube, which is applied to a display device that uses a cathode ray tube to display images directly or on a screen.

[Prior Art 1] Fig. 2 is a wiring diagram showing a focus circuit of a conventional cathode ray tube. In the figure, (3) is a high voltage generation circuit, (4
) is the high voltage electrode of the cathode ray tube (8), (5) is the focus electrode of the cathode ray tube (8), (1) is the focus volume circuit, and this focus volume circuit (1) has voltage dividing resistors (R1) and (R2). ) and a variable polyurethane (VR), and the voltage taken out from the middle of the high voltage rectifier circuit (not shown) of the high voltage generation circuit (3) is divided by the variable polyurethane (VR) and applied to the focus electrode. (5)
to be applied.

(8) is the cathode electrode of the cathode ray tube (8), and (7) is a video signal output circuit that outputs the video signal to the cathode electrode (6).
supply to.

Next, the operation of the above configuration will be explained.

The high voltage necessary to drive the cathode ray tube (8) is transferred from the high voltage generation circuit (3) to the high voltage electrode (4) of the cathode ray tube (8).
At the same time, the video signal is supplied to the video signal output circuit (
7) to the cathode electrode (6) of the cathode ray tube (8).

On the other hand, the focus electrode (5) of the cathode ray tube (8) is supplied with the voltage taken out from the middle of the high voltage rectifier circuit of the high voltage generating circuit (3).
1) and (R2), the voltage is divided and applied. At this time, the variable polyurethane (VR) of the focus volume circuit (1)
) to match the image displayed on the cathode ray tube (8) to bring the displayed image into focus.

[Problems to be Solved by the Invention] Since the conventional CRT focusing circuit is configured as described above, when the focus of the image displayed on the CRT is adjusted to match the bright screen, the focus of the dark screen becomes blurred, Also, if you adjust it for a dark screen,
There was a problem with bright screens becoming out of focus.

This invention was made to solve the above-mentioned problems, and it provides a focus circuit for a cathode ray tube that can always optimally adjust the focus of the image displayed on the cathode ray tube, regardless of whether the screen is bright or dark. The purpose is to provide

[Means for Solving the Problems] A focus circuit for a cathode ray tube according to the present invention uses a focus voltage finer that varies a focus voltage applied to a focus electrode of a cathode ray tube in accordance with the amplitude of a video signal supplied to a cathode electrode of the cathode ray tube. It is characterized by the addition of an adjustment circuit.

[Function] According to the present invention, by varying the focus voltage applied to the focus electrode of the cathode ray tube according to the amplitude of the video signal, a focus voltage corresponding to the brightness of the screen is applied to the focus electrode, Regardless of changes in screen brightness, the focus can always be adjusted to the optimum level.

[Embodiment of the Invention] An embodiment of the present invention will be described above based on the drawings.

FIG. 1 is a wiring diagram showing a focus circuit of a cathode ray tube according to an embodiment of this invention 11. In the figure, (1
), (3) to (8) are the same components as the conventional example shown in Fig. 2, so the corresponding parts are given the same reference numerals.
Their detailed explanation will be omitted.

In FIG. 1, (2) is a focus voltage fine adjustment circuit, which is composed of a transistor (Tr) and resistors (R1) and (R2), and is used to control the video signal output from the video signal output circuit (7). The impedance is changed according to the amplitude, and the focus voltage applied to the focus electrode (5) is varied.

Next, the operation of the above configuration will be explained.

The voltage extracted from the middle of the high voltage rectifier circuit of the high voltage generation circuit (3) is applied to the resistance (R) of the focus volume circuit (1).
1), (R2) and variable poly(VR),
The voltage is divided into focus voltages required by the display screen of the cathode ray tube (8), adjusted, and applied to the focus electrode (5).

At this time, the video signal output circuit (7) is connected to the cathode ray tube (8).
) When the amplitude of the video signal supplied to the cathode electrode (8) changes, the impedance of the focus voltage fine adjustment circuit (2) changes in accordance with the amplitude. This results in 2
The focus voltage applied to the focus electrode (5) of the cathode ray tube (8) increases or decreases depending on the amplitude of the video signal applied to the cathode electrode (6), that is, the brightness or darkness of the displayed image.

Therefore, by adjusting the impedance ratio of the focus voltage fine adjustment circuit (2), which changes depending on the amplitude of the video signal, to the characteristic of the brightness of the cathode ray tube (8) versus the focus' city pressure, the brightness of the screen can be affected. Instead, it's always a matter of setting the optimal focus voltage first.

In the above embodiment, the focus voltage fine adjustment circuit (2
) is shown using a transistor (Tr) and resistors (R1) and (R2), but instead of a transistor, an FE
Even if T or the like is used, the same effect as in the above embodiment can be obtained.

[Effects of the Invention] As described above, according to the present invention, the focus voltage applied to the focus electrode is changed to i+f according to the amplitude of the video signal supplied to the cathode electrode of the cathode ray tube. Therefore, the focus of the display image can always be optimized with high accuracy regardless of the brightness of the display image.

[Brief explanation of the drawing]

FIG. 1 is a wiring diagram of a focus circuit for a cathode ray tube according to an embodiment of the present invention, and FIG. 2 is a wiring diagram of a focus circuit for a conventional cathode ray tube. (1)...Focus volume circuit, (2)...Focus voltage fine adjustment circuit, (5)...Focus electrode, (6)...Cathode electrode, (7)...Video signal output circuit. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] (1) In a focus circuit for a cathode ray tube, which includes a focus volume circuit that applies a focus voltage to a focus electrode of the cathode ray tube, and a video signal output circuit that supplies a video signal to a cathode electrode of the cathode ray tube, from the video signal output circuit. A focus circuit for a cathode ray tube, characterized in that a focus voltage fine adjustment circuit is added for varying the focus voltage according to the amplitude of a video signal supplied to a cathode electrode of the cathode ray tube.