Let’s now take an in-depth look on the primary stage from PC Power & Cooling Silencer 750 Quad. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.
This power supply uses one GBJ1506 rectifying bridge on its primary, which can deliver up to 15 A (rated at 100º C). As you can see on Figure 9 this bridge is attached to a heatsink. This component is clearly overspec'ed: at 115 V this unit would be able to pull up to 1,725 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 1,380 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.
The active PFC circuit uses two SPW35N60C3 power MOSFET transistors, each one capable of handling up to 21.9 A in continuous mode at 100º C (or 34.6 A at 25º C; see the difference temperature makes) or 103.8 A in pulse mode at 25º C. These transistors are located on the same heatsink as the switching transistors.
On the switching section this power supply uses two SPP24N60C3 power MOSFET transistors in the traditional two-transistor forward configuration. Each transistor is capable of handling up to 15.4 A at 100º C in continuous mode (or 24.3 A at 25º C) or up to 72.9 A in pulse mode at 25º C.
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Figure 10: Active PFC transistors (left), active PFC diode and switching transistors (right).
The primary section of this power supply is controlled by a UCC28515DW integrated circuit, which is a PFC/PWM controller combo. This integrated circuit is located on a small printed circuit board attached to the main printed circuit board.
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Figure 11: Active PFC/PWM controller combo.
