Corsair AX850 PSU Review: Top Performer and Dead Silent

If you need the best 850W power supply and you don't have a restrictive budget, the AX850 should be among your top choices. It registers high performance in all areas: efficiency, load regulation, ripple suppression, transient response and, on top of that, it is dead silent as well. This unit is based on the Seasonic Prime Titanium platform, which is the best analog design today. With such great analogue platforms, someone could wonder why spend more on digital ones, where all major functions are controlled by micro-controllers instead of analogue ICs. As we see it, in the near future the AX860i will be probably replaced by the AX850, which easily meets its performance, although this is a bit of a paradox, a digital platform to get replaced by an analogue one.

We have already reviewed the AX1000, and we were impressed enough to provide it with an editor's choice award. The AX850 keeps the performance bar high as well, since it is also based on the top-notch Seasonic Prime Titanium platform. Corsair decided to cooperate again with Seasonic and this is good news in our opinion, since this manufacturer has some great designs to show.

With 80 PLUS Platinum and ETA-A+ efficiency certifications there is no doubt that the AX850 is highly efficient and the LAMBDA-A+ noise certification clearly depicts its quiet operation, even under tough conditions.

The higher the efficiency levels the lower the thermal loads, so the cooling fan has less work to do and can rotate at lower speeds. Large heat sinks can also help in this, with a recent example being the Rog Thor 1200W unit. Nonetheless, you still need high efficiency levels since if the heat sinks reach their limits, increased airflow will be needed to handle heat dissipation and keep the temperatures of the internals low. 

Specifications

Manufacturer (OEM)Seasonic
Max. DC Output850W
Efficiency80 PLUS Titanium, ETA-A+ (91-94%)
NoiseLAMBDA-A+ (15-20 dB[A])
Modular✓ (Fully)
Intel C6/C7 Power State Support
Operating Temperature (Continuous Full Load)0 - 50°C
Over Voltage Protection
Under Voltage Protection
Over Power Protection
Over Current (+12V) Protection
Over Temperature Protection
Short Circuit Protection
Surge Protection
Inrush Current Protection
Fan Failure ProtectionNo
No Load Operation
Cooling135mm Fluid Dynamic Bearing Fan (HA13525L12F-Z)
Semi-Passive Operation✓ (Selectable)
Dimensions (W x H x D)152 x 87 x 172mm
Weight2 kg (4.41 lb)
Form FactorATX12V v2.4, EPS 2.92
Warranty10 Years

Power Specifications

Rail3.3V5V12V5VSB-12V
Max. PowerAmps20207030.3
Watts100840153.6
Total Max. Power (W)850

Cables & Connectors

Modular Cables
DescriptionCable CountConnector Count (Total)GaugeIn Cable Capacitors
ATX connector 20+4 pin (610mm)1116-20AWGYes
4+4 pin EPS12V (650mm)2218AWGYes
6+2 pin PCIe (670mm+100mm) 4816-18AWGYes
SATA (460mm+110mm+110mm+110mm)41618AWGNo
4 pin Molex (550mm+100mm+100mm)2618AWGNo
FDD Adapter (110mm)1122AWGNo
AC Power Cord (1400mm)1114AWG-

There are two EPS and eight PCIe connectors, along with 16x SATA and six 4-pin Molex. Needless to say that they are more than enough for an 850W unit. The cables are quite long but the distance between the peripheral connectors is small at only 100-110mm. Ideally it should be 150mm. Finally, we would like to see 16AWG gauges on the EPS cables for lower voltage drops at high loads.

Component Analysis

We strongly encourage you to a look at our PSUs 101 article, which provides valuable information about PSUs and their operation, allowing you to better understand the components we're about to discuss.

General Data
Manufacturer (OEM)Seasonic
Platform ModelPrime
Primary Side
Transient Filter6x Y caps, 3x X caps, 2x CM chokes, 1x MOV
Inrush ProtectionNTC Thermistor & Relay
Bridge Rectifier(s)2x Vishay LVB2560 (600V, 25A @ 105°C)
APFC MOSFETS2x Infineon IPP60R099CP (650V, 19A @ 100°C, 0.099 Ohm)
APFC Boost Diode1x CREE C3D10060 (600V, 10A @ 153°C)
Hold-up Cap(s)2x Nippon Chemi-Con (400V, 680uF & 470uF or 1150uF combined, 2000h @ 105°C, KMR)
Main Switchers4x Infineon IPP50R140CP
(550V, 15A @ 100°C, 0.140 Ohm)
Drivers For Main Switchers2x Silicon Labs Si8230BD
APFC ControllerON Semiconductor NPC1654
Switching ControllerChampion CM6901
TopologyPrimary side: Full-Bridge & LLC Resonant Converter
Secondary side: Synchronous Rectification & DC-DC converters
Secondary Side
+12V MOSFETS4x Infineon BSC014N04LS (40V, 100A @ 100°C, 1.4 mOhm)
5V & 3.3VDC-DC Converters: 6x Infineon BSC0906NS
PWM Controller: APW7159
Filtering CapacitorsElectrolytics: Nippon Chemi-Con (105°C, W, KYB)
1x Chemi-Con (5VSB circuit, 5-6,000h @ 105°C, KZH)
Polymers: FPCAP, Nippon Chemi-Con
Supervisor ICWeltrend WT7527V (OVP, UVP, OCP, SCP, PG )
Fan ModelHong Hua HA13525L12F-Z (135mm, 12V, 0.22A, 1600 RPM, Fluid Dynamic Bearing)
5VSB Circuit
Buck ConverterLeadtrend LD7750R
Rectifiers STMicroelectronics STU6N65K3 (650V, 3A @ 100°C, 1.3mOhm), Infineon BSC0906NS (30V, 40A @ 100°C, 4.5mOhm)
-12V Circuit
Buck ConverterLite-On LSP5523 (3A max output current )

This is the platform used in the Seasonic Prime Titanium Ultra models, and it is considered among the best analog platforms in today's market. It uses top-quality parts including Infineon FETs, Vishay bridge rectifiers, Chemi-Con electrolytic caps and a large number of polymer caps, provided by FPCAP.

In the primary side a full-bridge topology is utilized along with an LLC resonant converter, while in the secondary side we meet a synchronous rectification scheme and a pair of DC-DC converters, which regulate the minor rails. Finally, the mid-speed cooling fan is made by Hong Hua and it uses a fluid dynamic bearing, which besides a long lifetime also provides silent operation. The highly-relaxed fan profile plays a notable part as well, in keeping the noise low.