Let’s now take an in-depth look on the primary stage from BFG LS-450. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.
This power supply uses one GBU806 rectifying bridge on its primary, which can deliver up to 8 A at 100º C. This component is clearly overspec’ed: at 115 V this unit would be able to pull up to 920 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 736 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.
On the active PFC circuit one SPW32N50C3 power MOSFET transistors is used, capable of delivering up to 32 A at 25º C or 20 A at 100º C (see the difference temperature makes) in continuous mode or 96 A in pulse mode at 25º C. This is the first time we’ve seen a power supply using only one transistor on the active PFC circuit.
The active PFC capacitor is Japanese from Chemi-Con and labeled at 105º C. This is good for two reasons. Usually manufacturers use 85º C capacitors here, so it is good to see a manufacturer using a capacitor with a higher temperature rating. Secondly, Japanese capacitors don’t suffer from leakage problems.
On the switching section two STP12NM50 power MOSFET transistors are used on the traditional two-transistor forward configuration. Each one is capable of delivering up to 12 A at 25º C or 7.5 A at 100º C (see the difference temperature makes) in continuous mode or 48 A in pulse mode at 25º C.
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Figure 10: One of the switching transistors, active PFC diode and active PFC transistor.
The primary is controlled by a CM6806A PFC/PWM combo controller.
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Figure 11: PFC/PWM combo controller.
Let’s now take a look on the secondary from this power supply.
