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 100º 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.

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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 25º C or 13.1 A at 100º C in continuous mode (note the difference temperature makes) or 62.1 A in pulse mode at 25º 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 85º C.

In the switching section, another two SPW20N60C3 power MOSFET transistors are used on the traditional two-transistor forward configuration.

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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.

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Figure 11: Active PFC/PWM combo controller.

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