| 摘要 |
PURPOSE:To minimize the power consumption at a power failure by providing a line signal detection circuit, a switch closing state self-hold circuit, a line signal detection inhibit circuit and a self-hold release circuit. CONSTITUTION:When a signal on a signal line 101 is detected by a line signal detection circuit 1, a switch closing state self-hold circuit 2 uses the line signal detection circuit 1 to receive the state of the signal detection on the signal line 101 and to close a switch SW thereby holding the closing state. Thus, power supply to an exchange is applied from a power supply 118 through a power input line 117. When a hook switch HS1 is closed, a line signal detection inhibit circuit 3 inhibits line signal detection by the line signal detection circuit 1 in interlocking with the closing of the hook switch HS1. Thus, the power input to an ISDN terminal equipment is controlled at power supply limit such as power failure. |
