Seasonic G-550 Power Supply Review

Secondary Analysis

As one would expect in a high-efficiency power supply, the Seasonic G-550 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 PSMN2R6-40YS MOSFETs, each one supporting up to 100 A at 100° C in continuous mode, or up to 651 A at 25° C in pulse mode, with a maximum RDS(on) of 5.3 mΩ. These transistors are located on the solder side of the printed circuit board, using the power supply case as their heatsink.  

Figure 16: 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 a single printed circuit board located in the secondary section of the power supply. The converters are controlled by an APW7159 integrated circuit and use seven IPD060N03L G MOSFETs: four of them are used by the +5 V output and three of them are used by the +3.3 V output. Each transistor supports up to 50 A at 100° C in continuous mode and up to 350 A at 25° C in pulse mode, with a maximum RDS(on) of 6 mΩ.

Figure 17: The DC-DC converters

Figure 18: The DC-DC converters

The outputs of the power supply are monitored by a PS223 integrated circuit, which supports over voltage (OVP), under voltage (UVP), over current (OCP), and over temperature (OTP) protections. There are four OCP channels available, but the manufacturer decided to use only one of them, making the reviewed unit use a single +12 V rail configuration.

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. A few solid capacitors are also used.

Figure 20: Capacitors