As we mentioned on other articles and reviews, the first place we like to take a look when opening a power supply to have a hint about its quality is its filtering stage. The recommend 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 than that, 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 on Figure 8), and this was the first power supply we’ve seen using such design. We will talk more about this on next page.

click to enlarge
Figure 7: Transient filtering stage (part 1).

click to enlarge
Figure 8: Transient filtering stage (part 2).

Now let’s have a more detailed discussion on the components used on Seasonic M12D 750 W.