JPS6119587Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a focus circuit for a cathode ray tube such as a television receiver.

It is generally known that focus deviations occur in cathode ray tubes depending on the magnitude of the beam current.

In the focus circuit of ordinary television receivers, there is no relationship between the focus adjuster and the brightness adjuster; the brightness adjuster is set to a certain state at the factory, and the focus is adjusted to the optimum value under that condition. Every time the user adjusted the brightness adjuster, a focus shift occurred. Therefore, there have been some models in which the focus adjuster can be adjusted from outside the set as a user volume, but it is extremely troublesome and inconvenient to adjust the focus each time.

In particular, in the case of a cathode ray tube used as a viewfinder for a video camera, it is necessary to adjust the focus of the television camera depending on the image, and a shift in focus can be fatal. Furthermore, television cameras can be used in a wide range of conditions, ranging from use in dark surroundings to use in direct sunlight, resulting in considerable differences in the beam current of the cathode ray tube. For this reason, it is extremely difficult to keep the focus of the cathode ray tube fixed.

The present invention has been devised in view of these points, and it is an object of the present invention to provide a focus circuit for a cathode ray tube that, once adjusted at the factory, does not require focus adjustment even if the brightness is adjusted thereafter.

The present invention will be explained below according to embodiments shown in the drawings. Figure 1 shows a circuit configuration diagram of one embodiment of the present invention. Here, the DC voltage obtained from the secondary coil side of the flyback transformer FBT via the diode D ₁ is applied to the resistors R ₁ and R ₂ and for focus adjustment. CRT via resistor R ₃ from slider of variable resistor VR ₁
The DC voltage is applied to the focus electrode of the CRT, and here the DC voltage is divided by resistors R ₄ and R ₅ and a brightness adjustment variable resistor VR ₂ , and the focus is applied from the slider of the variable resistor VR ₂ via resistor R ₆ . In addition to being applied to the electrodes, the voltage is further divided by resistors R ₇ and R ₈ and applied to the cathode electrode of the cathode ray tube CRT via resistor R ₉ . Note that the video signal here is a cathode ray tube CRT.
is supplied to the first grid.

In the circuit configured as above, the focus of the image on the cathode ray tube CRT can be adjusted by varying the focus adjustment variable resistor VR ₁ , and the cathode bias of the cathode ray tube can be adjusted by varying the brightness adjustment variable resistor VR ₂ . can be changed to adjust the brightness, but when adjusting the brightness, the focus voltage is also changed at the same time, so the focus is adjusted at the same time.

Here, when the brightness adjustment variable resistor VR ₂ is changed and the brightness control voltage Va applied to the cathode of the cathode ray tube CRT is changed, the focus control voltage Vb applied to the focus electrode becomes linear as shown in Figure 2. By setting the constants of each of the resistors R ₁ to _{R 6} in advance so as to exhibit suitable change characteristics, it is possible to always maintain the best focus state even when brightness is adjusted.

According to the focus circuit of the present invention, even when the brightness is adjusted as described above, the focus state is always maintained in a good condition, and there is no need to perform focus adjustment. Therefore, it is possible to image visual fields of various brightness with a television camera. This is also advantageous when the brightness is frequently adjusted, making it extremely suitable as a focus circuit for cathode ray tubes used in viewfinders of television cameras.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of one embodiment of the present invention;
The figure is a characteristic diagram of the brightness-focus control voltage of the same embodiment. CRT...Cathode ray tube, VR ₁ ...Variable resistor for focus adjustment, VR ₂ ...Variable resistor for brightness adjustment.

Claims (1)

[Scope of utility model registration request] A focus for a cathode ray tube, characterized in that a brightness control voltage variably adjusted by a variable resistor for brightness adjustment is superimposed on a focus control voltage variably adjusted by a variable resistor for focus adjustment and applied to a focus electrode of the cathode ray tube. circuit.