When to and why use fixed-ratio bricks

摘要

With systems of fixed size, availability of ac source voltages, and no need for backup power, a 12-V output ac/dc front end can be used to directly provide the intermediate bus voltage and the isolation from the ac line input. This scheme is most efficient as it avoids additional power conversion stages (see Fig. 1). In very large (over-1,500-W) scalable telecom systems that use battery backup, the common system distribution voltage among all the circuit boards is nominally -48 Vdc. Then an isolated dc/dc stage is required to convert the -48 Vdc to a +12-Vdc intermediate-bus voltage on each circuit board.