Let’s now take an in-depth look on the primary stage from Cooler Master eXtreme Power Plus 460 W (RS-460-PMSR-A3). For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses two GBU605 rectifying bridges connected in parallel on its primary stage. Each bridge can deliver up to 6 A (rated at 100º C), for a total of 12 A at 100º C. This stage is clearly overspec’ed, as power supplies from this power range usually use only one 6 A or 8 A bridge. At 115 V this unit would be able to pull up to 1,380 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 1,104 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. The bridges don’t use a heatsink, which can lower the maximum current they can deliver.

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Figure 8: Rectifying bridges.

On the switching section this power supply uses two 2SK2749 power MOSFET transistors in parallel in a single-transistor forward configuration. Most modern power supplies use a different configuration, two-transistor forward, which is more efficient. Each 2SK2749 can drive up to 7 A in continuous mode or up to 21 A in pulse mode (which is the mode used), so the maximum current the switching section can drive is 14 A in continuous mode or 42 A in pulse mode. All values were measured at 25º C.

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Figure 9: Switching transistors.

As we mentioned on the introduction, this power supply does not have PFC (Power Factor Correction), a feature that provides a better usage from the power grid. Only the European version of this power supply, called RS-460-PMSP-A3, has a passive PFC. Passive PFC is achieved by adding a transformer on the primary section of the power supply.