| 摘要 |
PURPOSE:To provide a telephone line power utilization circuit where the duty factor of the first order side switching element of a DC-DC converter is controlled and receiving efficiency is improved. CONSTITUTION:In a telephone line power utilization circuit 1 utilizing DC power to be supplied from the side of a telephone line as the power source of a line terminal equipment main body circuit TA by a DC-DC converter CN, a CPU 2 with AD converter controls the duty factor of the first order side switching element Tr1 so that the DC resistance RS of the line terminal equipment viewed from the side of the telephone line may be within the range satisfying a prescribed specification and the input DC resistance of the DC-DC converter CN may be a maximum. Thus, DC power to be supplied from the side of the telephone line can be utilized to the maximum as the power source of the line terminal equipment. |
