As we have mentioned in other articles and reviews, the first place we look when opening a power supply for a hint about its quality is its filtering stage. The recommended components for this stage are two ferrite coils, two ceramic capacitors (Y capacitors, usually blue), one metalized polyester capacitor (X capacitor), and one MOV (Metal-Oxide Varistor). Very low-end power supplies use fewer components, usually removing the MOV and the first coil.

On this power supply this stage is flawless. It has two extra ferrite coils, one extra X capacitor and two extra Y capacitors.

One thing that we noticed here was that the active PFC circuit had actually two circuits working in parallel (see the two coils in Figure 8), and this was the first power supply we’ve seen using such design. We will talk more about this in the next page.

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Figure 7: Transient filtering stage (part 1).

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Figure 8: Transient filtering stage (part 2).

In the next page we will have a more detailed discussion of the components used in the Seasonic M12D 750 W.