Seasonic X-Series 750 W Power Supply Review

Secondary Analysis

The Seasonic X-Series 750 W uses a synchronous design, meaning that the rectifiers were replaced with MOSFETs. Also, this power supply uses a DC-DC design, meaning that it is basically a +12 V power supply, with the +5 V and +3.3 V outputs being generated through two smaller switching power supplies connected to the +12 V rail. Both designs are used to increase efficiency.

The +12 V output uses four IPD031N06L3 G MOSFETs, each 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 3.1 mΩ. These transistors are located on the solder side of the main printed circuit board, using the power supply case as a heatsink. These transistors are identical to the ones used in the 850 W model, which are stronger than the ones used in the 650 W version of this power supply. 

Figure 14: The +12 V transistors

The DC-DC converters are located on the same printed circuit board as the modular cabling system. Both are managed by an APW7159 PWM controller, with each output using a pair of APM2510N MOSFETs, each supporting up to 50 A at 25° C or 35 A at 100° C in continuous mode, with a maximum RDS(on) of 8.5 mΩ, and a pair of APM2556N MOSFETs, each supporting up to 160 A at 25° C or 90 A at 100° C in continuous mode, with a maximum RDS(on) of 4.5 mΩ.

Figure 15: The DC-DC converter

Figure 16: The DC-DC converter

The outputs of this power supply are monitored by a PS223 integrated circuit, which supports over voltage (OVP), under voltage (UVP), and over current (OCP) protections. There are two +12 V over current protection channels; however, the manufacturer decided to configure this power supply as a single-rail model.

Figure 17: Monitoring circuit

This power supply uses a mix of Japanese electrolytic capacitors, from Chemi-Con, and solid capacitors to filter its outputs.

In summary, the secondary of the X-Series 750 W is identical to the one from the X-Series 850 W, with stronger transistors than the secondary of the X-Series 650 W.