Disassembly
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The input filtering consists of two X-Capacitors, two Coils, four Y-Capacitors (two of which are on the AC Receptacle), and one MOV. This is easily enough components for the job. The two Primary capacitors are 680µF parts supplied by the Nichicon – a well respected Japanese company. This unit uses a single transistor forward design, so there is only one switching transistor. The part used is a Fairchild FQA11N90 MOSFET rated at 11.4A at 25°C and 7.2A at 100°C. The Swithcer is driven by an ST Micro UC3843B PWM controller.
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The secondary side capacitors are made by Teapo, with the exception of one which is used on the 5vsb, which is supplied by Nippon Chemi-Con. It’s located on the other side of the heat sink, and, in most power supplies, is the first capacitor to fail, which is probably why Dell opted to use a Japanese part. Unfortunately, one of the Teapo capacitors is positioned right next to a hot load resistor, which has discoloured the PCB. Placing capacitors next to hot components is never a good idea, especially if they are from Taiwanese brands like the Teapo parts used here.
The 12V rail uses two different Shcottky rectifiers – a 20A STPS20S100CT and a 10A Fairchild FYP1010DN, so the 12V rail should be good for up to 30A, assuming the other components are up to the job. The 5V rail uses two Fairchild MBRP3045N Schottky rectifiers rated at 30A, so it should be capable of up to 60A. The 3.3V rail uses an interesting design. It uses its own MBRP3045N Rectifier with a 5V transformer output, but uses a MOSFET to regulate it down to 3.3V. This is much like using DC-DC conversion from the 5V rail, except that it has its own current source, rather than having to steal it from the 5V output. This also explains how low the ripple was as the type of DC-DC conversion circuit used here generally doesn’t produce very much ripple, but are quite inefficient compared to the circuits used on higher end power supplies. The secondary controller IC was covered in glue, so I couldn’t read the part number. There are two visible shunts for the 12V rails, so it’s a fair assumption that it supports OCP on at least two 12V rails.
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The soldering quality is excellent, as is usually the case with Chicony built power supplies. Note how the PCB is slightly darkened near the middle of the above right picture. Soldered here is the resistor I was referring to earlier.
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The fan is a sleeve bearing part made by ADDA. This model has speed, noise and airflow ratings of 3010RPM, 34.4dBA, and 38.6CFM respectively. It is temperature controlled and was very quiet until the overload test. Unfortunately, however, there was no lubricant in the bearings, so the fan may not last a very long time. The heat sinks are very thick, and are easily good enough for a 300W unit. The primary heat sink is very short, but with only one transistor to cool, it doesn’t need to be very big.
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