CABLE MODEM PROVIDED WITH BACKUP FUNCTION AT POWER INTERRUPTION, AND BACKUP METHOD FOR THE MODEM AT POWER INTERRUPTION

摘要

PROBLEM TO BE SOLVED: To make it possible to continue the operation of a cable MODEM while minimizing the power consumption of a backup power supply when an external power supply is interrupted and prevent the cost of a side supplying power via a CATV network from being increased. SOLUTION: When an output DC voltage of an AC adaptor 23 is lower than a prescribed level, a power supply selection circuit 208 selects power from a battery 207. When a microprocessor 203 detects this state, the microprocessor informs a CATV center about it. Then a DC power is superimposed on a coaxial cable 19 being a component of a CATV network 11. A power extract circuit 209 extracts the DC power. When a voltage level of the power extracted by the power extract circuit 209 exceeds a prescribed level, a power supply circuit 206 selects the power from the CATV network 11. Then the power supply selection circuit 208 selects the power from the CATV network 11 selected by the power supply circuit 206.