Let’s now take an in-depth look on the primary stage from Commander 650 W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.
This power supply uses one GBJ1506 rectifying bridge on its primary, which support up to 15 A at 100º C. This component is clearly overspec'ed: at 115 V this unit would be able to pull up to 1,725 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 1,380 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.
For the active PFC circuit Commander 650 W uses two SPW20N60C3 power MOSFET transistors, each one capable of delivering up to 20.7 A at 25º C or 13.1 A at 100º C in continuous mode (see the difference temperature makes) or up to 62.1 A in pulse mode.
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Figure 10: Rectifying bridge and active PFC transistors.
The active PFC capacitor is Japanese from Hitachi and rated at 85º C. All other CWT-based units we’ve reviewed to date also use a Japanese capacitor here.
On the switching section two STW20NK50Z power MOSFETs are used on the traditional two-transistor forward configuration. Each transistor is capable of delivering up to 17 A at 25º C or 10.71 A at 100º C in continuous mode or up to 68 A at 25º C in pulse mode. These transistors are different from the 750 W CWT-based power supplies we’ve reviewed, which use SPW20N60C3 transistors here, which have a higher current limit.
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Figure 11: The two switching transistors.
The primary is controlled by the omnipresent CM6800 PWM/PFC controller combo.
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Figure 12: PWM/PFC controller.
Let’s now analyze the secondary section from Commander 650 W.
