| 摘要 |
PURPOSE:To prolong the attach time even when the capacitance of a charge/ discahrge capacitor is small by applying charge/discharge of the AGC voltage at a part of the vertical blanking period. CONSTITUTION:When an AGC error voltage Ve rises and the relation of Ve>Vc is obtained. The collector current of a transistor (TR) Q1 is larger than a con stant current IO corresponding to a difference voltage Vd= ¦Ve-Vc¦ and the collector current of a TR Q4 is larger than the constant current IO. Since the collector current of the TR Q2 is smaller than the constant current IO, the current corresponding to the difference voltage Vd is conducted from the collec tor of the TRQ4 to the capacitor C1, which is charged up. The voltage Vc rises through the charging and when the relation of Ve=Vc is obtained, the charging to the capacitor C1 is stopped. Since the charging is executed only at Pv='L', the terminal voltage Vc of the capacitor C1 rises little by little at every vertical blanking period. Since the AGC is applied by the voltage Vc, the attack time is prolonged.
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