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## Primary Analysis

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

This power supply uses one GBU805 rectifying bridge in its primary, which can deliver 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 this component. Of course we are only talking about this component and the real limit will depend on all other components from the power supply. Interesting enough the 400 W model uses a 10 A bridge here, but since on this other model the bridge isn’t attached to a heatsink, its limit drops to 8 A. The bridge used on OCZ500SXS is exactly the same one used on Zalman ZM460-APS and on SilverStone Strider ST50F.

Figure 9: Rectifying bridge.

On the active PFC circuit two SPA20N60C3 power MOSFET transistors are used, each one capable of delivering up to 20.7 A at 25° C or 13.1 A in continuous mode (note the difference temperature makes) or 62.1 A in pulse mode at 25° C, presenting a resistance of 190 mΩ when turned on, a characteristic called RDS(on) – the lower this number the higher efficiency is. These transistors are more powerful than the ones used on the StealthXStream 400 W model (14 A at 25° C or 7.6 A at 100° C) and are exactly the same ones used on Zalman ZM460-APS and SilverStone Strider ST50F.

Figure 10: Active PFC transistors and diode.

The electrolytic capacitor in charge of filtering the output from the active PFC circuit is from CapXon and labeled at 85° C.

In the switching section, two STF21NM50N power MOSFET transistors are used on the traditional two-transistor forward configuration. These transistors can deliver up to 18 A at 25° C or 11 A at 100° C in continuous mode, or up to 72 A at 25° C in pulse mode, presenting an RDS(on) of 190 mΩ. These are the same components used on SilverStone Strider ST50F. Zalman ZM460-APS uses different transistors here, but with similar specs.

Figure 11: Switching transistors.

The primary is controlled by the omnipresent CM6800 PFC/PWM combo controller.

Figure 12: PFC/PWM combo controller.

In summary, the primaries from OCZ StealthXStream 500 W, Zalman ZM460-APS and SilverStone Strider ST50F are identical. Now let’s see the secondary.

## Contents

Gabriel Torres is a Brazilian best-selling ICT expert, with 24 books published. He started his online career in 1996, when he launched Clube do Hardware, which is one of the oldest and largest websites about technology in Brazil. He created Hardware Secrets in 1999 to expand his knowledge outside his home country.