| 摘要 |
PURPOSE:To close an aperture without exception after the disconnection of a power supply, by additionally providing a capacitor charged from a power supply voltage when current is flowed and a circuit to close the aperture through the amount of charge of the capacitor at the interruption of power supply. CONSTITUTION:In a monitor TV camera, a capacitor 6 is charged with a power supply voltage from a terminal A during the usage. If the power supply is interrupted, it is detected with a circuit 7 which generates an aperture stop signal by using a photocoupler or the like, and a signal closing the aperture the same as high luminance through the charge in a cpacitor 6 is applied to a level adjusting circuit 2. Simultaneously, a backup voltage corresponding to the power supply voltage from a terminal B is applied to a level adjusting circuit 2 to keep each circuit at an operation state and the aperture wings of an aperture switching circuit 4 are rapidly driven toward the closing direction the same as at high luminance. Thus, the aperture can automatically be stopped through the interruption of the power supply in any state, allowing to minimize the deterioration of a pickup tube. |
