| 摘要 |
PURPOSE:To simplify circuit constitution, to reduce its cost and to enhance a spot killer effect by connecting a means, which interrupts supply of brightness adjusting voltage when it becomes a certain voltage, to the side supplying the brightness adjusting voltage to a variable resistor in terms of a display having a brightness adjusting circuit. CONSTITUTION:A transistor R in a spot killer circuit is normally energized, and the spot killer circuit supplies a voltage Vg (-40V) which is obtained by dividing voltages Vk (+60V) and Vd (-100V) by a variable resistor RV to the 1st grid G1 of a CRT1. When power supply is turned off under this condition, the voltage Vk (+60V) is falling. When the voltage is lowered below Zener voltage (30V) point (b), the transistor T is brought into the interrupted condition. Due to this interruption a supply voltage Vg to the 1st grid G1 is directly applied to a discharge voltage of -100V of a condenser C1, and a potential difference Vkg between a cathode K voltage Vk and the 1st grid G1 voltage Vg becomes larger; therefore emission of electronic beams is cut off and a spot will not remain.
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