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Switching Power Supplies A to Z
Switching Power Supplies A to Z, by Sanjaya Maniktala (Newnes), starting at $94.17
Home » Power
BFG 800 W Power Supply Review
Author: Gabriel Torres
Type: Reviews Last Updated: February 16, 2008
Page: 5 of 10
Real-time pricing for XFX P1-750B-NLG9.
XFX P1750BNLG9 Pro Series XXX Edition ATX Semi-Modular Power Supply 750W 80 Plus Silver 135mm Fan Active PFC
TigerDirect: $129.99 Newegg: $129.99
CompUSA: $129.99

Secondary Analysis
Hardware Secrets Silver Award

This power supply uses eight Schottky rectifiers on its secondary.



The +12 V output is produced by four 48CTQ060 Schottky rectifiers connected in parallel, which can deliver up to 40 A each (20 A per internal diode, measured at 111º C). The maximum theoretical current the +12 V line can deliver is given by the formula I / (1 - D), where D is the duty cycle used and I is the maximum current supported by the rectifying diode (which in this case is made by four 20 A diodes in parallel). Just as an exercise, we can assume a typical duty cycle of 30%. This would give us a maximum theoretical current of 114 A or 1,371 W for the +12 V output. The maximum current this line can really deliver will depend on other components, in particular the coil used. As you can see this stage is highly overspec'ed.

The +5 V output is produced by two STPS30L45CT Schottky rectifiers connected in parallel, which support up to 30 A (15 A per internal diode, measured at 135º C) each. The maximum theoretical current the +5 V line can deliver is given by the formula I / (1 - D), where D is the duty cycle used and I is the maximum current supported by the rectifying diode (which in this case is made by two 15 A diodes in parallel). Just as an exercise, we can assume a typical duty cycle of 30%. This would give us a maximum theoretical current of 43 A or 214 W for the +5 V output. The maximum current this line can really deliver will depend on other components, in particular the coil used.

The +3.3 V output is produced by two other STPS30L45CT Schottky rectifiers connected in parallel, which support up to 30 A (15 A per internal diode, measured at 135º C) each. Following the same math, this output would be able to deliver up to 43 A or 141 W, in theory.

Even though this power supply has a separated rectifier for the +3.3 V output, this rectifier is connected to the same transformer output as the +5 V line, so the maximum current +5 V and +3.3 V can pull together is limited by the transformer.

BFG 800 W
click to enlarge
Figure 12: Four of the eight Schottky rectifiers used on the secondary. The diode on the left is used by the +5VSB output.

BFG 800 W
click to enlarge
Figure 13: The other four rectifiers.

On this power supply the thermal sensor is installed inside the +12 V coil. The purpose of this sensor is to control the fan speed according to the power supply internal temperature.

On this power supply the active PFC capacitor is rated at 85º C, while the electrolytic capacitors from the secondary are rated at 105º C and are manufactured by CapXon, a Taiwanese company.

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