Cooler Master Real Power Pro 850 W Power Supply Review

Primary Analysis

We were very curious to check what components were chosen for the power section of this power supply and also how they were set together, i.e., the design used. We were willing to see if the components could really deliver the power announced by Cooler Master.

From all the specs provided on the databook of each component, we are more interested on the maximum continuous current parameter, given in ampères or amps for short. To find the maximum theoretical power capacity of the component in watts we need just to use the formula P = V x I, where P is power in watts, V is the voltage in volts and I is the current in ampères.

We also need to know under which temperature the component manufacturer measured the component maximum current (this piece of information is also found on the component databook). The higher the temperature, the lower current semiconductors can deliver. Currents given at temperatures lower than 50° C are no good, as temperatures below that don’t reflect the power supply real working conditions.

Keep in mind that this doesn’t mean that the power supply will deliver the maximum current rated for each component as the maximum power the power supply can deliver depends on other components used – like the transformer, coils, the PCB layout, the wire gauge and even the width of the printed circuit board traces – not only on the specs of the main components we are going to analyze.

For a better understanding of what we are talking here, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses two GBU1006 rectifying bridges connected in parallel in its primary stage, which can deliver up to 10 A (rated at 100° C) each, so the AC rectification circuit can handle up to 20 A. This stage is clearly overspec’ed: at 115 V this unit would be able to pull up to 2,300 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 1,840 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.

Figure 9: Rectifying bridges.

This power supply uses two STW25NM50N power MOSFET transistors on its active PFC circuit, which can handle up to 22 A (at 25° C) or 14 A (at 100° C) in continuous mode, or up to 88 A (at 25° C) in pulse mode each.

On the switching section this power supply uses two STW20NM50 power MOSFET transistors in two-transistor forward configuration, which can deliver up to 20 A (at 25° C) or 12.6 A (at 100° C) in continuous mode, or up to 80 A (at 25° C) in pulse mode, which is the mode used.

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

As we mentioned this power supply uses a dual-transformer design. The configuration used is really interesting. Instead of the primaries of the two transformers being connected in parallel, they are connected in series.

The primary section is controlled by a CM6800 integrated circuit, which is a very popular active PFC and PWM controller combo. It is located on a printed circuit board that is located at one of the edges of the power supply.

Figure 11: PFC and PWM controller combo.