Patent ID: 7822195

Claim:
A telephone interface circuit comprising: a first transistor for controlling opening and closing between a speech circuit and subscriber lines; a second transistor for controlling the first transistor to turn on and off; a positive feedback circuit connecting a collector terminal of the first transistor and a base terminal of the second transistor; a terminal connecting the base terminal of the second transistor and a microcomputer; an overcurrent detection circuit detecting overcurrent applied to the subscriber lines; and a breaker circuit for turning off the first transistor by lowering the base potential of the second transistor to a low potential when the overcurrent is detected at the overcurrent detection circuit, wherein the base terminal of the first transistor and a collector terminal of the second transistor are connected, and when off-hook, the base potential of the second transistor is controlled in such a manner as to become a high potential by the microcomputer via the terminal.