SilverStone Element ST50EF-Plus 500 W Power Supply Review

Primary Analysis

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 100° 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.

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 25° C or 10.71 A at 100° C in continuous mode (note the difference temperature makes) or 68 A in pulse mode at 25° 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 105° C, which is great (on the majority of power supplies this component is rated at 85° 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 25° C or 7.6 A at 100° C in continuous mode (note the difference temperature makes) or 48 A in pulse mode at 25° C, with a maximum RDS(on) of 380 mΩ.

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

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

Figure 11: PFC/PWM combo controller.

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