Let’s now take an in-depth look on the primary stage from Cooler Master UCP 700 W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses two GBU806 rectifying bridges connected in parallel, each one capable of delivering up to 8 A at 100º C. This section is clearly overspec’ed: at 115 V this unit would be able to pull up to 1,840 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 1,472 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 9: Rectifying bridges.

On the active PFC circuit two SPP20N60C3 power MOSFET transistors are used, each one capable of delivering up to 20.7 A at 25º C or 13.1 A at 100º C (see the difference temperature makes) in continuous mode or up to 62.1 A in pulse mode at 25º C. These transistors present a resistance of 190 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.

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. UCP 700 W uses one 330 µF x 400 V and one 270 µF x 400 V capacitor connected in parallel; this is equivalent of one 600 µF x 400 V capacitor.

These capacitors are Japanese from Chemi-Con and are labeled at 85º C.

On the switching section another two SPP20N60C3 power MOSFET transistors are used on the traditional two-transistor forward configuration. The specs for these transistors are already published above.

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Figure 10: Switching transistors, active PFC diode and transitor.

The primary is controlled by a FAN4800I 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.