On this page we will take an in-depth look at the primary stage of Fusion 550RF. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.
This power supply uses one GBU806 rectifying bridge in its primary stage, which can deliver up to 8 A (rated at 100° C). This is more than adequate rating for a 500 W-550 W power supply. The reason why is that at 115 V this unit would be able to pull up to 920 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 736 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. This component is located on the same heatsink as the switching transistors.
The active PFC circuit from this power supply uses two FQH18N50V2 power MOSFET transistors, which are capable of delivering up to 20 A at 25° C or 12.7 at 100° C in continuous mode, or up to 80 A in pulse mode.
The electrolytic capacitor in charge of filtering the output from the PFC circuit is Japanese from Chemi-Con, which is great.
The PFC circuit is controlled by the omnipresent PFC/PWM controller CM6800, which is located on a small printed circuit board shown in Figure 10.
In the switching section, another two FQH18N50V2 power MOSFET transistors in two-transistor forward configuration are used. The specs for these transistors are published above.