Rosewill Libertas 800 W Power Supply Review

Primary Analysis

On this page we will take an in-depth look at the primary stage of the Rosewill Libertas 800 W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses two GBU1006 rectifying bridges connected in parallel, both attached to the same heatsink used by the active PFC transistors and the switching transistors. Each bridge supports up to 10 A at 100° C if a heatsink is used, so in theory, you would be able to pull up to 2,300 W from a 115 V power grid. Assuming 80% efficiency, the bridges would allow this unit to deliver up to 1,840 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 t
his power supply.

Figure 10: Rectifying bridges

The active PFC circuit uses two IXTQ26N50P MOSFETs, each one capable of delivering up to 26 A at 25° C or up to 17 A at 100° C in continuous mode (note the difference temperature makes), or up to 78 A in pulse mode at 25° C. These transistors present a 230 mΩ resistance when turned on, a characteristic called RDS(on). The lower this number the better, meaning that the transistors will waste less power and the power supply will have a higher efficiency.

Figure 11: Active PFC transistors

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 two capacitors with the same total capacitance are physically smaller than a single capacitor with equivalent capacitance. The Rosewill Libertas 800 W uses two 220 µF x 400 V capacitors connected in parallel, the equivalent of one 440 µF x 400 V capacitor. They are manufactured by Teapo and labeled at 85° C.

In the switching section, two SPW24N60C3 MOSFET transistors are used, connected in the traditional two-transistor forward configuration. Each switching transistor is capable of delivering up to 24.3 A at 25° C or 15.4 A at 100° C in continuous mode (see the difference temperature makes), or 72.9 A in pulse mode at 25° C, with an RDS(on) of 160 mΩ.

Figure 12: +5VSB switching transistor, active PFC diode, and the two switching transistors

Unfortunately the manufacturer covered the active PFC/PWM circuit with a black material that was impossible to remove, making it impossible for us to identify the integrated circuit used in this stage.

Figure 13: Active PFC/PWM combo controller

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