PC Power & Cooling Silencer Mk II 750 W Power Supply Review

Primary Analysis

On this page we will take an in-depth look at the primary stage of PC Power & Cooling Silencer Mk II 750 W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses two GBJ1506 rectifying bridges on its primary, but they are not attached to a heatsink. Each bridge supports up to 15 A at 100° C, so in theory, you wo
uld be able to pull up to 3,450 W from the power grid. Assuming 80% efficiency, the bridges would allow this unit to deliver up to 2,760 W without burning themselves out. Of course, we are only talking about these components, and the real limit will depend on all the other components in this power supply.

Figure 10: Rectifying bridges.

The active PFC circuit uses two SPW24N60C3 MOSFETs, each one capable of delivering up to 24.3 A at 25° C or 15.4 A at 100° C in continuous mode (note the difference temperature makes) or 72.9 A in pulse mode at 25° C. These transistors present a 160 mΩ resistance when turned on, a characteristic called RDS(on). The lower this number the better, meaning that the transistors will waste less power and the power supply will achieve a higher efficiency.

Figure 11: Active PFC transistors.

This power supply uses two electrolytic capacitors to filter the output from the active PFC circuit. The use of more than one capacitor here has absolute nothing to do with the “quality” of the power supply, as laypersons may assume (including people without the proper background in electronics doing power supply reviews around the web). Instead of using one big capacitor, manufacturers may choose to use two or more smaller components that will give the same total capacitance, in order to better accommodate space on the printed circuit board, as two or more capacitors with small capacitance are physically smaller than one capacitor with the same total capacitance. PC Power & Cooling Silencer Mk II 750 W uses two 390 µF x 400 V capacitors connected in parallel; this is the equivalent of one 780 µF x 400 V capacitor.

These capacitors are Japanese, from Chemi-Con, and are labeled at 105° C. This is good for two reasons: first, Japanese capacitors do not leak; and second, usually manufacturers use 85° C capacitors here, so it is good to see a manufacturer using a capacitor with a higher temperature rating.

In the switching section, another two SPW24N60C3 power MOSFET transistors are used. The specs for these transistors were already published above.

Figure 12: Active PFC diodes and one of the switching transistors.

This power supply uses the famous CM6800 active PFC/PWM combo controller in its primary.

Figure 13: Active PFC/PWM combo controller.

Now let’s take a look at the secondary from this power supply.