DC Power Requirements for the Digital Central Office Switch

This paper investigates the DC power requirements for the various domestically manufactured digital central office switches. The subject of DC voltage control is investigated and described for those switches needing close DC voltage regulation. The DC power requirements, once defined, may then be satisfied using various technologies. The rectifier is the main element in the DC power system and the technologies utilized (controlled ferroresonant, thyristor, switched mode rectifier) are discussed. The advantages and disadvantages of each technology as applied to powering the digital central office switch are discussed. The DC power requirements for Digital Control Office Switchers are considerably different from the power demands of previous electromechanical central office switching equipment. With the high degree of technological sophistication inherent in modern digital switchers, one may assume a similar degree of sophistication is required for the DC power plant; but in actuality, the power plant for a digital switch is much simpler than may be expected. Switching systems such as crossbar and step-by-step require very close voltage control, typically -45 volts -50 volts, for proper relay operation. Load current drains are high and vary widely with traffic. A typical 18,000 line crossbar office may be powered by a 2000 ampere -48 volt, 2 step emergency cell power plant, (23 cell +2 cell +2 cell). Depending upon the manufacture, the same number of lines served by a digital switch may only require one third to one half the load current drain.