On this page we will take an in-depth look at the primary stage of BFG LS-450. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.
This power supply uses one GBU806 rectifying bridge in its primary, which can deliver up to 8 A at 100° 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.
On the active PFC circuit one SPW32N50C3 power MOSFET transistor is used, capable of delivering up to 32 A at 25° C or 20 A at 100° C in continuous mode (note the difference temperature makes) or 96 A in pulse mode at 25° 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 105° C. This is good for two reasons. Usually manufacturers use 85° 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.
In 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 25° C or 7.5 A at 100° C in continuous mode (note the difference temperature makes) or 48 A in pulse mode at 25° C.
The primary is controlled by a CM6806A PFC/PWM combo controller.
Now let’s take a look at the secondary of this power supply.