Development of an Efficient, Lightweight Switched-Mode Power Supply for Telecommunications Network Use

This paper discusses the development of an efficient, lightweight switched-mode power supply (SMPS) for reducing cost and energy consumption and for simplifying essential maintenance procedures at small telephone offices. This SMPS consists of a voltage regulator, control circuits, protection circuits and five rectifier units including one redundant unit. Each rectifier unit weighs only 9 kg and can be handled by one person during maintenance. These features are realized through the employment of a single-ended forward-type 20-kHz conversion circuit. Furthermore, an effective decrease in rectifier unit weight and power loss is accomplished by designing the input filter to suppress high-frequency voltage ripple only, while designing for low-frequency voltage ripple to be absorbed in the conversion circuits. The efficiency of each rectifier unit is maximized by developing and using a new high-speed, high-voltage transistor for the conversion circuit and by improving the winding methods used in fabricating the transformer and the inductor, as well as by a loss reduction technique for the input filter. Accordingly, this SMPS can convert 200-volt, three-phase AC power to 48-volt DC with better than 90% efficiency, and it can supply output power up to 5 kW.