Cooler Master GX 750 W Power Supply Review

Primary Analysis

On this page we will take an in-depth look at the primary stage of Cooler Master GX 750 W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses two GBU1006 rectifying bridges connected in parallel in its primary, each one supporting up to 10 A at 100° C. At 115 V this unit would be able to pull up to 2,300 W from the power grid; assuming 80% efficiency, the bridges would allow this unit to deliver up to 1,840 W without burning themselves out. Nice overspecification! Of course, we are only talking about these components, and the real limit will depend on all the other components in this power supply.

On the active PFC circuit two SPW20N60C3 power MOSFET transistors are used, each one capable of delivering up to 20.7 A at 25° C or 13.1 A at 100° C in continuous mode (note the difference temperature makes), or up to 62.1 A in pulse mode at 25° C. These transistors present a resistance of 190 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 a capacitor from Su’scon labeled at 85° C to filter the output from the active PFC circuit.

In the switching section, two SPP20N60C3 power MOSFETs are used on the traditional two-transistor forward configuration. The specs fo
r these transistors are published above.

Figure 9: Rectifying bridges, switching transistors and active PFC transistors.

The switching transistors are controlled by the famous PFC/PWM combo controller CM6800.

Figure 10: PFC/PWM combo controller.

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