BFG LS-550 (New) Power Supply Review

Secondary Analysis

This power supply uses four Schottky rectifiers on its secondary.

The maximum theoretical current each 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. Just as an exercise, we can assume a typical duty cycle of 30%.

The +12 V output is produced by two 40CPQ060 Schottky rectifiers, each one with a maximum current limit of 40 A (20 A per diode at 120° C, 0.49 V voltage drop). This gives us a maximum theoretical current of 57 A or 686 W for the +12 V output.

The +5 V output is produced by one STPS60L45CW Schottky rectifier, capable of delivering up to 60 A (30 A per internal diode at 135° C, voltage drop of 0.50 V). This means the +5 V output has a maximum theoretical current of 43 A or 214 W.

The +3.3 V output is produced by another STPS60L45CW Schottky rectifier, giving us a maximum theoretical current of 43 A or 141 W for the +3.3 V output.

Figure 12: +3.3 V, +5 V and the two +12 V rectifiers.

The outputs are monitored by a PS223 integrated circuit, which supports the following protections: over current (OCP), under voltage (UVP), over voltage (OVP) and over temperature (OTP, not implemented on this power supply). Any other protection that this unit may have is implemented outside this integrated circuit.

Figure 13: Monitoring integrated circuit.

Most electrolytic capacitors from the secondary are also Japanese, from Chemi-Con, but some models are from Teapo (Taiwanese company).

In summary, even though LS-450 and LS-550 (New) are based on the same project, all main components were upgraded on LS-550. This is really nice to see, because some manufacturers when releasing a power supply with a higher wattage only replaces the secondary rectifiers, not upgrading the primary.