Primary Analysis

Let’s now take an in-depth look inside Enermax Liberty DXX 500 W. For a better understanding of what we are talking here and on the next page, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one GBU10J rectifying bridge on its primary stage, which can deliver up to 10 A (rated at 100º C). This bridge is attached to a heatsink.

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Figure 9: Rectifying bridge.

On the active PFC circuit this power supply uses two IRFP460A power MOSFET transistors, each capable of handling up to 20 A at 25º C or 13 A at 100º C (here you can see the difference temperature makes).

On the switching section two 2SK2746 power MOSFET transistors are used, each one capable of delivering up to 7 A at 25º C continuously or 21 A at 25º C in pulse mode.

Here lies the main different between this power supply and other good power supplies available on the market today. Even though the switching section has two transistors, they don’t use the traditional two-transistor forward configuration, but instead the two transistors are connected in parallel using a single-transistor forward configuration.

The switching transistors, active PFC transistors, active PFC diode and +5VSB switching transistor are located on the same heatsink.

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Figure 10: Switching transistor, active PFC transistor and switching transistor from the +5VSB power supply.

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Figure 11: Active PFC diode, active PFC transistor and switching transistor.

The active PFC circuit is controlled by a UCC3818 integrated circuit, which is located on a small printed circuit board attached to the main printed circuit board.

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Figure 12: Active PFC controller.

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