Corsair AX850W Power Supply Review

Primary Analysis

On this page we will take an in-depth look at the primary stage of the Corsair AX850W For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses two GBJ1506 rectifying bridges, which are attached to an individual heatsink. Each bridge supports up to 15 A at 100° C so, in theory, you would be able to pull up to 3,450 W from a 115 V power grid. Assuming 80% efficiency, the bridges would allow this unit to deliver up to 2,760 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 this power supply. These are the same bridges used in the X Fanless 400 W and X Series 650 W models from Seasonic.

Figure 10: Rectifying bridges

The active PFC circuit uses three IPP60R160C6 MOSFETs, each one capable of delivering up to 23.8 A at 25° C or up to 15 A at 100° C (note the difference temperature makes) in continuous mode, or up to 70 A in pulse mode at 25° C. These transistors present a 160 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 achieve a higher efficiency. These transistors are a little bit more powerful than the ones used in the Seasonic X-Series 650 W.

Figure 11: Active PFC diode and 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 Corsair AX850W uses two 390 µF x 420 V capacitors connected in parallel, the equivalent of one 780 µF x 420 V capacitor. They are manufactured by Chemi-Con, a Japanese brand, and labeled at 105° C.

The active PFC circuit is controlled by an NCP1654 integrated circuit.

Figure 12: Active PFC controller

In the switching section, another two IPP60R160C6 MOSFETs are used, and their technical specs were already published above. These transistors are more powerful than the ones used in the Seasonic X-Series 650 W.

Figure 13: Switching transistors

The switching transistors are connected using a design called “LLC resonant,” also known as series parallel resonant converter, being controlled by a CM6901 integrated circuit, which operates under PWM (Pulse Width Modulation) mode when the power supply is operating under light load but under FM (Frequency Modulation) mode under other loads.

Figure 14: LLC resonant controller

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