On this page we will take an in-depth look at the primary stage of the Cougar RS 650 W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.
This power supply uses one KBU10J rectifying bridge, attached to an individual heatsink. This component supports up to 10 A at 75° C, so in theory, you would be able to pull up to 1,150 W from a 115 V power grid. Assuming 80% efficiency, the bridge would allow this unit to deliver up to 920 W without burning itself out. Of course, we are only talking about this particular component. The real limit will depend on all the components combined in this power supply.
The active PFC circuit uses two MDP18N50 MOSFETs, each supporting up to 18 A at 25° C or 11 A at 100° C in continuous mode (note the difference temperature makes), or 72 A at 25° C in pulse mode. These transistors present a 270 mΩ resistance when turned on, a characteristic called RDS(on). The lower the number the better, meaning that the transistor will
waste less power, and the power supply will have a higher efficiency.
The electrolytic capacitor that filters the output of the active PFC circuit is Japanese, from Chemi-Con, and labeled at 85° C.
In the switching section, another two MDP18N50 MOSFETs are used in the traditional two-transistor forward configuration. The specifications for these transistors were already discussed above.
The primary is controlled by an FAN4800 active PFC/PWM combo controller.
Let’s now take a look at the secondary of this power supply.