| 摘要 |
PURPOSE:To eliminate a state wherein a capacitor is charged to such a voltage that a lockout is caused and to prevent the lockout by providing a comparing circuit which outputs a comparison signal when the held voltage of the capacitor exceeds a specific value, and supplying charging or discharging current to the capacitor. CONSTITUTION:The comparator 15 of the comparing circuit 14 compares the held voltage VH of the capacitor C with a reference voltage Vr and a Schmitt circuit 16 supplies a charging or discharging current to the capacitor C when the comparison output of the comparator 15 shows a potential difference greater than a constant value. Therefore, when the held voltage VH is high enough for AGC operation, e.g. between VH1 and VH2, the comparing circuit 14 outputs no signal and normal AGC operation is carried out. When VH<VH1-VH2, the charging current I1 flows to the capacitor C by the output of the comparing circuit 14 and the held voltage VH approximates a normal value to prevent the lockout. When VH>VH1-VH2, the discharge current I2 flows out of the capacitor C by the comparing circuit 14 to hold the held voltage VH1 between VH1 and VH2, preventing the lockout. |
