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Tsutomu OGATA Tohru KOYASHIKI Kenji AKUTO Katsuichi YOTSUMOTO
This paper describes power feed techniques for telephone subscribers in a metallic two-wire digital subscriber loop system and optical fiber subscriber loop systems. In a metallic two-wire digital subscriber loop system, Digital Service Unit (DSU) and Digital Telephone (DTEL) are installed on the subscriber premises. The power consumption of the equipment increases compared with that of the conventional analog telephone. Therefore, it is difficult to feed sufficient power to the equipment using a conventional 48 V constant-voltage power supply. A constant current power feeding method from the central office is suitable because constant power can be obtained with little energy loss. A small-size and low-cost constant current converter has been developed. In optical fiber subscriber loop systems, it is difficult to feed the customer's equipment with power from the central office. Therefore, an uniterruptible DC power unit has to be installed on the subscriber's premises. The power unit is composed of sealed lead-acid batteries and a multi-input converter which has rectifier and DC-DC converter functions. This converter is very small and low-cost. The life of a sealed lead-acid battery can be prolonged by coating the outside of the battery container with aluminum or fluoric-resin film, and by optimizing the calcium content in the electrode grid alloy.