Rosewill CAPSTONE-550M Power Supply Review

Secondary Analysis

The Rosewill CAPSTONE-550M uses a DC-DC design in its secondary. This means that the power supply is basically a +12 V unit, with the +5 V and +3.3 V outputs produced by two smaller power supplies connected to the main +12 V rail. Also, the +12 V output uses a synchronous design where the rectifiers were replaced with MOSFETs. Both designs are used to increase efficiency.

The +12 V output uses four IPP041N04N G MOSFETs, each one supporting up to 80 A at 100° C in continuous mode or up to 400 A at 25° C in pulse mode, with a maximum RDS(on) of 4.1 mΩ.

Figure 13: Two of the four +12 V transistors

As explained, the +5 V and +3.3 V outputs are produced by two DC-DC converters. Both are located on the same daughterboard that is soldered to the main printed circuit board. Each converter is controlled by an NCP1587A integrated circuit and uses two ME70N03S MOSFETs. Each transistor supports up to 62 A at 25° C or 50 A at 70° C in continuous mode or up to 100 A at 25° C in pulse mode, with a maximum RDS(on) of 11 mΩ. 

Figure 14: The DC-DC converter

Figure 15: The DC-DC converter

The outputs of this power supply are monitored by the resonant controller, which doubles as the monitoring circuit.

The electrolytic capacitors that filter the outputs are also Japanese, from Chemi-Con, and labeled at 105° C, as usual.