Cooler Master eXtreme Power Plus 400 W Power Supply Review

Primary Analysis

On this page we will take an in-depth look at the primary stage of Cooler
Master eXtreme Power Plus 400 W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses two GBL06 rectifying bridges, each one supporting up to 4 A at 50° C if a heatsink is used, which is not the case, or up to 3 A at 40° C. At 115 V this unit would be able to pull up to 690 W from the power grid; assuming 80% efficiency, the bridges would allow this unit to deliver up to 552 W without burning themselves out. Of course, we are only talking about these components, and the real limit will depend on all the other components in this power supply. Both the 460 W and 500 W versions of this power supplies use two 6 A bridges here.

Figure 9: Rectifying bridges.

This unit is based on a single-transistor forward topology, which is good to see, since usually low-end units are based on the obsolete half-bridge design. Two 2SK4115 power MOSFET transistors are connected in parallel on the switching section. Each transistor is capable of handling up to 7 A at 25° C in continuous mode, or up to 21 A at 25° C in pulse mode, so the switching section can deliver up to 14 A at 25° C. Unfortunately the manufacturer does not provide the current limits at 100° C. These transistors present an RDS(on) of 1.6 Ω, which is very high (i.e., bad, low efficiency). This number measures the resistance provided by the transistors when they are turned on; the lower this number, the better (higher efficiency). The 460 W model uses different transistors here but with the same current limits, while the 500 W model uses more powerful 9 A transistors here.

Figure 10: One of the switching transistors.

The switching transistors are controlled by a UC3843 PWM controller, which is located on the primary.

Figure 11: PWM controller.

The two electrolytic capacitors from the voltage doubler are from Elite and labeled at 85° C.

Now let’s take a look at the secondary of this power supply.