| 摘要 |
PROBLEM TO BE SOLVED: To protect a modem from heat generation and burning when the modem is erroneously connected to a telephone line not adaptable to the modem. SOLUTION: The line current limit circuit is provided with a relay inserted in the telephone line to opens/closes the telephone line, a DC loop circuit which is connected to the telephone line and in which the line current of the telephone line flows, an overcurrent detection part generating an overcurrent detection signal when a line current becomes not less than a prescribed value and a latch circuit fixing the relay to an open side when the overcurrent detection signal is supplied from the overcurrent detection part. When the system is connected to the telephone line adaptable to the modem and when an overcurrent flows due to a surge voltage, the overcurrent is speedily interrupted and the modem can be protected. When the overcurrent flows once and the line is interrupted, the relay is fixed to an open side. Thus, the overcurrent is prevented from intermittently flowing and the modem can securely be protected.
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