Nexus RX-8500 850 W Power Supply Review
Primary Analysis
Contents
On this page we will take an in-depth look at the primary stage of Nexus RX-8500. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.
This power supply uses two GBU1006 rectifying bridges connected in parallel, which one supporting up to 10 A at 100° C, if a heatsink is used, which is the case (without a heatsink the current limit drops to 3.2 A). So in theory you would be able to pull up to 2,300 W from a 115 V power grid; assuming 80% efficiency, this bridge would allow this unit to deliver up to 1,840 W without burning. Of course, we are only talking about these components, and the real limit will depend on all the other components in this power supply.
Figure 9: Rectifying bridge.
On the active PFC circuit three SPW20N60C3 power MOSFET transistors are used, each one capable of delivering up to 20.7 A at 25° C or 13.1 A at 100° C in continuous mode (note the difference temperature makes) or 62.1 A in pulse mode at 25° C, presenting a resistance of 190 mΩ when turned on, a characteristic called RDS(on) – the lower this number the higher efficiency is.
The electrolytic capacitor in charge of filtering the output from the active PFC circuit is Taiwanese from Teapo and labeled at 85° C.
In the switching section, another two SPW20N60C3 power MOSFET transistors are used on the traditional two-transistor forward configuration.
Figure 10: +5VSB switching transistor, two of the active PFC transistors and switching transistors.
This power supply uses the famous CM6800 active PFC/PWM combo controller.
Figure 11: Active PFC/PWM combo controller.
Now let’s take a look at the secondary of this power supply.