| 摘要 |
A power switch device is used with a telephony instrument that is connected to a local phone loop via two telephone wires and that has two power lines for connection to a power source. The device includes a rectifier connected to the telephone wires, and a latching relay having an exciting coil connected to the rectifier via a differentiator, and a switch unit. The coil is excited by current flowing through the differentiator when a ring signal is present at the telephone wires so as to enable the switch unit to make connection between the power lines and the power source. An integrator is connected between the rectifier and the coil, and discharges when neither the ring signal nor a talking signal is present at the telephone wires so as to excite the coil and enable the switch unit to break connection between the power lines and the power source.
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