Seventeam ST-420BKV 420 W Power Supply Review

Secondary Analysis

This power supply uses four power Schottky rectifiers on its secondary section: one SBL4060PT and three SBL4040PT, all of them capable of delivering up to 40 A @ 100° C (20 A per internal diode).

Here we can see that this power supply uses an old design. Current power supplies can deliver more current from the +12 V outputs, where the CPU and the video cards are connected to. On Seventeam ST-420BKV, however, the +5 V output is the one with the highest current limit, a typical scenario for six/seven years ago.

Since this power supply is based on the half-bridge design, calculating the maximum theoretical current for each output is easy: all we need to do is add the maximum current supported by each diode.

The +12 V output uses one SBL4040PT, so it can deliver up to 480 W. The maximum current this line can really deliver will depend on other components, especially the coil used.

The +5 V output uses two SBL4040PT in parallel, so it can deliver up to 80 A or 400 W. On more recent power supplies it is the +12 V output that has two rectifiers in parallel, not the +5 V output.

Usually the +3.3 V output on low-end power supplies based on half-bridge design is achieved by a 3.3 V voltage regulator connected to the +5 V output. This power supply from Seventeam, however, uses a better design, using an independent Schottky rectifier for producing its +3.3 V output.

The +3.3 V output is produced by the SBL4060PT, so it can deliver up to 132 W. Always keep in mind that the maximum current this line can really deliver will depend on other components, especially the coil.

Figure 10: Power rectifiers used on the secondary.

Figure 11: Power rectifiers used on the secondary.

Even though the +5 V line and the +3.3 V line have separated rectifiers, they share the same transformer output. So the maximum current both lines can deliver will depend a lot on the transformer.

On Figure 12 you can see a thermal sensor connected to the secondary heatsink, which controls the fan speed according to the power supply temperature.

Figure 12: Thermal sensor found on the secondary heatsink.

The capacitors of the voltage doubler circuit are rated at 85° C and from Toshin Kogyo (TK), a Japanese vendor that sells rebranded Taiwanese caps from OST, and all other capacitors are Taiwanese, from CapXon (all rated 105° C).