Seasonic Focus GX-850 V4 ATX v3.1 PSU Review

Part Analysis

General Data
Manufacturer (OEM) Seasonic
PCB Type Double-Sided
Primary Side
Transient Filter 4x Y caps, 2x X caps, 2x CM chokes, 1x MOV
Inrush Protection 1x NTC Thermistor MF72 5D-20L (5 ohm) & Relay
Bridge Rectifier(s)
2x GBU1508 (800V, 15A @ 40°C)
APFC MOSFETs
2x Alpha & Omega AOB160A60L (600V, 15A @ 100°C, Rds(on): 0.16Ohm)
APFC Boost Diode
1x Infineon IDK08G65C5 (650V, 8A @ 145°C)
Bulk Cap(s)
1x Nippon Chemi-con (400V, 680uF, 2,000h @ 105°C, KMR)
Main Switchers
4x Alpha & Omega AOB280A60C (600V, 9A @ 100°C, Rds(on): 0.28Ohm)
Resonant Controller
Champion CU6901VPA
APFC Controller
Champion CM6500UNX
Topology
Primary side: APFC, Full-Bridge & LLC converter
Secondary side: Synchronous Rectification & DC-DC converters
Secondary Side
+12V MOSFETs 4x Nexperia PSMN1R4-40YLD (40V, 214A @ 100°C, Rds(on): 1.4mOhm)
5V & 3.3V DC-DC Converters:  6x Nexperia PSMN4R0_30YLD   (30V, 95A @ 100°C, Rds(on): 4mOhm)
PWM Controller(s): Anpec APW7159C
Filtering Capacitors Electrolytic:
3x Nichicon (2-5,000h @ 105°C, HD),
1x Nippon Chemi-Con (1-5,000h @ 105°C, KZE),
5x Rubycon (3-6,000h @ 105°C, YXG)
2x Rubycon (6-10,000h @ 105°C, ZLH)
Polymer: 5x Nippon Chemi-Con,
18x FPCAP
Supervisor IC Weltrend WT7527RA (OVP, UVP, OCP, SCP, PG)
Fan Controller Nuvoton M031FB0AE
Fan Model Hong Hua HA13525H12F-Z (135mm, 12V, 0.50A, Fluid Dynamic Bearing Fan)
5VSB
Rectifier
DK DK5V45R10S (45v, 10mOhm)
Standby PWM Controller
Excelliance MOS EM8569C

Despite the small PCB, plenty of space is available, and the distance between parts is large to allow for enhanced airflow. The large vertical PCBs on the sides allow for an uncrowded PCB. One holds the APFC converter and the main FETs, while the other daughterboard holds both DC-DC converters that generate the minor rails. Seasonic used surface-mounting FETs with tiny heatsinks since the PCB also cools them. This is an interesting design to have a vertical board holding a significant part of the PSU’s primary side. Speaking of the primary side, a full-bridge topology is used for enhanced reliability and increased efficiency. On the secondary side, the 12V FETs are installed on the top PCB side, so they come in direct contact with the fan’s airflow.

Overall, the soldering quality is good, and all the parts that Seasonic used are of high quality, including Nichicon, Rubycon, Chemi-Con, and FPCAP capacitors, along with Alpha & Omega and Nexperia FETs. Moreover, the cooling fan is by Hong Hua, which has been among the most popular fan manufacturers in the PSU market in recent years, and for good reason.

The fan is digitally controlled by an MCU, which is optimal, but you still have to program it accordingly to have a good fan speed profile. Moreover, I would like to see MCUs controlling other parts of the PSU as well.

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