Let’s now take an in-depth look on the primary stage from Corsair CX400W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.
This power supply uses one GBU806 rectifying bridge on its primary, which can deliver up to 8 A at 100º C. This component is clearly overspec’ed: 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.
On the active PFC circuit two FDP18N50 power MOSFET transistors are used, each one capable of delivering up to 18 A at 25º C or 10.8 A at 100º C (see the difference temperature makes) in continuous mode or up to 72 A in pulse mode at 25º C. These transistors present a resistance of 265 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: Active PFC transistors and diode.
This power supply uses a Japanese capacitor from Hitachi labeled at 85º C to filter the output from the active PFC circuit.
On the switching section two FQP13N50C power MOSFET transistors are used on the traditional two-transistor forward configuration. Each one is capable of delivering up to 13 A at 25º C or 8 A at 100º C (see the difference temperature makes) in continuous mode or up to 52 A in pulse mode at 25º C. These transistors present an RDS(on) of 480 mΩ (too high in our opinion).
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Figure 10: Rectifying bridge and switching transistors.
The rectifying bridge is the same model used on Corsair VX450W, Antec EarthWatts 500 W and Arctic Cooling Fusion 550RF, however the PFC and switching transistors from CX400W’s primary have lower current limit.
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.
