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Primary Analysis

On this page we will take an in-depth look at the primary stage of Seasonic S12II Bronze 520 W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one GBU806 rectifying bridge in its primary, which can deliver up to 8 A at 100° C. 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.

Seasonic S12II Bronze 520 W power supplyFigure 9: Rectifying bridge.

On the active PFC circuit two FDP18N50 power MOSFET transistors are used, each one capable of delivering up to 18 A at 25° C or up to 10.8 A at 100° C in continuous mode (note the difference temperature makes), or up to 72 A in pulse mode at 25° C. These transistors present a maximum resistance of 265 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.

Seasonic S12II Bronze 520 W power supplyFigure 10: One of the switching transistors, active PFC diode and active PFC transistors.

This power supply uses a Japanese capacitor from Chemi-Con labeled at 105° C to filter the output from the active PFC circuit. This is great because Japanese capacitors are better and being labeled at 105° C means a higher life-span. At Seasonic’s website there is something fishy, though. The manufacturer added a comparison graph between solid capacitors and conventional electrolytic capacitors, but this power supply doesn’t have any solid capacitor in it. The presence of this chart is very misleading.

In the switching section, another two FDP18N50 power MOSFET transistors are used. The main specifications for these transistors were already published above.

The primary is controlled by an ICE1CS02 PWM/PFC combo controller.

Seasonic S12II Bronze 520 W power supplyFigure 11: PWM/PFC combo Controller.

Now let’s 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.