PURPOSE: To attain LSI constitution for an imposition filter and an interrupting circuit by slowly turning on and off the flow of current to the base of a feeding transistor (TR) of a public telephone set with a time constant circuit, and by making the constitution to the imposition filter small-sized.
CONSTITUTION: Contacts rl1-1, rl1-2 of an interrupting relay, contacts rl2-1, rl2-2 of a polarity inversion relay, and resistors R3, R3' are connected between a public telephone set 2 and a feeding circuit 2. A series circuit consisting of TR1, TR2 for feeding and resistors R5, R5' is connected between a connecting point between the resistors R3, R3' and the contacts rl1-1, rl1-2, ground and a power supply +48V. Imposition filters 5-1, 5-2 having a time constant circuit consisting of resistors R4, R4', capacitors C, C' and Tr4, Tr4' are provided for the base of the Tr1, Tr2. A current flowing to the Tr1, Tr2 is slowily turned on and off with the time constant circuit and is applied to the telephone set 1 with polarity inversion. In interrupting, photo diodes D1, D1' of interrupting circuits 6-1, 6-2 are turned on with an interruption signal to zero the base current of the Tr1, Tr2.
SAKAI TAKESHI
KIMURA SHIYUUJI
KAMOI NOBUHISA
