JPS60210081A - Focus voltage controller - Google Patents

Abstract

PURPOSE:To obtain pictures of high contrasts by supplying the focus voltage of an optimum level to a focus voltage controller when it is used when a general broadcast screen is received and also used as a terminal display device of a computer, etc. CONSTITUTION:When a general broadcast screen is received, the focus voltage is controlled by a variable resistor VR3. Then the base voltage of a transistor TRTr1 which is applied in a reception mode of general broadcast screen is eliminated when a signal is supplied to a picture receiver from a computer. Thus the TRTr1 is turned off. Therefore a variable resistor VR4 is inserted in series to the resistor VR3. Then a CRT current raises up the focus voltage at a point C by a prescribed degree by means of the VR4. Thus the focus level is set at a point approximate to its best level. This secures pictures of high contrasts.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION This invention relates to a focus voltage adjustment device applied to a cathode ray tube of a television receiver or the like.

Conventional configuration and its problems A conventional focus voltage adjustment device is shown in FIG.

In the figure, T1 is a flyback transformer, and D I
+D2 is a diode for rectifying the flybank pulse and applying it to the anode electrode of the picture tube and the focus voltage adjustment circuit, respectively. R1 is diode D2
This is a fixed resistor for adjusting the focus voltage rectified by. VR.

is a variable resistor for adjusting the voltage to the best voltage based on the focus voltage characteristics of the picture tube, and one side is grounded.

FIG. 2 shows the relationship between cathode ray tube current and focus voltage. In the figure, ■ indicates the characteristics of the picture tube. In other words, this characteristic indicates the optimum focus voltage for the cathode ray tube current.

■ and ■ are the focus voltages actually applied to the cathode ray tube, and ■ is the focus voltage and cathode ray when the focus voltage is adjusted with the variable resistor VR, shown in Figure 1, in region A where a large amount of cathode ray tube current flows. This shows the relationship between tube current. 3 shows the characteristics when adjusted in region B where the cathode ray tube current is small.

Here, if the focus voltage generated from the flybank transformer T1 matches the focus characteristics of the cathode ray tube, the focus will be optimal no matter what the cathode ray tube current is.

However, it is difficult to perfectly match the focus characteristics of the cathode ray tube and the flybank, and when the focus voltage is adjusted at point A, as shown in A difference of ΔV1 occurs between the focus characteristic (2) and the focus characteristic (2). Furthermore, when adjusting at point B as shown in ■ in Figure 2, a difference of Δ■2 generally occurs between the focus characteristic ■ of the cathode ray tube and the focus characteristic ■ of the cathode ray tube at point A, where a large amount of cathode ray tube current flows. be. These differences ΔVl+Δ■
2 is out of focus and appears on the screen, and its value is about 100 to 200 cm.

These do not pose much of a problem when receiving general broadcasts, etc., but when displaying characters etc. mainly on a computer etc., there is a problem in that a clear image cannot be obtained.

Purpose of the Invention The purpose of the present invention is to supply a focus voltage to the focus electrode of a cathode ray tube that is optimal for both when receiving general broadcasting and when used as a terminal display device for computers etc. (mainly when displaying characters). It is an object of the present invention to provide a focus voltage adjustment device.

Structure of the Invention The focus voltage adjustment device of the present invention includes a focus voltage output terminal, a first variable resistor connected to the output terminal, and a second variable resistor connected in series to the first variable resistor. The switching element is connected in parallel to the second variable resistor and is turned on when the second variable resistor is not in use, and is cut off when the second variable resistor is in use.

The switching element shorts the second variable resistor by applying a voltage so as to be turned on when receiving general broadcasting, and the focus voltage applied to the cathode ray tube is adjusted only by the first variable resistor. do. In addition, when the receiver is used as a terminal display device for a computer or the like, the switching element is turned off and the focus voltage at that time is set in advance by a first variable resistor and a first variable resistor connected in series. Set by adjusting the variable resistor in step 2.

