SHARE

## Primary Analysis

On this page we will take an in-depth look at the primary stage of the FSP Aurum Pro 850 W. For a better understanding, please read our “Anatomy of Switching Power Supplies” tutorial.

This power supply uses two LL15XB60 rectifying bridges, which are attached to an individual heatsink. Each bridge supports up to 15 A at 124° C. So in theory, you would be able to pull up to 3,450 W from a 115 V power grid. Assuming 80% efficiency, the bridges would allow this unit to deliver up to 2,760 W without burning themselves out (or 3,105 W with 90% efficiency). Of course, we are only talking about these particular components. The real limit will depend on all the components combined in this power supply.

Figure 10: Rectifying bridges

The active PFC circuit uses three STF26NM60N MOSFETs, each one supporting up to 20 A at 25° C or 12.6 A at 100° C in continuous mode (note the difference temperature makes), or 80 A at 25° C in pulse mode. These transistors present a 165 mΩ 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 11: Active PFC diode and transistors

The active PFC circuit is managed by an ICE2PCS02 active PFC controller.

Figure 12: Active PFC controller

The output of the active PFC circuit is filtered by two 330 µF x 420 V Japanese electrolytic capacitors, from Matsushita (Panasonic), labeled at 105° C and connected in parallel. This is the equivalent of one 660 µF x 420 V capacitor.

In the switching section, two STW26NM60N MOSFETs are employed using a resonant configuration. These transistors have the exact same specifications as the transistors used in the active PFC circuit. The only difference between them is the packaging (TO-220FP vs. TO-247).

Figure 13: Switching transistors

The switching transistors are controlled by a CM6901 resonant controller.

Figure 14: Resonant controller

This power supply uses two transformers with their primary connected in series instead of using a single transformer. This allows the use of two small transformers instead of a single big one, and also provides better cooling. In Figure 15, you can also see the coil required by the resonant design.

Figure 15: The two transformers

Another interesting feature present in the primary of this power supply that is worthwhile mentioning is the presence of a SENZero chip (SEN012DG), which reduces the amount of energy the power supply consumes when in standby mode.

Figure 16: The SENZero chip

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

## Contents

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.