JPH0354460Y2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Field of Industrial Application The present invention relates to a dynamic focus circuit used in a display device using a picture tube such as a television receiver or a CRT display.

(b) Prior Art In order to obtain the same optimal focus state at the periphery of the picture tube screen as in the center, a dynamic camera is designed to vary the focus voltage of the picture tube between the center and the periphery. The cass circuit is generally constructed as shown in FIG. 4, as shown in, for example, Japanese Utility Model Publication No. 56-18050. That is, 1 is a horizontal deflection/high voltage generation circuit including a horizontal output transistor _Q1 , a horizontal deflection coil Ly, etc., and the primary winding of a flyback transformer (FT) in this circuit.
The pulse generated at _N1 is rectified and smoothed by diode _D1 and capacitor _C1 , and a DC voltage is extracted. This DC voltage is supplied as a power source to the control transistor Q ₂ via the resistor R ₁ , and a bias voltage is applied to the base of the control transistor Q 2 by the voltage dividing resistors R ₃ and R ₄ . The parabolic wave voltages A and B are applied through level adjustment variable resistors VR ₁ and VR ₂ and coupling capacitors C ₂ and C ₃ , respectively.

On the other hand, the DC high voltage obtained from the secondary high voltage winding N ₂ of the flyback transformer FT via the high voltage rectifying diode D ₂ is applied to the anode electrode A of the picture tube 2.
and the DC high voltage voltage dividing circuit 3
A focus DC voltage is taken out from one of the variable resistors _VR3 through a resistor _R5 . and,
A composite parabolic wave voltage C as a dynamic focus modulation voltage obtained from the collector of the control transistor _Q2 is combined with this DC voltage via a DC blocking capacitor _C4 , and the voltage after the combination is applied to the picture tube 2. The voltage is applied to the focus electrode _G3 . In addition, the voltage dividing circuit 3
The DC voltage taken out from the other variable resistor VR ₄ is applied to the screen electrode G ₂ of the picture tube 2.

(c) Problems that the invention aims to solve By the way, as is well known, the focus voltage that provides the optimal focus state has a relationship of a certain ratio K (about 30%, although it varies depending on the picture tube) to the anode voltage. It is in. Therefore, in general, by dividing the high voltage for the anode electrode to obtain the focus voltage, the focus voltage can be made to follow changes in the anode voltage depending on the brightness of the screen, etc., and the above ratio relationship can be maintained. I am trying to do what is called focus tracking.

However, when a dynamic focus circuit is added, as in the conventional example shown in Figure 2, the focus voltage accurately follows changes in the anode voltage due to the DC blocking capacitor _C4 in this circuit. The problem is that it doesn't. That is, in FIG. 4, for example, if the anode high voltage at point P rises, the potential at point Q also tends to rise by the above-mentioned constant ratio K in response. However, due to this potential increase, the capacitor is
Since _C4 is charged, the voltage at point Q will not reach the above value until this charging is completed. Conversely, when the high voltage for the anode drops, the potential at point Q similarly does not drop to the predetermined value until the discharge of the capacitor _C4 , which is carried out along the path indicated by the dashed line, is completed. .
Therefore, if the beam current of the picture tube 2 flows only in the upper half of the screen, as shown in FIGS. 5a and 5b, for example,
The anode voltage changes as shown in c in the figure, and the DC potential at point Q (d in the figure) should change as shown in the broken line, but it only changes as shown in the solid line. Since the voltage C is superimposed, there is a drawback that focus slacking cannot be performed accurately.

SUMMARY OF THE INVENTION The present invention has been devised in view of the above, and an object of the present invention is to enable accurate focus tracking in a dynamic focus circuit.

(d) Means for solving the problem In this invention, the first capacitor for DC blocking is added to the focus DC voltage obtained by dividing the dynamic focus modulation voltage of the picture tube by dividing the high voltage for the anode electrode. In this circuit, a second capacitor was connected between the connection point between the first capacitor and the focus electrode and the anode electrode.

(E) Effect According to the above configuration, the first and second capacitors act as a capacitance dividing circuit for the high voltage for the anode electrode, whereby high voltage fluctuations are immediately transmitted to the focus electrode, and the focus voltage is accurately adjusted to the anode. Follow the voltage.

