| 摘要 |
PROBLEM TO BE SOLVED: To compose a protecting circuit of a little circuits and to provide the inexpensive circuit having a self-recovery function surely showing a protecting state by serially connecting a protection resistance circuit to a subscriber's line, short-circuiting a protecting resistor and controlling the ON/OFF of a switch by detecting an abnormal current flowing in the subscriber's line. SOLUTION: Feeding resistors 2a and 2b are connected to terminals T and R respectively. Protecting resistors 3a and 3b are connected to the other terminals of the feeding resistors 2a and 2b. An electronic feeding circuit 1 is connected to the other terminals of the protecting resistors 3a and 3b. The electronic feeding circuit 1 is composed of electronic coils 9a and 9b having the same equivalent inductance as that of a coil and an electronic switch 5 for polarity inversion. Both the terminals of the protecting resistors 3a and 3b are short-circuited by a switch 4 of two contacts respectively. The electronic switch 5 is connected to the power source part of the electronic feeding circuit 1 and by switching the electronic switch 5, the DC voltages of the terminals T and R are inverted.
|
