On this page we will take an in-depth look at the primary stage of Thermaltake Toughpower 800 W. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one LL25XB60 rectifying bridge in its primary, which can deliver up to 25 A at 113º C if a heatsink is used (which is the case) or up to 3.6 A at 25º C is a heatsink is not used. So in theory you 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 itself. Talk about overspecification! 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.

Two SPA20N60C3 power MOSFETs are used on the active PFC circuit, each one capable of delivering up to 20.7 A at 25º C or 13.1 A at 100º C in continuous mode (note the difference temperature makes) or up to 62.1 A at 25º C in pulse mode. These transistors present a maximum resistance of 190 mΩ when turned on, a characteristic called RDS(on). This number indicates the amount of power that is wasted, so the lower this number the better, as less power will be wasted thus increasing efficiency.

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Figure 10: Active PFC transistors and diodes.

This power supply uses two electrolytic capacitors to filter the output from the active PFC circuit. The use of more than one capacitor here has absolute nothing to do with the “quality” of the power supply, as laypersons may assume (including people without the proper background in electronics doing power supply reviews around the web). Instead of using one big capacitor, manufacturers may choose to use two or more smaller components that will give the same total capacitance, in order to better accommodate space on the printed circuit board, as two or more capacitors with small capacitance are physically smaller than one capacitor with the same total capacitance. Toughpower 800 W uses two 330 µF x 450 V capacitors in parallel; this is equivalent of one 660 µF x 450 V capacitor. These electrolytic capacitors are Japanese, from Hitachi and rated at 85º C.

Toughpower 800 W uses a two-transformer design with two separated switching transistors driving each one of them. Several power supplies use two transformers, but usually they are identical and both are used to generate the +12 V output. What is unique about Toughpower 800 W is that one of the transformers (the bigger one) is solely in charge of generating the +12 V output, while the other one (the smaller one) is in charge of generating the +5 V output, with the +3.3 V being generated from the +5 V output. This way we could say that Toughpower 800 W has basically one +12 V and one +5 V power supply inside. This was probably done to increase efficiency.

The +12 V power supply is driven by another two SPA20N60C3 power MOSFETs, while the +5 V power supply is driven by two 2SK3667 MOSFETs, which present a maximum current of 7.5 A at 25º C in continuous mode or 30 A at 25º C in pulse mode (unfortunately the manufacturer doesn’t say the maximum current at 100º C), with an RDS(on) of 750 mΩ, which is extremely high.

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Figure 11:  +5 V switching transistors and +12 V switching transistors.

The switching transistors are connected using a design called “LLC resonant,” also known as a series parallel resonant converter, using a technique called "soft switching" to reduce losses and thus improve efficiency.

The active PFC circuit is controlled by an NCP1653 integrated circuit and each one of the switch sections is controlled by an L6598D integrated circuit.

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Figure 12: PWM controller for the +12 V power supply (top) and for the +5 V power supply (down).

Now let’s take a look at the secondary of this power supply.