OCZ ModXStream Pro 500 W Power Supply Review

Primary Analysis

On this page we will take an in-depth look at the primary stage of OCZ ModXStream Pro 500 W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one GBU805 rectifying bridge, which supports up to 8 A at 100° C if a heatsink is used, which is the case. At 115 V this unit would be able to pull up to 920 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 736 W without burning itself out. Of course we are only talking about this component and the real limit will depend on all other components from the power supply. The 600 W model uses a 10 A bridge here.

Figure 9: Rectifying bridge.

Two SPP20N60C3 power MOSFETs are used on the active PFC circuit, 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 at 25° C in pulse mode. These transistors present a maximum 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. The 600 W model uses the same transistors but with a bigger packaging (TO-247 vs. TO-220), which improves heat transfer.

Figure 10: Active PFC transistors and diode.

The electrolytic capacitor used to filter the output from the active PFC circuit is from CEC and labeled at 85° C.

The reviewed power supply uses another two SPP20N60C3 power MOSFETs on its switching section, installed on the traditional two-transistor forward configuration. The specs for these transistors were already published above. The 600 W model uses different transistors here, but similar specs.

Figure 11: Switching transistors.

The primary is controlled by the famous CM6800 PFC/PWM combo controller. The 600 W model we reviewed used a different chip (FAN4800), which is basically the same chip from a different vendor.

Figure 12: PFC/PWM combo controller.

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