Spire SP-ATX-350WT-PFC – 350W “Jewel” review

Primary side

The primary side of the SP-ATX-350WT-PFC starts with input bridge rectifier, the KBL406. This is one of those bridges which basically consist of four discrete diodes molded into a single plastic package. It is thick, limited to 4 A continuously (200 A surge) at 50 °C ambient and does not mount to a heatsink. Maximum voltage is 800 V, voltage drop 1.1 V per diode. You can also see spots for discrete diodes (rated up to 3A) instead of the rectifier. The PFC choke uses real iron core and copper winding, no cement or similar stuff.


As for the bulk capacitors, as the topology is old, two 200V capacitors in series are still used even though the voltage doubler is absent. They are Fhy MKX 470 μF/200 V for 85 °C only. They are garbage with true capacitance under 330 μF, the effective capacitance is then slightly over 150 μF. The switchers are the ordinary TO-220-packaged 13007 BJTs in half-bridge configuration, as could be expected. Controller is the antique AZ7500BP-E1 aka KA7500 god knows from who.


The primary heatsink is not paper-thin and it has some reasonable surface area. But the main transformer is quite short with EI-33 core only on top of that. So my estimate is still just about 280 watts before it goes bwoosh.

+5 V stand-by rail

The stand-by rail is uses ordinary self-oscillating two-transistor forward with BU3150AF (3 A/800 V at 150 °C, ICEO 20 μA at 750 V, tf 0.5 μs at IC 1 A, IB 0.5 A) NPN transistor in TO-220F as the main switcher. The critical cap is from Asia’X (a.k.a. Fuhjyyu) TNX series. This brand is not complete crap but it is very close. Don’t use this thing, just don’t, this kind of circuit is very bad thing which can toast your motherboard easily.


The transformer here is EEL-19 and the single-way Schottky rectification diode is 1N5822 (3/80 A at 40 V), in DO-201AD package. Output filtering consists of two more Asia’X caps of TMX series, 1000 μF/16 V and 470 μF/10 V. There is even a coil in this filter.

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