Let’s now take an in-depth look on the primary stage from Antec TruePower Quattro 850 W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.
This power supply uses two GBU1005 rectifying bridges connected in parallel on its primary, each one capable of delivering up to 10 A at 100º C, so the total capacity is of 20 A at 100º C. These two bridges are attached to a heatsink.
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Figure 10: Rectifying bridges.
The active PFC circuit uses two STW25NM50N power MOSFET transistors, each one capable of handling up to 14 A in continuous mode at 100º C (or 22 A at 25º C; see the difference temperature makes) or 88 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 a rather different design. It uses a modified single-transistor forward configuration using a second transistor in the place of the required diode. The main transistor is a STW15NK90Z, capable of delivering up to 9.5 A continuously at 100º C (or 15 A at 25º C; once again see the difference temperature makes) or 60 A in pulse mode at 25º C. The second transistor that was installed replacing the diode is a FQPF8N80C, which can deliver up to 5.1 A at 100º C (8 A at 25º C) continuously or up 32 A in pulse mode.
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Figure 11: Switching transistor, support transistor, PFC diode and active PFC transistors.
The primary section is controlled two separated integrated circuits, one for the active PFC circuit (ICE1PCS02) and one for driving the switching transistor (i.e. PWM, NCP1280), instead of using just one combo controller as it happens with almost all modern power supplies. These integrated circuits are located on separated small printed circuit boards that are attached to the main printed circuit board.
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Figure 12: Active PFC controller.
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Figure 13: PWM controller.
