On this page we will take an in-depth look at the primary stage of SilverStone Element ST50EF-Plus. 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 STW20NK50Z power MOSFET transistors are used, each one capable of delivering up to 17 A at 25º C or 10.71 A at 100º C in continuous mode (note the difference temperature makes) or 68 A in pulse mode at 25º C, presenting a resistance of 270 mΩ when turned on, a characteristic called RDS(on) – the lower this number the higher efficiency is.

The electrolytic capacitor in charge of filtering the output from the active PFC circuit is Taiwanese from Teapo and labeled at 105º C, which is great (on the majority of power supplies this component is rated at 85º C, the higher temperature rating the better – it translates into a higher life-span for the product).

In the switching section, two STW14NK50Z power MOSFET transistors are used on the traditional two-transistor forward configuration. Each one is capable of delivering up to 14 A at 25º C or 7.6 A at 100º C in continuous mode (note the difference temperature makes) or 48 A in pulse mode at 25º C, with a maximum RDS(on) of 380 mΩ.

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Figure 10: Switching transistors, active PFC diode and active PFC transistors.

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

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Figure 11: PFC/PWM combo controller.

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