That is, it is possible to independently supply the best focus voltage depending on the received signal (general broadcast or computer terminal display signal).

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 3 and 4. In the figure, T2 is a fly bank transformer, and the fly hack pulse generated by this transformer is rectified by a diode D3 and applied to the anode of the picture tube. Further, the voltage rectified by the diode D4 is adjusted by the first fixed resistor R3 and the variable resistor VR3, and is applied to the focus electrode of the picture tube.

Now, when receiving a general broadcast screen, the transistor T
A voltage ■ is applied to the head of r1.

Therefore, the first variable resistor VR3 is connected to the transistor Tr1.
The focus voltage at this time is adjusted by the first variable resistor VR3.

FIG. 4 shows the relationship between the focus voltage and the cathode ray tube current, and ■ indicates the focus characteristic of the picture tube.

The first variable resistor V is connected to the region where a large amount of cathode ray tube current flows.
2 shows the relationship between the focus voltage and the cathode ray tube current when the focus voltage is adjusted by R3. As can be seen from this, at point B where the cathode ray tube current is small, the voltage actually applied is lower by Δ■4 relative to the focus characteristic (■) of the picture tube. Therefore, this causes out-of-focus, but it does not pose much of a problem when receiving general broadcasts.

However, when used as a terminal display device for a computer, if characters or the like are mainly displayed, the out-of-focus becomes noticeable and a clear image cannot be obtained.

In this embodiment, when a signal from the computer is input to the receiver, the base voltage of the transistor Tr1, which was applied when receiving general broadcasting, disappears, and the transistor T
Set r1 to be off. Therefore, the second variable resistor VR4 is inserted in series with the first variable resistor VR3. This second variable resistor VR4 adjusts the cathode ray tube current so that it increases by Δ■3 at the zero point.

In other words, the second variable resistor VR raises the focus voltage by Δ■3 compared to ■ in all cathode ray tube current regions. ■ indicates this characteristic.

As you can see, B-0 has particularly low cathode ray tube current.
It can be seen that the focus voltage at the point has been improved to approach the best point by Δv3.

In reality, when a computer signal is input, the maximum value of the cathode ray tube current is suppressed to point D by adjusting the brightness control voltage so that the cathode ray tube current is reduced. By the way, this is done to prevent blurring from occurring.

As mentioned above, when receiving a general broadcast, the focus voltage is adjusted by the first variable resistor ■R3, and when the signal from the computer is input, the focus voltage is adjusted by the first variable resistor VR3, which has already been adjusted. A focus voltage adjusted by the second variable resistor VR4 connected in series and according to the input signal can be applied to the focus electrode of the picture tube, improving the focus level.

Effects of the Invention According to the present invention, by making a very simple structural improvement such as adding a second variable resistor, defocus can be suppressed not only when receiving general broadcasting but also when used as a terminal display device for computers and the like. This has the effect of producing a clear image.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a conventional focus voltage adjustment device, Figure 2 is a circuit diagram of a conventional focus voltage adjustment device.
Figure 3 is a characteristic diagram showing the relationship between the cathode ray tube current and focus voltage, Figure 3 is a circuit diagram of a focus voltage adjustment device according to an embodiment of the present invention, and Figure 4 is the relationship between the focus voltage and cathode ray tube current. FIG. VH2...First variable resistor, VH4...Second variable resistor, 1゛r1...Transistor (switching element) Fig. 1 - r&Whole tube current (μA) Fig. 2

Claims (1)

[Claims] (11) A focus voltage output terminal, a first variable resistor connected to this output terminal, a second variable resistor connected in series to this first variable resistor, A focus voltage adjustment device comprising a switching element connected in parallel to a second variable resistor and conductive when the second variable resistor is not in use and cut off when the second variable resistor is in use. (2) The output terminal is The focus voltage adjustment device according to claim 11, wherein the focus voltage adjustment device is connected to the cathode of a diode whose anode is connected to the secondary winding of a flybank transformer.