Primary Analysis
Contents
On this page we will take an in-depth look at the primary stage of the Cougar A-Series 560 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.
Figure 10: Rectifying bridge
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 te
mperature 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.
Figure 11: Active PFC transistors and diode
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.
Figure 12: One of the switching transistors
The primary is controlled by an FAN4800 active PFC/PWM combo controller.
Figure 13: Active PFC/PWM combo controller
The primary of the A-Series 560 W is identical to the primary of the Cougar RS 650 W.
Let’s now take a look at the secondary of this power supply.
