| 摘要 |
PROBLEM TO BE SOLVED: To make speech quality stable and to realize low cost and low current consumption by using a feeding circuit for the communication equipment as a constant current supply circuit, so as to make a subscriber current constant, thereby preventing a change in a speech current even when a DC resistance component of a station side is subject to change. SOLUTION: A transformer 20 is used to couple a trunk line system and a speech circuit 30 of a key telephone set 1. A DC voltage component is cut off by separately providing a trunk line system and the speech circuit 30 by means of the transformer. A constant current circuit 40 is provided to supply a current to a trunk line 90, while making the flowing current constant. The constant current circuit 40 and a power supply section 50 are provided to make a speech current to always flow constantly, even when a DC resistance at the trunk line side fluctuates. Thus, the speech quality is kept stable, and it is not required to use a power supply with a large capacity even with respect to fluctuation in a resistor of the trunk line, so as to reduce the capacity of the power supply thereby making a master set of the key telephone system small. |
