On this page we will take an in-depth look at the primary stage of the Cooler Master Silent Pro Gold 800 W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one GBU1006 rectifying bridge in its primary, supporting up to 10 A at 100º C. This bridge is attached to the same heatsink used by the primary transistors. At 115 V this unit would be able to pull up to 1,150 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 920 W without burning itself. Of course we are only talking about this component and the real limit will depend on all other components from the power supply.

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Figure 10: Rectifying bridge.

In the active PFC circuit two STW25NM50N power MOSFET transistors are used, each one capable of delivering up to 22 A at 25º C or 14 A at 100º C in continuous mode (note the difference temperature makes), or up to 88 A in pulse mode at 25º C. These transistors present a resistance of 140 mΩ when turned on, a characteristic called RDS(on). This number indicates the amount of power that is wasted, so the lower this number the better, as less power will be wasted, thus increasing efficiency.

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 absolutely 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. Cooler Master Silent Pro Gold 800 W uses two 270 µF x 420 V capacitors in parallel; this is equivalent of one 540 µF x 420 V capacitor. These capacitors are Japanese, from Matsushita (i.e., Panasonic) and labeled at 85º C. It would be nice if Cooler Master had added capacitors rated at 105º C here.

In the switching section, another two STW25NM50N power MOSFETs are used in a slightly modified two-transistor forward configuration. In the standard two-transistor design, two transistors and two diodes are used; in this power supply one of the diodes was replaced by a MOSFET transistor, and this was probably done to increase efficiency.

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Figure 11: Switching transistor, transistor used to replace one of the diodes, switching transistor, active PFC diode and active PFC transistors.

The switching transistors are controlled by a CM6802 PFC/PWM combo controller.

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Figure 12: Daughter board containing the PFC/PWM controller on the primary side and the monitoring circuit on the secondary side.

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Figure 13: PFC/PWM combo controller.

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