Rocketfish 550 W Power Supply Review

Primary Analysis

On this page we will take an in-depth look at the primary stage of Rocketfish 550 W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one KBU10J rectifying bridge in its primary, which can deliver up to 10 A at 75° 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 t
his 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 FCPF20N60 power MOSFET transistors are used, each one capable of delivering up to 20 A at 25° C or 12.5 A at 100° C in continuous mode (note the difference temperature makes), or up to 60 A in pulse mode at 25° C. These transistors present a resistance of 150 mΩ when turned on, a characteristic called RDS(on). This number indicates the amount of power that is wasted, so the lower this number the better, as less power will be wasted thus increasing efficiency.

Figure 10: Active PFC transistors.

This power supply uses a Japanese capacitor from Chemi-Con labeled at 85° C to filter the output from the active PFC circuit.

In the switching section, another two FCPF20N60 power MOSFET transistors are used on the traditional two-transistor forward configuration. The specs for these transistors we already published above.

The primary is controlled by the “famous” CM6800 PFC/PWM combo controller.

Figure 11: PFC/PWM combo controller.

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