Let’s now take an in-depth look on the primary stage from Rocketfish 550 W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.
This power supply uses one KBU10J rectifying bridge on its primary, which can deliver up to 10 A at 75º 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.
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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 25º C or 12.5 A at 100º C (see the difference temperature makes) in continuous mode or up to 60 A in pulse mode at 25º 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.
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Figure 10: Active PFC transistors.
This power supply uses a Japanese capacitor from Chemi-Con labeled at 85º C to filter the output from the active PFC circuit.
On 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.
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Figure 11: PFC/PWM combo controller.
Let’s now take a look on the secondary from this power supply.
