| 摘要 |
Subscriber circuits for a domestic telephone system do not need to perform all the tasks defined by the so-called BORSCHT functions. The AC ringing current, DC feed current and audible tones are often supplied asymmetrically, and detection and evaluation means are provided in the subscriber circuit to identify loop closure. To reduce circuit cost, a voltage regulator with a pulsed load resistor is provided in the subscriber circuit to supply the DC feed current and audible tones and to identify loop closure, and the AC ringing current is supplied by means of a TRIAC. The loop signal is fed to a control device and a ringing disablement device and evaluated in the control device for ringing disablement. Automatic ringing disablement when the handset is taken off-hook in the subscriber device is achieved by combining the loop signal and the ringing enablement signal in the ringing disablement device.
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