Corsair TX750W Power Supply Review

Primary Analysis

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 Corsair.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.

We also need to know under which temperature the component manufacturer measured the component maximum current (this piece of information is also found on the component databook). The higher the temperature, the lower current semiconductors can deliver. Currents given at temperatures lower than 50° C are no good, as temperatures below that don’t reflect the power supply real working conditions.

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, the wire gauge and even the width of the printed circuit board traces – 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 in its primary stage, which can deliver up to 15 A (rated at 100° C). This component is 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). Some other power supplies like OCZ StealthXStream 600 W and Zalman ZM600-HP use three transistors here instead of two. Each 20N60C3 can handle up 300 A @ 25° C each in pulse mode (which is the case) or 45 A @ 25° C or 20 A @ 110° C in continuous mode.

Figure 10: Rectifying bridge and active PFC transistors.

In the switching section, another two 20N60C3 power MOSFET transistors in two-transistor forward configuration are used. Here lies one of the main differences between Corsair TX750W and Thermaltake Toughpower 750 W: this model from Corsair uses transistors with far higher current limits, which is great (300 A vs. 80 A in pulsating mode, both rated at 25° C). In other words, at least in theory the primary stage can deliver more current (and thus power) to the secondary stage.

Figure 11: Switching transistors.

The primary is controlled by a CM6800 integrated circuit, which is a very popular active PFC and PWM controller combo. It is located on a small printed circuit board shown in Figure 12.

Figure 12: Active PFC and PWM combo controller.