Seasonic Platinum Fanless 520 W Power Supply Review

Secondary Analysis

As one would expect in a high-efficiency power supply, the Seasonic Platinum Fanless 520 W uses a synchronous design, where the Schottky rectifiers are replaced with MOSFETs. Also, the reviewed product 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. Both designs are used to increase efficiency.

The +12 V output uses two BSC018N04LS G MOSFETs, each one supporting up to 100 A at 100° C in continuous mode, or up to 400 A at 25° C in pulse mode, with a maximum RDS(on) of only 1.8 mΩ. These transistors are located on the same printed circuit board as the resonant controller.

Figure 16: One of the +12 V transistors

As explained, the +5 V and +3.3 V outputs are produced by two DC-DC converters, which are situated on the same printed circuit board as the modular cabling system. The converters are controlled by a single APW7159 integrated circuit. Each output uses three RJK0332DPB-01 MOSFETs, each one supporting up to 35 A at 25° C in continuous mode and up to 140 A at 25° C in pulse mode, with a maximum RDS(on) of 3.6 mΩ.

Figure 17: The DC-DC converters

Figure 18: The DC-DC converters

The outputs of the power supply are monitored by a WT7527 integrated circuit, which supports over voltage (OVP), under voltage (UVP), and over current (OCP) protections. This chip offers two +12 V channels, but the manufacturer decided to use only one of them, resulting in this unit having a single +12 V rail. 

Figure 19: Monitoring circuit

The electrolytic capacitors available in the secondary are also Japanese, from Chemi-Con and Rubycon, and labeled at 105° C, as usual. As you can see in Figure 20, several solid capacitors are also used.

Figure 20: Capacitors