Primary Analysis
Contents
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 Enermax.
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 two RS2005G rectifying bridges in parallel in its primary stage. As each bridge can deliver up to 20 A, the primary rectifying bridge of this power supply can deliver up to 40 A. This stage is amazingly overspec’ed: at 115 V this unit would be able to pull up to 4,600 W from the power grid; assuming 80% efficiency, the bridge would allow this unit to deliver up to 3,680 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.
Figure 11: Rectifying bridges used on this power supply.
No less than eight power MOSFET transistors are used on the primary stage of this power supply. Four 24N50 are used on the active PFC circuit, while four 2SK2607 are used on the switching section (9 A in continuous mode each at 25° C).
For a better understanding on the relationship between these transistors, we drew a simplified diagram of this section of Galaxy 1000 W power supply, see Figure 13.
Figure 12: Simplified diagram of this power supply showing the location of the eight MOSFET transistors.
As you can see in Figure 12 this power supply uses two transformers with separated switching sections and separated outputs. Two transistors drive each transformer. A single-transistor forward configuration is used, with the two transistors connected in parallel in order to double the maximum current each switcher can handle. Each 2SK2607 can drive up to 9 A in continuous mode or 27 A in pulse mode (which is the case, as the PWM circuit that controls the transistors generate a square wave to control them), both numbers at 25° C. Thus each switcher can handle up to 54 A – i.e., up to this current can be delivered to each transformer, so the total amount of current the primary can theoretically deliver to the two transformers is of 108 A – which is a gigantic current amount.
Figure 13: MOSFET transistors used on this power supply.
Figure 14: MOSFET transistors used on this power supply.
If you pay close attention on the pictures above you will see that Enermax put small ferrite beads on the terminals of all transistors. This procedure was repeated on all power rectifiers used on the secondary. This beads act like a filter, decreasing the noise that may be produced by the circuit.
The active PFC circuit is controlled by a UCC3817 integrated circuit located on a small printed circuit board shown in Figure 15.
Figure 15: Active PFC controller.
