Let’s now take an in-depth look on the primary stage from BFG ES-800. For a better understanding, please read our Anatomy of Switching Power Supplies tutorial.

This power supply uses one GBU1510 rectifying bridge on its primary, supporting up to 15 A at 100º C if a heatsink is used (which is the case), so in theory you 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 itself. Of course we are only talking about this component and the real limit will depend on all other components from the power supply.

click to enlarge
Figure 9: Rectifying bridge.

Two SPW32N50C3 power MOSFETs are used on the active PFC circuit, each one capable of delivering up to 32 A at 25º C or 20 A at 100º C in continuous mode (see the difference temperature makes) or up to 96 A at 25º C in pulse mode. These transistors have a RDS(on) of 0.11 ohms. RDS(on) is the resistance of the transistor when it is turned on. We are starting to add this information as the lower the RDS(on) is, less power is wasted when the transistor is working, i.e. the higher efficiency will be, at least in theory.

click to enlarge
Figure 10: Active PFC transistors and active PFC diode.

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 capacitors with small capacitance are physically smaller than capacitors with bigger capacitances. BFG ES-800 uses one 560 µF x 450 V capacitor (the black one from Panasonic/Matsushita, labeled at 85º C) connected in parallel to one 180 µF x 450 V capacitor (the blue one from Hitachi, labeled at 105º C); this is equivalent of one 740 µF x 450 V capacitor.

As mentioned all capacitors used on this power supply are Japanese, which do not leak. It would be nice to see all capacitors labeled at 105º C, but as mentioned one of them is labeled at 85º C. All other capacitors used on ES-800 are labeled at 105º C.

On the switching section two STW25NM50B power MOSFET transistors are used on configuration called half-bridge series ressonant, which uses a big coil in series between the output of the transistors and the transformer. Each transistor supports up to 22 A at 25º C or 14 A at 100º C (see the difference temperature makes) or 88 A in pulse mode at 25º C, presenting an RDS(on) maximum of 0.140 ohms.

click to enlarge
Figure 11: Switching transistors.

Instead of using one PWM/PFC combo controller this power supply uses separated integrated circuits: an NCP1395 PWM controller and an NCP1653 PFC controller.

click to enlarge
Figure 12: PWM controller.

click to enlarge
Figure 13: PFC controller.

Let’s now take a look on the secondary from this power supply.