| 摘要 |
PURPOSE:To reduce the current supplied from a line and to reduce the number of parts without degrading the insulation resistance of a telephone set by using a D-FF instead of an R/S-FF of an on-hook receiving loudening control circuit. CONSTITUTION:The clock inputs of an FF7 of an on-hook receiving loudening control circuit 3 inverts Q and Q' outputs by switching of a speaker switch 8, and this state is held. The Q output is transmitted to the D input after a certain time by a delay circuit 11. Therefore, the clock is inputted by the second switching of the switch 8 to invert Q and Q' outputs again, and the state is latched. The Q output of the FF7 is connected to the input terminal of a circuitt 4 to be controlled, and the telephone line between the (+) terminal of a diode bridge 2 and a hook switch HS1 is closed or opened by the Q output. Thus, receiving loudening is possible in the on-hook state. Consequently, the circuit has no busses, where the current is always consumed, except the FF7, and a high resistance can be used as a resistance R2, and as the result, the insulation resistance of the telephone set is not degraded. Since the FF7 is used as a latch, an FF for latch is unnecessary. |
