Technologies and Future Trends in Rectifiers for Customer Premises Telecommunications Equipment

Rectifiers for Bell System customer premises telecommunications equipment such as Private Automatic Branch Exchanges (PABX or PBX), key telephone systems (KTS), and data sets employ a variety of technologies. That variety includes linear transformers, ferroresonant transformers, and, in a few instances, line rectifiers followed by dc-dc converters. For multiple output rectifiers, these technologies are combined with linear regulators and/or switching regulators to control most or all outputs. In the United States, a 60-Hz ferroresonant transformer is frequently used to eliminate problems caused by lightning strikes on the ac feeders, or surges caused by load changes or source switching on these feeders. Lightning strikes and voltage surges can be mitigated by other means, however, thus allowing designers to apply many of the techniques used in dc-dc converters operating above 20 kHz, to rectifiers connected to ac sources of 50 or 60 Hz. This paper discusses circuit topologies for such high frequency power supplies as well as methods for overcurrent limiting, inrush current limiting, overvoltage protection, and mechanical packages to meet unusual thermal and mechanical constraints.