On this page we will take an in-depth look at the primary stage of Scythe Kamariki 4 550 W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one GBU805 rectifying bridge in its primary, which can deliver up to 8 A at 100º C. 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.

Scythe Kamariki 4 550 W uses two SPP20N60C3 power MOSFET transistors on its active PFC circuit, each one capable of delivering up to 20.7 A at 25º C or 13.1 A at 100º C in continuous mode (note the difference temperature makes) or up to 62.1 A at 25º C in pulse mode, presenting a resistance of 160 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 9: Rectifying bridge, active PFC transistors and diode.

The electrolytic capacitor in charge of filtering the active PFC output is Japanese from Chemi-Con and labeled at 105º C. This is great for two reasons. First Japanese capacitors have the best quality and don’t suffer from leakage and second it is better to see caps labeled at 105º C instead of 85º C.

This power supply uses another two SPP20N60C3 power MOSFET transistors on the traditional two-transistor forward configuration on its switching section. The specs for these transistors are published above.

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Figure 10: Switching transistors.

The primary is controlled by a FAN4800I PFC/PWM controller.

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Figure 11: PFC/PWM controller.