Thermaltake Purepower 500 W Power Supply Review

Primary Analysis

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

This power supply uses one GBU806 rectifying bridge, which supports up to 8 A at 100° C if a heatsink is used or only up to 3.5 A at 100° C if a heatsink isn’t used, which is the case. At 115 V this unit would be able to pull up to 403 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 322 W without burning itself out. 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.

The electrolytic capacitors from the voltage doubler circuit are from JunFu.

When analyzing the switching section from Thermaltake Purepower 500 W we had a good surprise. Usually power supplies without active PFC circuit are based on the half-bridge topology, which is currently considered obsolete. This unit, however, uses the two-transistor forward switching configuration, just like power supplies with active PFC, wh
ich – at least in theory – promises higher efficiency.

The switching transistors are from the MOSFET kind (and not “regular” transistors like half-bridge power supplies), with two STP14NK50Z being used. Each transistor can handle up to 14 A at 25° C or up to 7.6 A at 100° C in continuous mode (note the difference temperature makes) or up to 48 A at 25° C in pulse mode. There transistors present a 380 mΩ resistance when turned on, a parameter called RDS(on). The lower this number, the better, meaning that the transistor will consume less and thus present higher efficiency.

Figure 10: Switching transistors.

The switching transistors are controlled by a UC3845B PWM combo controller, which is located on the solder side of the printed circuit board.

Figure 11: PWM controller.

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