Not Just About POLs
When looking at the Intermediate Bus Architecture (IBA), there is a tendency to focus on point-of-load (POL) dc-dc converters and the various control and monitoring schemes while skipping over the upstream bus converter that steps down the front end's 48 V to the bus-distribution voltage. In fact, a great deal can be said about bus converters. Not all bricks are created equal.
Input Voltage Range's Big Impact
Apart from physical dimensions, brick converters differ the most in their input voltage ranges. IBA designers who have to meet legacy telco specifications must select wide-input (36- to 75-V) bus converters, even though the outputs of modern ac-dc front ends will never see swings that wide. Engineers designing for IT applications or for the communications infrastructure in developing countries can select narrow input-range converters with more efficiency and higher power densities than their wide-range cousins. A narrow input range gives the brick designer freedom to leave the output unregulated. If the input range doesn't vary much, variations in output will be small, because the transformer turns ratio constrains them.