Seasonic X-Series KM3 650 W Power Supply Review

Primary Analysis

On this page, we will take an in-depth look at the primary stage of the Seasonic X-Series KM3 650 W. For a better understanding, please read our “Anatomy of Switching Power Supplies” tutorial.         

This power supply uses two GBJ1506 rectifying brid
ges, which are attached to an individual heatsink. Each bridge supports up to 15 A at 100° C. 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 (or 3,105 W at 90% efficiency). Of course, we are only talking about these particular components. The real limit will depend on all the components combined in this power supply. 

Figure 11: Rectifying bridges

The active PFC circuit uses two IPP60R250CP MOSFETs, each one supporting up to 12 A at 25° C or 8 A at 100° C in continuous mode (note the difference temperature makes), or 40 A at 25° C in pulse mode. These transistors present a 250 mΩ maximum resistance when turned on, a characteristic called RDS(on). The lower the number the better, meaning that the transistor will waste less power, and the power supply will have a higher efficiency.

Figure 12: The active PFC diode and transistors

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

Figure 13: Active PFC controller

The output of the active PFC circuit is filtered by two 220 μF x 420 V Japanese electrolytic capacitors, from Hitachi, labeled at 105° C. These capacitors are connected in parallel and are the equivalent of a single 440 μF x 420 V capacitor.

Figure 14: Capacitors

In the switching section, four IPP50R399CP MOSFETs are employed using a full-bridge, resonant configuration. Each transistor supports up to 9 A at 25° C or 6 A at 100° C in continuous mode or up to 20 A at 25° C in pulse mode, with a maximum RDS(on) of 399 mΩ. 

Figure 15: The switching transistors

The switching transistors are controlled by a CM6901 resonant controller, which is physically located on the same printed circuit board as the +12 V transistors.

Figure 16: Resonant controller

Let’s now take a look at the secondary of this power supply.