Using redundant DC power in high availability systems

Telephone central offices have used redundant -48 Vdc power for many years. Recently, the increasing adoption of the Advanced Telecommunications Computing Architecture (ATCA), which requires equipment operate from redundant -48 Vdc power, has renewed interest in this powering scheme. This paper reviews the three main ways to combine redundant -48 Vdc power to create isolated power rails for the system´s circuits: diode ORing, independent dc-dc converters and multiple input dc-dc converters. Each method is compared and contrasted to the others with regards to cost, complexity and fault tolerance. Example implementations of each are shown. The paper then looks at making the diode ORing input method, popular because of its relative low cost, fault tolerant. The conclusion is that there is no one best way for all systems. Instead each system designer must understand their application and the tradeoffs among the three methods.