Let’s now take an in-depth look on the primary stage from ST-550P-AM. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.
This power supply uses one GBU1006 rectifying bridge on its primary, capable of delivering up to 10 A at 100º C. This component is clearly overspec'ed: at 115 V this unit would be able to pull up to 1,150 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 920 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 SPW16N50C3 power MOSFET transistors, each one capable of handling up to 48 A @ 25º C in pulse mode (which is the case) or up to 16 A @ 25º C or 10 A @ 100º C (see the difference temperature makes).
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Figure 10: Active PFC transistors and diode.
The electrolytic capacitor used on the active PFC circuit is Japanese from Matsushita (Panasonic), which is great. It is labeled at 85º C.
On the switching section this power supply uses another two SPW16N50C3 power MOSFET transistors, on the traditional two-transistor forward configuration. The specs for these transistors are published above.
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Figure 11: Switching transistors.
The primary is controlled by a FAN4800 active PFC/PWM controller combo installed on a small printed circuit board, a direct competitor to the very popular CM6800 integrated circuit.
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Figure 12: Active PFC/PWM controller.
The primary from ST-550P-AM is identical to ST-550P-AG’s. Let’s see now the secondary.
