Let’s now take an in-depth look on the primary stage from PowerBird 900 W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one GBJ2506 rectifying bridge on its primary, which can deliver up to 25 A at 100º. This component is clearly overspec’ed: at 115 V this unit would be able to pull up to 2,875 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 2,300 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.

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Figure 10: Rectifying bridge.

On the active PFC circuit two SPW35N60C3 power MOSFET transistors are used, each one capable of delivering up to 34.6 A at 25º C or 21.9 A at 100º C in continuous mode (see the difference temperature makes) or 103.8 A in pulse mode at 25º C.

This power supply uses two electrolytic capacitors to filter the output from the active PFC circuit. The use of more than one capacitor here has absolute nothing to do with the “quality” of the power supply, as laypersons may assume (including people without the proper background in electronics doing power supply reviews around the web). Instead of using one big capacitor manufacturers may choose to use two or more smaller components that will give the same total capacitance, in order to better accommodate space on the printed circuit board, as capacitors with small capacitance are physically smaller than capacitors with bigger capacitances. On PowerBird 900 W two 1200 µF x 200 V capacitors are used in series; this is equivalent of one 600 µF x 400 V capacitor.

These capacitors are Japanese from Toshin Kogyo (TK) and are labeled at 105º C. This is good for two reasons, first Japanese capacitors do not leak and second usually manufacturers use 85º C capacitors here, so it is good to see a manufacturer using a capacitor with a higher temperature rating.

On the switching section another two SPW35N60C3 power MOSFET transistors are used on the traditional two-transistor forward configuration. The specs for these transistors we’ve already published above. These two transistors drive the two available transformers.

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Figure 11: Active PFC transistors, active PFC diodes and switching transistors.

This power supply uses the omnipresent CM6800 active PFC/PWM combo controller.

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Figure 12: Active PFC/PWM combo controller.

Let’s now take a look on the secondary from this power supply.