Let’s now take an in-depth look on the primary stage from TOP-1100P10. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.
This power supply uses one GBJ2506 rectifying bridge on its primary, capable of delivering up to 25 A at 100º C. This component is clearly overspec'ed. The reason why is that at 115 V this unit would be able to pull up to 2,875 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 2,300 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 12: Rectifying bridge.
The active PFC circuit uses two 35N60C3 power MOSFET transistors. Each one is capable of handling up to 103.8 A @ 25º C in pulse mode (which is the case) or up to 34.6 A @ 25º C or 21.9 A @ 100º C (see the difference temperature makes).
The active PFC circuit uses two 1,200 µF electrolytic capacitors connected in series, so this is equivalent as having a single 600 µF capacitor. The advantage of using two capacitors in series instead of just one is that the voltage will be divided between the two caps and thus the manufacturer can use capacitors with lower voltage ratings (in fact this is exactly what happens on this power supply: it uses two 200 V capacitors instead of just one 400 V component as other products). The capacitors used here are Taiwanese from Teapo and rated at 85º C.
On the switching section this power supply uses two other 35N60C3 transistors, on the traditional two-transistor forward configuration. The specs for these transistors are published above. They drive the two available transformers, which have their primaries connected in parallel. So even though this power supply has two transformers they share the same driving circuit.
As you can see on Figure 13, all main semiconductors from the primary side are installed on the same heatsink.
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Figure 13: Switching transistors, active PFC diode and switching transistors.
The primary is controlled by a CM6800 active PFC/PWM controller combo installed on a small printed circuit board.
