Let’s now take an in-depth look on the primary stage from Nexus RX-6300. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.
This power supply uses one GBU1006 rectifying bridge on its primary, which can deliver up to 10 A at 100º C if a heatsink is used, which is the case, or only 3.2 A if a heatsink is not used. This component is clearly overspec’ed: at 115 V this unit would be able to pull up to 1,150 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 920 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.
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Figure 9: Rectifying bridge.
Ultra X4 500 W uses only one transistor on its active PFC circuit instead of two. An SPW24N60C3 power MOSFET transistors is used, capable of delivering up to 24.3 A at 25º C or 15.4 A at 100º C (see the difference temperature makes) in continuous mode or up to 72.9 A in pulse mode at 25º C, with a resistance of 160 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.
This power supply uses a Taiwanese capacitor from Teapo labeled at 85º C to filter the output from the active PFC circuit. Interesting enough the 850 W model uses a Japanese capacitor here.
On the switching section two STP20NM50FP power MOSFET transistors are used on the traditional two-transistor forward configuration, each one supporting up to 20 A at 25º C or up to 12.6 A at 100º C in continuous mode or up to 80 A at 25º C in pulse mode, with an RDS(on) of 250 mΩ.
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Figure 10: One of the switching transistors, active PFC diode and active PFC transistor.
The primary is controlled by a tiny version of the famous CM6800 PFC/PWM combo controller.
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Figure 11: PFC/PWM combo controller.
Let’s now take a look on the secondary from this power supply.
