Relayless switching circuit for application of ringing signals

In combination with a telephone, a signal transmitting circuit having an interface transformer, a winding forming a part of said transformer, and a ringing generator which is responsive to a pre-selected signal to produce an a.c. voltage, a switching circuit having first and second semiconductor means, said first semiconductor means being in series with said winding in a first circuit branch, said second semiconductor means being in series with said generator in a second circuit branch, and said first and second circuit branches being connected in parallel across operating terminals of said telephone, said second semiconductor means being effective to couple d.c. ringing voltage pulses to said operating terminals only on the occurrence of half cycles of only one pre-selected polarity of said a.c. voltage, and said first semiconductor means being effective upon the occurrence of said d.c. pulses to effectively open the circuit which connects said first branch across said operating terminals.

A telephone transmission system comprising signal transmission means, a telephone instrument, a transformer normally coupling said telephone instrument to said transmission means and having first and second winding means, said first winding means being connected to said transmission means, a ringing generator energizable from an inactive state to an active voltage-producing state by a pre-selected ring control signal, and circuit means for connecting said generator to said telephone to couple pulses of ringing voltage to said telephone, said circuit means including a semiconductor device which is normally conductive when said generator is in said inactive state to complete a signal transmitting circuit between second winding means and said telephone, the bias of said semiconductor device being controlled by voltage conditions which are developed when said generator is in its active voltage-producing state to effectively open said signal transmitting circuit during the occurrence of said pulses.

In combination with a telephone, a telephone transmission line adapted to be connected to a central office, a talking circuit normally electrically connected to said telephone to provide a signal-transmitting connection between said telephone and said transmission line, and a normally de-activated ringing generator located at the talking circuit end of said transmission line remote from said central office, said generator being turned on to develop an a.c. output voltage in response to the occurrence of a pre-selected signal which signals an incoming call to said telephone, the improvement comprising a static switching circuit connected to said generator, said talking circuit and said telephone for maintaining said generator effectively electrically disconnected from said telephone in absence of said output voltage, and said switching circuit being rendered effective by said output voltage (a) to convert said output voltage into a pulsating d.c. ringing voltage and to apply said pulsating ringing voltage to said telephone to operate the telephone's ringer and (b) to effectively electrically disconnect a portion of said talking circuit from said telephone during application of the pulses of ringing voltage to said telephone.

In combination with a telephone, a telephone transmission line adapted to be connected to a central office, a talking circuit normally electrically connected to said telephone to provide a signal-transmitting connection between said telephone and said transmission line, and a normally de-activated ringing generator located at the talking circuit end of said transmission line remote from said central office, said generator being turned on to develop an a.c. output voltage in response to the occurrence of a pre-selected signal which signals an incoming call to said telephone, the improvement comprising a static switching circuit connected to said generator, said talking circuit and said telephone for maintaining said generator effectively electrically disconnected from said talking circuit in absence of said output voltage, and said switching circuit being rendered effective by said output voltage to apply a pulsating d.c. ringing voltage to said telephone to operate the telephone's ringer.