| 摘要 |
PURPOSE:To preclude a screen from becoming abnormal and an overcurrent protection circuit from malfunctioning by detecting a beam current at the time of the in-tube discharge of a cathode-ray tube, applying a negative pulse to the electrode of the cathode-ray tube G1, and cutting off the cathode-ray tube. CONSTITUTION:When the cathode-ray tube causes in-tube discharge and the screen becomes abnormally bright, the beam current increases extremely. This beam current is detected by a transistor (TR) 2 to generate the negative pulse, which is applied to the electrode G1 of the cathode-ray tube. The cathode-ray tube, therefore, becomes large in the difference between the cathode voltage and G1 voltage in the period of the negative pulse and is cut off, so that the screen becomes dark. Conseqently, the screen never becomes abnormally bright and the beam current does not flow excessively, thereby preventing the overcurrent protection circuit from malfunctioning. |
