Let’s now take an in-depth look on the primary stage from Rocketfish 700 W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one T15XB80 rectifying bridge on its primary, capable of delivering up to 15 A at 100º C with a heatsink, which is the case.

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Figure 8: Rectifying bridge.

The active PFC circuit uses two SPW20N60C3 power MOSFET transistors, each one capable of handling up to 13.1 A in continuous mode at 100º C (or 20.7 A at 25º C; see the difference temperature makes) or 62.1 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 regular power NPN transistors and not power MOSFET transistors. This kind of transistor is only used on power supplies with old project and the main problem of using this kind of transistor is usually efficiency, as they consume more power for their own operation compared to FET/MOSFET transistors. Two 2SC3320 are used, each one capable of delivering up to 15 A at 25º C.

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Figure 9: Switching transistors, PFC diode and active PFC transistor (the other active PFC transistor is on the other side of the heatsink).

The primary section is controlled two separated integrated circuits, one for the active PFC circuit (ICE2PCS01) and one for driving the switching transistor (i.e. PWM, AZ7500B integrated circuit), instead of using just one combo controller as it happens with almost all modern power supplies.

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Figure 10: Active PFC controller.