Let’s now take an in-depth look on the primary stage from CWT-750VH. 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.
The active PFC circuit from this power supply uses two power MOSFET transistors (20N60C3 – the same one used by several other power supplies we took a look). Each 20N60C3 can handle up 300 A @ 25º C each in pulse mode (which is the case) or 45 A @ 25º C or 20 A @ 110º C in continuous mode.
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Figure 9: Rectifying bridge and active PFC transistors.
On the switching section other two 20N60C3 power MOSFET transistors in two-transistor forward configuration are used. These are the same transitors used on Corsair TX750W but Thermaltake Toughpower 750 W uses a different set of transistors (IRFP460A), which has a lower current limit (80 A vs. 300 A in pulsating mode, both rated at 25º C). In other words, at least in theory the primary stage from the reviewed power supply can deliver more current (and thus power) to the secondary stage than Toughpower 750 W. The primary section of CWT-750VH is identical to TX750W’s.
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Figure 10: Switching transistors.
The primary is controlled by a CM6800G integrated circuit, which is a PWM/active PFC controller and is physically located on a small printed circuit board attached to the main board.
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Figure 11: Active PFC and PWM controller.
The electrolytic capacitor used on the active PFC circuit is Japanese from Hitachi, which is terrific. It is rated at 85º C (see Figure 11).
