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

This power supply uses one GBJ1506 rectifying bridge in its primary, which can deliver up to 15 A at 100º C if a heatsink is used, which is the case (without a heatsink the limit drops to 3 A at 25º C). At 115 V this unit would be able to pull up to 1,725 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 1,380 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. This is the same bridge used on Silencer 610 EPS12V from PC Power & Cooling, which this unit is derived from.

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Figure 11: Rectifying bridge.

On the active PFC circuit two SPP24N60C3 power MOSFET transistors are used, each one capable of delivering up to 24.3 A at 25º C or 15.3 A at 100º C in continuous mode (note the difference temperature makes), or up to 72.9 A in pulse mode at 25º C. These transistors present a resistance of 160 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. These transistors are more powerful than the ones used on Silencer 610 EPS12V from PC Power & Cooling (20.7 A, 13.1 A and 62.1 A, respectively).

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Figure 12: Active PFC transistors, active PFC diode and switching transistors.

This power supply uses a Japanese capacitor from Chemi-Con labeled at 105º C to filter the output from the active PFC circuit, which is excellent (Japanese capacitors are better and being labeled at 105º C is better than being labeled at 85º C).

In the switching section, two FDP18N50 power MOSFET transistors are used, connected on the traditional two-transistor forward configuration. Each of the transistors is capable of delivering up to 18 A at 25º C or 10.8 A at 100º C in continuous mode, or up to 72 A at 25º C in pulse mode, with an RDS(on) of 265 mΩ. Silencer 610 EPS12V use different transistors here (FQP18N50V2), which has a higher continuous current at 100º C (12.1 A).

The primary is controlled by a PFC/PWM combo integrated circuit, a UCC28515DW, which is exactly the same circuit used on Silencer 610 EPS12V from PC Power & Cooling.

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Figure 13: PFC/PWM combo controller.

In summary, the primary from XFX 650 W XXX Edition is similar to the one from PC Power & Cooling 610 EPS12V, with the unit from XFX using more powerful transistors on the active PFC circuit and the model from PC Power & Cooling using transistors on the switching section with a little bit higher current specs.

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