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## Primary Analysis

On this page, we will take an in-depth look at the primary stage of the SilverStone ST45SF-G. For a better understanding, please read our “Anatomy of Switching Power Supplies” tutorial.

This power supply uses one GBU1006 rectifying bridge, which is attached to an individual heatsink. This bridge supports up to 10 A at 100° C. In theory, you would be able to pull up to 1,150 W from a 115 V power grid. Assuming 80% efficiency, the bridge would allow this unit to deliver up to 1,380 W without burning itself out (or 1,553 W at 90% efficiency). Of course, we are only talking about this particular component. The real limit will depend on all the components combined in this power supply.

Figure 11: Rectifying bridge

The active PFC circuit uses one IPW50R140CP MOSFETs, which supports up to 23 A at 25° C or 15 A at 100° C in continuous mode (note the difference temperature makes), or 56 A at 25° C in pulse mode. This transistor presents a 140 mΩ maximum resistance when turned on, a characteristic called RDS(on). The lower the number the better, meaning that the transistor will waste less power, and the power supply will have a higher efficiency.

Figure 12: The active PFC diode and the active PFC transistor

The active PFC circuit is managed by a CM6502 active PFC controller.

The output of the active PFC circuit is filtered by one 330 µF x 450 V Japanese electrolytic capacitor from Panasonic, labeled at 105° C.

Figure 13: Capacitor

In the switching section, two STP20NM50FD MOSFETs are employed using a resonant configuration. Each transistor supports up to 20 A at 25° C or 14 A at 100° C in continuous mode or up to 80 A at 25° C in pulse mode, with a maximum RDS(on) of 250 mΩ.

Figure 14: Switching transistors

The switching transistors are controlled by a CM6901 controller.

Figure 15: Resonant controller (left) and active PFC controller (right)

Let’s now take a look at the secondary of this power supply.

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.