Enermax Tomahawk 500 W Power Supply Review

Primary Analysis

On this page we will take an in-depth look at the primary stage of Enermax Tomahawk 500 W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one KBU10J rectifying bridge in its primary, which can deliver up to 10 A at 100° C if a heatsink is used or up to 8 A at 50° C if a heatsink is not installed, which is the case. At 115 V this unit would be able to pull up to 920 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 736 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 bridge.

On the active PFC circuit two STP21NM50N power MOSFET transistors are used, each one capable of delivering up to 18 A at 25° C or up to 11 A at 100° C in continuous mode (note the difference temperature makes), or up to 72 A in pulse mode at 25° C. These transistors present a maximum 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.

Figure 10: Active PFC transistors and diode.

This power supply uses a Chinese capacitor from Samxon labeled at 85° C to filter the output from the active PFC circuit.

In the switching section, two STP11NK50ZFP power MOSFET transistors are used. Each of the transistors is capable of delivering up to 10 A at 25° C or 6.3 A at 100° C in continuous mode, or up to 40 A at 25° C in pulse mode, with an RDS(on) of 520 mΩ, which is very high (thus probably making the power supply to present lower efficiency).

Figure 11: Switching transistors.

The primary is controlled by the omnipresent CM6800 PWM/PFC combo controller.

Figure 12: PWM/PFC combo Controller.

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