| 摘要 |
PURPOSE:To prevent one telephone set in busy from being troubled by the interruption of other telephone set by making it impossible for other telephone set to close and to connect a line when the plural telephone sets are connected to the same telephone line, and when one telephone set has closed and has connected the line. CONSTITUTION:When other telephone set 10 does not close and does not connect the telephone line, if a hook switch 9 is closed, a voltage, supplied to a voltage regulator diode 6 through a diode bridge 3 and a dial circuit 4, comes larger than a break down, and therefore a trigger current flows in the gate of a thyristor 8. Accordingly, because the thyristor 8 comes conductive and holds itself, a current flows in a speaking circuit 5, and the telephone line can be closed and connected. When the telephone set 10 colses and connects the telephone line first of all, if the hook switch 9 is closed, because the voltage, supplied to the diods 6, does not exceed the break down voltage, the trigger current does not flow in the thyristor 8, and the thyristor 8 does not come conductive and the current does not flow in the speaking circuit. Accordingly, this telephone set circuit operates so as not to close and not to connect the telephone line.
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