Seasonic X-400 Fanless Power Supply Review

Primary Analysis

On this page we will take an in-depth look at the primary stage of the Seasonic X-400 Fanless. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses two GBJ1506 rectifying bridges, which are attached to an individual heatsink. Each bridge supports up to 15 A at 100° C so, in theory, you would be able to pull up to 3,450 W from a 115 V power grid. Assuming 80% efficiency, the bridges would allow this unit to deliver up to 2,760 W without burning themselves out. Of course, we are only talking about these components, and the real limit will depend on all the other components in this power supply.

Figure 10: Rectifying bridges

The active PFC circuit uses three SPP20N60C3 MOSFETs, each one capable of delivering up to 20.7 A at 25° C or up to 13.1 A at 100° C (note the difference temperature makes) in continuous mode, or up to 62.1 A in pulse mode at 25° C. These transistors present a 190 mΩ resistance when turned on, a characteristic called RDS(on). The lower this number the better, meaning that the transistors will waste less power and the power supply will achieve a higher efficiency.

Figure 11: Active PFC diode and transistors

The electrolytic capacitor used to filter the output of the active PFC circuit is Japanese, from Chemi-Con, and labeled at 105° C.

The active PFC circuit is controlled by an NCP1654 integrated circuit.

Figure 12: Active PFC controller

In the switching section, two IPP60R190C6 MOSFET transistors are used, each one capable of delivering up to 20.2 A at 25° C or up to 12.8 A at 100° C, in continuous mode, or up to 59 A at 25° C in pulse mode, with an RDS(on) of 190 mΩ.

Figure 13: Switching transistors

The switching transistors are connected using a design called “LLC resonant,” also known as series parallel resonant converter, being controlled by a CM6901 integrated circuit, which operates under PWM (Pulse Width Modulation) mode when the power supply is operating under light load but under FM (Frequency Modulation) mode under other loads.

Figure 14: LLC resonant controller

Now let’s take a look at the secondary of this power supply.