On this page we will take an in-depth look at the primary stage of Seventeam ST-380PAS. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one GBU1006 rectifying bridge in its primary, which can deliver up to 10 A at 100º C. This component is clearly overspec’ed: at 115 V this unit would be able to pull up to 1,150 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 920 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.

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Figure 9: Rectifying bridge.

On the active PFC circuit two 2SK3568 power MOSFET transistors are used, each one capable of delivering up to 12 A at 25º C or 48 A in pulse mode at 25º C.

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Figure 10: Active PFC transistors.

The active PFC capacitor is Samxon and labeled at 105º C. Usually manufacturers use 85º C capacitors here, so it is good to see a manufacturer using a capacitor with a higher temperature rating.

In the switching section, two SPA20N60C3 power MOSFET transistors are used on the traditional two-transistor forward configuration. Each one is capable of delivering up to 20.7 A at 25º C or 13.1 A at 100º C in continuous mode (note the difference temperature makes) or 62.1 A in pulse mode at 25º C.

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Figure 11: Switching transistors.

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

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Figure 12: PFC/PWM combo controller.

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