| 摘要 |
PURPOSE:To save power consumption by providing the 1st and 2nd compensating means making a negative feedback voltage nearly equal to a reference voltage when a channel is opened (hook on) so as to avoid ineffective current at hook- on. CONSTITUTION:In case of on-hook, channels B, A are opened and the relation of IB=0 and IA=0 exists. Since a voltage VTHB of an inverting input of an amplifier A4 is smaller than VX, an output level of the amplifier A4 is higher than the earth, a current flows to the forward direction of a diode D1 and a voltage V1' is brought nearly to an earth level. Since a voltage VTHA at a non-inverting input of an amplifier A5 is smaller than VY, a current flows to the forward direction of a diode D2 and a voltage V2' is brought into nearly the same level as a power supply VBB. Thus, the constant current control circuit is made inactivated substantially by bringing the applied voltage V1' of the non-inverting input of the amplifier A1 and the applied voltage V2' at the non-inverting input of the amplifier A2 to the power supply level at on-hook. |
