Importance

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Abstract

In a ringing signal control circuit for controlling supply of a ringing signal from a ringing signal generator to a subscriber's line in response to a call signal destined thereto, a switching element is repeatedly switched to connect the ringing signal generator to the subscriber's line under control of a switching signal from a switch controller. In order to suppress a surge voltage due to connection and disconnection of the subscriber's line for the ringing signal generator, a memory stores a time data signal representative of a transition time from a reference voltage level to an optimum voltage level for the subscriber's line. The optimum voltage level is the level at which the connection and disconnection can be carried out without generation of the surge voltage. A voltage comparator compares the ringing signal with the reference voltage to produce a coincident signal. The switch controller receives the coincident signal and reads the time data signal to produce the switching signal at a time delay of the transition time so that the connection and disconnection of the subscriber's line for the ringing signal generator are carried out at the optimum voltage level of the ringing signal.

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First Claim