A Look Inside & Component Analysis

Before reading this page, we strongly suggest a look at this article, which will help you understand the internal components of a PSU better.


All new Gold and Platinum X series Seasonic PSUs are based on the fresh KM 3 platform. This new design uses a full-bridge topology with an LLC converter for increased efficiency on the primary side. The secondary side uses synchronous rectification with the +12V mosfets. The mosfets are installed on a vertical daughter-board instead of the main PCB, which is their mounting spot on the KM2 platform. The move of the +12V fets to a vertical daughter-board allowed for better cooling of the fets and, as such, a larger fanless operation range. Finally, the DC-DC converters that generate the minor rails are installed directly onto the modular PCB for decreased power losses. All in all, the new KM3 platform uses a sophisticated and modern design to provide the best possible performance. Seasonic's technicians must have had a really tough time upgrading the already excellent KM2 platform, but they, judging from the results we have seen so far, did an outstanding job.


Behind the AC receptacle, we come across a sealed PCB that holds a few of the transient filtering stage components - namely, four Y caps, a CM choke, and a single X cap. On the main PCB, we find the other transient filtering components: two pairs of X and Y caps, two CM chokes, and an MOV. We also spotted a thermistor that protects the unit from large inrush currents and an electromagnetic relay that isolates it from the circuit once the APFC caps are fully charged. In general, the transient filtering stage is perfect since it has more parts than the minimum that are required.


Two GBJ 1506s are the parallel bridge rectifiers, and they can easily handle the maximum power of this unit.


In the APFC converter, we find two Infineon IPP50R250CP fets and a CREE C3D06060 boost diode. The two parallel hold-up caps are provided by Nippon Chemi-Con (400 V; 270 μF each or 540 μF combined; 105°C; KMR series). The Corsair AX760, which is a rebadged X-760 unit, uses two 330 μF caps here.


This small PCB houses the PFC controller: an NPC1654 IC.


The full bridge topology utilizes four Infineon IPP50R399CP fets. An LLC resonant converter is also used to boost efficiency through loss-less switching of the main switchers.


The LLC resonant controller, a Champion CM6901 IC, along with all fets that rectify +12V, are installed on a vertical PCB in the secondary side. Two heatsinks cool the aforementioned fets down, and we found an attached thermistor that provides temperature data to the fan-control circuit on one of them. Some soldered Enesol polymer caps under one of the heatsinks filter the +12V rail. Also, several electrolytic Chemi-Con caps are used to some purpose; they all belong to the KZE series and are rated at 105°C.


The DC-DC converters are installed on the modular PCB, and their common PWM controller is an APW7159 IC. On each one, three Infineon BSC0906NS fets are used. At the front of the same PCB, many small Enesol polymer caps filter the DC outputs.


On a vertical daughter-board, located at the edge of the secondary side, resides a Weltrend WT7257V supervisor IC, and an AS393 dual-voltage comparator. This supervisor IC supports OCP for up to two +12V virtual rails, but only one exists in the X-750.


The standby PWM controller is an ICE2QR4765 IC.


Soldering quality is typically Seasonic, which means that it is very good, but we spotted some last minute touch ups (look closely at the forth of the above photographs).


The San Ace 120 cooling fan is provided by Sanyo Denki and is of high quality. It uses double ball-bearings, and its model number is 9S1212F404 (12 V, 0.19 A, 2.200 RPM, 70.6 CFM). This is the fan that Seasonic uses with all of their high-end models.