(F) Embodiment FIG. 1 shows an embodiment of the dynamic focus circuit of the present invention. In this example, the fourth
Parts that are the same as those in the figures are given the same numbers and explanations are omitted; however, the following features are featured. A second capacitor _C5 is connected between the connection point Q of the first DC blocking capacitor _C4 for superimposing the modulated voltage and the focus electrode _G3 and the anode electrode A.
The first and second capacitors C ₄ and C ₅ constitute a capacitance dividing circuit for the anode voltage at point P.

Here, since the DC potential at point Q is determined by the voltage dividing circuit 3 as in the prior art example, the voltage dividing ratio is set to the constant ratio K. Next, the AC potential at point Q is the potential of the first and second capacitors relative to the potential at point P.
Although determined by the capacitance ratio of C ₄ and C ₅ and the potential at point R, the potential at point R is about several hundred volts, whereas the voltage between QR is about several kilovolts. Therefore,
Ignoring the potential at point R above, the first and second capacitors
The capacity ratio of C ₄ and C ₅ (C ₄ +C ₅ )/C ₄ is set to the above ratio K. At this time, this capacitance ratio does not necessarily need to be set accurately to the ratio K, and some variation can be tolerated, the reason for which will be explained later.

According to this configuration, when the high voltage for the anode at point P fluctuates as described above, the fluctuation is immediately transferred to the focus electrode of the picture tube 2 via the second capacitor _C5 .
Applied to _G3 . Moreover, since the voltage fluctuation applied to the electrode _G3 is adjusted to satisfy the above-mentioned ratio K by capacitance division of the first and second capacitors _C4 and _C5 , the focus voltage is adjusted to the above-mentioned anode. This allows accurate tracking of voltage fluctuations. That is, if Fig. 3a is the dynamic focus voltage at point Q when the anode voltage is constant, then when the anode voltage changes as shown in Fig. 5c, the focus voltage changes as shown in Fig. 3b. This is the translation.

Note that when the voltage at point P is constant, the potential at point Q is equal to the potential at point Q' in the voltage divider circuit 3.
At this time, even if there are variations in the capacitance values of the first and second capacitors C ₄ and C ₅ , the amount of charging and discharging of each capacitor is automatically adjusted so as to satisfy the above relationship. This means that variations in this are not a problem.

Further, FIG. 2 shows another embodiment of the present invention, and this embodiment has an anode voltage extraction circuit 4.
is configured as a multi-voltage rectifier type, and the DC voltage for focusing is obtained from the front stage side, but since it is basically the same as the embodiment shown in Fig. 1, the corresponding parts are The same drawing numbers will be used and the explanation will be omitted.

(g) Effects of the invention According to the dynamic focus circuit of the invention, it is possible to change the focus voltage so that the optimum focus state is achieved even in the peripheral area of the screen, and the focus voltage can be changed by changing the anode voltage. Since the image can be accurately followed, the best image quality can always be obtained regardless of changes in screen brightness.

[Brief explanation of the drawing]

Figures 1 to 3 relate to the present invention; Figure 1 is a circuit diagram showing one embodiment, Figure 2 is a circuit diagram showing main parts of another embodiment, and Figure 3 is a focus voltage waveform. It is a diagram. FIG. 4 is a circuit diagram showing a conventional dynamic focus circuit, and FIG. 5 is a diagram for explaining its drawbacks. 3... Voltage divider circuit, G ₃ ... Focus electrode, C ₄
...First capacitor, C ₅ ...Second capacitor.

Claims (1)

[Scope of utility model registration request] The high voltage for the anode electrode of the picture tube is divided by resistance, and the DC voltage obtained by this voltage division is applied to the first voltage for DC blocking.
In a circuit that synthesizes dynamic focus modulation voltages via a capacitor and applies the synthesized voltage to a focus electrode of a picture tube, a connection point between the first capacitor and the focus electrode and an anode electrode are provided. A dynamic focus circuit characterized in that a second capacitor is connected between the first and second capacitors, and the variation of the high voltage is applied to the focus electrode by the first and second capacitors.