H - Electricity – 04 – M
Patent
H - Electricity
04
M
379/12
H04M 3/02 (2006.01)
Patent
CA 1293072
ABSTRACT OF THE DISCLOSURE The present invention relates to an apparatus for sending a ringing signal to a called subscriber. Connection and disconnection of the signal takes place with the aid of the apparatus. The problem solved by the invention is that of current transients being generated on disconnection of the signal, these transients causing a disturbing clicking noise in the engaged telephone of a subscriber in a neighbouring channel. The apparatus solving the problem includes a two-way switching circuit connected in series with an AC voltage generator, said circuit disconnecting the AC voltage to a bell when the current through the bell has its zero crossing, and a discharge circuit for discharging the bell before it is connected via a relay to a SLIC circuit, such that the voltage across the bell is within the SLIC circuit voltage interval when the relay connects the bell to the SLIC circuit, which occurs when said signal is disconnected. With this arrangement an overvoltage protector connected to the SLIC circuit is not triggered, and the circuit is not subjected to any current transient which can cause disturbing clicking noises.
579127
Marks & Clerk
Telefonaktiebolaget Lm Ericsson
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