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Primary Analysis

On this page we will take an in-depth look at the primary stage of the XFX PRO 650 W XXX Edition. For a better understanding, please read our “Anatomy of Switching Power Supplies” tutorial.

This power supply uses two GBU606 rectifying bridges connected in parallel and attached to an individual heatsink. Each bridge supports up to 6 A at 100° C. So, in theory, you would be able to pull up to 1,380 W from a 115 V power grid. Assuming 80% efficiency, the bridges would allow this unit to deliver up to 1,104 W without burning themselves out. Of course, we are only talking about these particular components. The real limit will depend on all the components combined in this power supply.

XFX Pro 650w XXX EditionFigure 11: Rectifying bridges

The active PFC circuit uses three FDP18N50 MOSFETs, each supporting up to 18 A at 25° C or 10.8 A at 100° C in continuous mode (see the difference temperature makes) or 72 A at 25° C in pulse mode. These transistors present a maximum 265 mΩ resistance when turned on, a characteristic called RDS(on). The lower the number the better, meaning that the transistor will waste less power, and the power supply will have a higher efficiency. The PRO 650 W Core Edition uses two 20 A transistors here.

XFX Pro 650w XXX EditionFigure 12: Active PFC transistors

The output of the active PFC circuit is filtered by two 220 µF x 400 V Japanese electrolytic capacitors, from Rubycon, labeled at 105° C. These capacitors are connected in parallel and are the equivalent of a single 440 µF x 400 V capacitor.

XFX Pro 650w XXX EditionFigure 13: Capacitors

In the switching section, another two FDP18N50 MOSFETs are employed using the traditional two-transistor forward configuration. The specifications for these transistors were already discussed above. The PRO 650 W Core Edition uses two 20 A transistors here.

XFX Pro 650w XXX EditionFigure 14: One of the switching transistors and the active PFC diode

The primary is managed by a CM6802 active PFC/PWM combo controller.  

XFX Pro 650w XXX EditionFigure 15: Active PFC/PWM combo controller

Let’s now take a look at the secondary of this power supply.

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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.