| 摘要 |
PURPOSE:To approximate the limitation starting value of a beam current to a doming generation value as much as possible and to expand a luminance range by interposing an amplifier which amplifies potential variation between the 1st and the 2nd resistances. CONSTITUTION:When the voltage at a point VC drops below about 30V, an operational amplifier 3 lowers in output level to drops the emitter potential of a transistor (TR) 4, lowering the voltage to the 1st grid G1. Consequently, the beam current (i) decreases and consequently when the voltage at the point VC rises, the output level of the amplifier 3 rises to rise the voltage to the 1st grid G1. In this case, when the gain of the amplifier 3 is high, the voltage to the 1st grid G1 is varied greatly in response to slight potential variation at the point VC. Therefore, if the current (i) almost exceeds the limitation starting value, i.e. if the voltage at the point VC almost drops below about 30V, the potential returns to about 30V smoothly by high-gain negative feedback even when the limitation starting value of the current (i) is approximated to the doming generation value. Consequently, the occurrence of doming is prevented. |
