Topower PowerBird 900 W Power Supply Review

Secondary Analysis

As mentioned, this power supply has two transformers, both driven by the same switching transistors. The first transformer, labeled T3 on the printed circuit board (and T122F on its top) is in charge of the +3.3 V and the +12 V outputs, while the second transformer, labeled T4 on the printed circuit board (and T121F on its top) is in charge of the +5 V and +12 V outputs. So while +3.3 V and +5 V outputs are produced by different transformers, the +12 V is produced by the two transformers, each one connected to a different transistor (see below).

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 rectification is done with a synchronous design. On synchronous design the diodes are replaced by MOSFET transistors. On this power supply the direct rectification is done by two IRFB3206 MOSFETs (210 A at 25° C or 150 A at 100° C each in continuous mode or 840 A at 25° C in pulse mode each) – each one connected to a different transformer – while the “freewheeling” portion is done by three KCQ60A06 Schottky rectifiers (60 A at 69° C each) connected in parallel. For our math we need to consider the portion with the lower current limit, which is probably the rectification portion. From our understanding the transformers and thus the transistors work out of phase (i.e., switching at opposite times), and thus they are not turned on at the same time. So we have a maximum theoretical current of 214 A (150 A / 0.70) at 100° C, which equals to 2,571 W. That is what we call going overboard with overspec’ing!

The +5 V output is produced by two STPS60L45CW Schottky rectifiers connected in parallel, each one capable of delivering up to 60 A (30 A per internal diode at 135° C). This gives us a maximum theoretical current of 86 A or 429 W for the +5 V output.

The +3.3 V output is produced by one STPS60L30CW, which is capable of delivering up to 60 A (30 A per internal diode at 130° C). This gives us a maximum theoretical current of 43 A or 141 W for the +3.3 V output.

Figure 13: +5VSB diode, +12 V transistor, +12 V rectifiers and +5 V rectifier (remaining components are on the other side of the heatsink).

Instead of using a monitoring integrated circuit, this power supply implements a discrete solution, using comparator integrated circuits (LM393 and LM339).

Figure 14: Monitoring circuit.

Electrolytic capacitors from the secondary are manufactured by Teapo and Hermei and labeled at 105° C.