Seasonic S12II Bronze 430 W Power Supply Review

Primary Analysis

On this page we will take an in-depth look at the primary stage of the Seasonic S12II Bronze 430 W. For a better understanding, please read our “Anatomy of Switching Power Supplies” tutorial.

This power supply uses one GBU806 rectifying bridge, which is attached to an individual heatsink. This bridge supports up to 8 A at 100° C. So, in theory, you would be able to pull up to 920 W from a 115 V power grid. Assuming 80% efficiency, the bridge would allow this unit to deliver up to 736 W without burning itself out. Of course, we are only talking about this particular component. The real limit will depend on all the components combined in this power supply.

Figure 10: Rectifying bridge

The active PFC circuit uses two FDP18N50 MOSFETs, each supporting up to 18 A at 25° C or 10.8 A at 100° C in continuous mode (see the difference temperature makes) or 72 A at 25° C in pulse mode. These transistors present a maximum 265 mΩ 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.

The output of the active PFC circuit is filtered by one 390 µF x 400 V Japanese electrolytic capacitor, from Chemi-Con, labeled at 105° C.

In the switching section, another two FDP18N50 MOSFETs are employed using the traditional two-transistor forward configuration. The specifications for these transistors were already discussed above.

Figure 11: One of the switching transistors, the active PFC diode, and the active PFC transistors

The primary is managed by an ICE1CS02 active PFC/PWM combo controller.

Figure 12: Active PFC/PWM combo controller

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