| 摘要 |
PURPOSE:To make the titled circuit small in size and light in weight by making the voltage at both ends of a capacitor smaller than the reference voltage of a Zener diode for AC signals, making the voltage at both ends of a resistor, for detecting voltage, equal to the voltage of the base of a transistor and ground for DC signals, and making the voltage larger than reference voltage. CONSTITUTION:For AC calling signals of party line telephone, the voltage that appears at both ends of a resistor 6 for detecting voltage is divided by a resistor 7 for AC non-operating and a capacitor 8. When the voltage at both ends of the capacitor 8 is set not to exceed the voltage of a Zener diode 10, the transistor does not operate. On the other hand, as aural signals can be cut off by raising the impedance of a party call detecting circuit, the resistance 6 for detecting voltage is made sufficiently large. In the case where forward DC flows in a diode 5, the voltage of the resistor 6 for detecting voltage is not divided by the resistor 7 for AC non-operating and capacitor 8, and goes to voltage of the capacitor 8 as it is. By setting the voltage to exceed the voltage of the Zener diode 10, the transistor is operated.
|
