| 摘要 |
PCT No. PCT/GB95/00382 Sec. 371 Date Aug. 22, 1996 Sec. 102(e) Date Aug. 22, 1996 PCT Filed Feb. 24, 1995 PCT Pub. No. WO95/23455 PCT Pub. Date Aug. 31, 1995A switching device for a telecommunications channel. The device comprises a voltage detector, a switch, and a storage device. The voltage detector produces an output voltage if the voltage between the lines of the channel exceeds a predetermined level, for example 110 volts. The switch can increase an impedance in one of the lines (preferably causing open circuit) in response to an input voltage. The first storage device, for example a capacitor, produces the input voltage when it reaches a charge V2; is initially at a voltage V1, for example zero, that is less than V2; after charging by the output voltage from the voltage detector, is at a voltage V3 greater than V2; and discharges from V3 to V1 in the absence of the output voltage. The voltage detector comprising a low-pass filter such that an AC signal on the channel produces an output voltage that charges the first storage device to a charge below V2. |
