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. On the main AC connector (Figure 8) it has already all the required filtering components and more: four Y capacitors, one X capacitor and two ferrite coils. On the main printed circuit board it has one X capacitor, two Y capacitors and one ferrite coil, plus another X capacitor after the rectifying bridge. There are two MOV’s located after the rectifying bridge behind the two big electrolytic capacitors (not shown in Figure 9) and not before as usual.

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Figure 8: Transient filtering stage (part 1).

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Figure 9: Transient filtering stage (part 2).

In the next page we will have a more detailed discussion of the components used in the Topower PowerBird 900 W.