| 摘要 |
PURPOSE:To prevent a telephone call tone from ringing together by inputting an output of a terminal 2 of a telephone tone transmission circuit to a voltage detection circuit and using a voltage of the terminal 2 to turn on/off a switching circuit. CONSTITUTION:Let a voltage of a capacitor C2 when an incoming tone is given to L1, L2 be E1, and the relation of E1, E2, E3 is set to be E1>E3>E2, so that the switching circuit is turned on when an input to a voltage detection circuit 2 is E3 or over and the circuit is turned off when the input is less than the E3. When a telephone call comes, a square wave is outputted from the terminal 2. The operation that a voltage E1 is applied to a ringer 4 when the square wave output is E1 and no voltage is fed to the ringer when O is repeated and a call tone is generated from the ringer 4. In case of a dial pulse, since the relation of E2<E3 exists in the output from the terminal 4, a voltage detection circuit 2 remains off and the square wave output from the terminal 2 is not fed to the ringer 4. Thus, in case of the dial pulse, no call tone is generate from the ringer 4.
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