| 摘要 |
PURPOSE:To improve the contrast on a picture and the fidelity of color luminnescence by comparing a mean video modulation level to a picture-tube current within the range in which an automatic picture-tube current limiting circuit is not in operation and by controlling the level of the picture-tube current to a width that comes up to the standard. CONSTITUTION:Video amplifying integrated circuit 2 is provided connecting with video detecting circuit 1 that limits the anode current of picture tube 7 automatically and further, resistance 21 is connected between terminal 10 of the video amplifying circuit and the connection point between capacitor 14 and flyback transformer 9 connected to the anode of picture tube 7 generate a voltage across at both ends of resistance 21 in proportion to the current of the picture tube. This voltage is applied via amplifying circuit 22 to input terminal 24 of comparing circuit 23, the other terminal of which is applied with a voltage proportional to a mean video modulation level from input part 25. Then, circuit 23 compares the modulation level to the picture-tube current to apply a signal, controlling the picture-tube current, to external bias terminal 14 through driving circuit 26 and within the range in which circuit 2 is not in operation, the level of the picture-tube current is limited to a width that comes up to the standard. |
