A Look Inside

Look at what we found when we removed the casing. A Seasonic S12 II wearing a BITWIN suit!


As we are going to do in every review we will start the internals description from the transient filtering (or EMI) stage. Right behind the AC receptacle we find a small PCB housing the first part of the transient filter, with one X, four Y caps and one coil on it. The second part is located on the main PCB and its consisted of two coils, an MOV, one X and two Y caps. As you can see the transient filter has way more than the necessary components, which of course is a very good thing.


The Bridge rectifier is a GBU806 attached to a heatsink. Next, in the APFC stage we find two FDP18N50 MOSFETs and the boost diode. The main capacitor (105°C, 470 μF, 400V) that filters the APFC output is provided by Nippon Chemi-Con, a highly respectable manufacturer. Before the main cap there is an NTC (Negative Temperature Coefficient) thermistor that limits the in-rush current generated by the cap's sudden charge when power is initially applied to the PSU. Unfortunately there is no relay to bypass the thermistor when its job is done, meaning that a small percentage of efficiency is lost on it and the most significant is that while the PSU is operating the thermistor doesn't have the time to cool down to do its job properly again, when asked for it (e.g. in a sudden switch off - delayed switch on that will find the main cap completely discharged).
The main switchers are two FDP18N50 in push-pull topology. Behind the APFC capacitors there is a vertical daughter-board which holds the combo PFC/PWM controller, an Infineon ICE1CS02


The secondary stage is equipped with only two coils, meaning the presence of group regulation. The big one is for +12/5V and the smaller one for 3.3V. Three 30A50CT SBRs (Schottky Barrier Diodes) handle the +12V regulation, one 40U45CT the 5V rail and finally 3.3V are regulated by an STPS30L30C. All caps in the secondary stage are from Nipon Chemi-Con and rated at 105°C. The protections IC, anHY-510N, is located in a vertical daughter-board. It supports only Over Voltage and Under Voltage Protections (OVP and UVP) so there is no OCP (Over Current Protection). We also verified the lack of OCP by examining the rear (solder) side of the main PCB, where we didn't find any shunt resistor(s) in the secondary stage, near the area were the +12V wires are connected to the PCB. Also we must note here that the +12V wires are all jumpered together, so this fact along with the lack of OCP and shunt resistors prove that there is only one +12V rail and not two as the manufacturer claims.


Soldering quality is decent but only average compared to other Seasonic PSUs we looked at in the past. However these were X-series, the current top of the line of Seasonic's PSUs, so the comparison is pretty unfair. On the solder side of the main PCB there is also an SBR10U45, responsible for the 5VSB rectification.


The fan is provided by ADDA (AD1212MB-A70GL).