Let’s now take an in-depth look on the primary stage from eXtreme Power Plus 500 W. 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. 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 9: Rectifying bridges.

On the switching section this power supply uses two 2SK2611 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. At least this power supply isn’t based on the half-bridge design using bipolar transistors, which is outdated. Each 2SK2611 can drive up to 9 A in continuous mode or up to 27 A in pulse mode (which is the mode used), so the maximum current the switching section can drive is 18 A in continuous mode or 54 A in pulse mode. All values were measured at 25º C. Here eXtreme Power Plus 500 W is different from the 460 W model, which uses the same design but with transistors with lower current limits (7 A each).

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Figure 10: Switching transistors.

The primary is controlled by a UC3843B PWM controller.