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 BFG.
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 50º 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 two GBU606 rectifying bridges on its primary stage, which can deliver up to 6 A (rated at 100º C) each so the total current the rectifying section of this power supply can handle is of 12 A. This is more than adequate rating for a 800 W power supply. The reason why is that at 115 V this unit would be able to pull up to 1,380 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 1,104 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 three power MOSFET transistors instead of just two like the vast majority of power supplies on the market (the only other power supplies we’ve see using three transistors instead of two were OCZ StealthXStream 600 W and Zalman ZM600-HP). The transistors used are 20N60C3, the same one used by several other power supplies we reviewed, which are capable of delivering up to 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: One of the rectifying bridges and active PFC transistors.
On the switching section other two 20N60C3 power MOSFET transistors in two-transistor forward configuration are used. Even though these transistors have the same specs from the ones used on the active PFC circuit, they use a bigger packaging (TO-247 vs. TO-220), improving heat dissipation.
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Figure 10: Active PFC diode, switching transistors and the second rectifying bridge.
This power supply uses a CM6800 integrated circuit on its primary, which is a very popular active PFC and PWM controller combo. It is located on a small printed circuit board shown on Figure 11.
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Figure 11: Active PFC and PWM combo controller.
