We were very curious to check what components were chosen for the power section of this power supply and also how they were set together, i.e. the design used. We were willing to see if the components could really deliver the power announced by Thermaltake.
From all the specs provided on the databook of each component, we are more interested on the maximum continuous current parameter, given in ampères or amps for short. To find the maximum theoretical power capacity of the component in watts we need just to use the formula P = V x I, where P is power in watts, V is the voltage in volts and I is the current in ampères.
Keep in mind that this doesn’t mean that the power supply will deliver the maximum current rated for each component as the maximum power the power supply can deliver depends on other components used – like the transformer, coils, the PCB layout and the wire gauge – not only on the specs of the main components we are going to analyze.
For a better understanding of what we are talking here, please read our Anatomy of Switching Power Supplies tutorial.
This power supply uses one GBJ1506 rectifying bridge on its primary stage, which can deliver up to 15 A (rated 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.
Four power MOSFET transistors are used on this power supply primary, two on the active PFC circuit and two on the switching section. On the active PFC circuit two SPW20N60C3 are used, see Figure 15. These transistors have a maximum rated continuous current of 13.1 A at 100º C each (62.1 A in pulse mode at 25º C).
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Figure 15: Rectifying bridge (on the left) and active PFC transistors (on the right) used on this power supply.
On the switching section two IRFP460A power MOSFET transistors in two-transistor forward switcher configuration are used, and each one has a maximum rated current of 80 A in pulse mode, which is the mode used, as the PWM circuit feeds these transistors with a square waveform. In continuous mode they can deliver up to 20 A @ 25º C or up to 13 A @ 100º C (see the difference temperature makes). As you may have noticed we are now publishing the temperature spec of each component, as this will play a major role on our analysis. As you can see, the higher the temperature, the lower current semiconductors can deliver. We will discuss more about this later.
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Figure 16: The two switching transistors. On the other side of this heatsink is the PFC diode.
For a better understanding on the relationship between these transistors, we drew a simplified diagram of this section of Toughpower 750 W power supply, see Figure 17.
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Figure 17: Simplified diagram of this power supply showing the location of its four MOSFET transistors.
This power supply uses a CM6800 integrated circuit, which is an active PFC and PWM controller combo. It is located on a small printed circuit board shown on Figure 18.
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Figure 18: Active PFC and PWM controller integrated circuit.
