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Corsair CS850M 850W Power Supply Review

A Look Inside And Component Analysis

Our main tools for disassembling PSUs are a Thermaltronics soldering and rework station and a Hakko 808 desoldering gun.

Parts Description

Primary Side
Transient Filter4x Y caps, 2x X caps, 2x CM chokes
Inrush ProtectionNTC Thermistor & Relay
Bridge Rectifier(s)2x  GBU1508
APFC MOSFETs2x Vishay SIHG33N60E
APFC Boost Diode1x CREE C3D08060A
Hold-up Cap(s)2x Rubycon (400V, 390uF each; 780uF combined, 85 °C, USG)
Main Switchers2x Fairchild FCH104N60F
APFC ControllerChampion CM6500 & CM03X Green PFC controller
Switching ControllerChampion CM6901X
TopologyPrimary side: Half-Bridge & LLC Resonant Converter Secondary side: Synchronous Rectification & DC-DC converters
Secondary Side
+12V MOSFETs4x BV4K
5V & 3.3VDC-DC Converters: 4x AP0403GH FETs 1x Anpec APW7159 PWM Controller
Filtering CapacitorsElectrolytics: Teapo, CapXon (105°C) Polymers: Elite, CapXon
Supervisor ICSitronix ST9S429-PQ14
Fan ModelHong Hua HA1425L12F-Z (140 mm, 12 V, 0.22 A, 1800 RPM)
5VSB Circuit
Rectifying Diode1x PFC PFR30L45CT
Standby PWM ControllerPower Integrations TNY278PN

The original manufacturer of this PSU is Great Wall, the same OEM that builds Corsair's other CS units. The PCB is small and densely populated for an 850W PSU, but the platform is a modern design. In the primary side, an LLC resonant converter is utilized for higher efficiency, while on the secondary side, several FETs regulate the +12V rail as VRMs handle the minor rails. A strange mix of Taiwanese- and Chinese-made polymer and electrolytic capacitors filter the secondary side's rails. Thankfully most of the electrolytic caps are provided by Teapo, which has a pretty good reputation among non-Japanese manufacturers. We found only one CapXon cap in a low-stress area. These are considered low-quality, so we don’t like seeing them in any PSU. Finally, we found proof on the PCB that the exact same board is used across the CS family. This is common, especially in mainstream and mid-range PSU lines, as a cost-cutting measure.

The AC receptacle and the on/off switch are installed on a small PCB, which also holds the first part of the transient/EMI filter along with two Y caps and a single X cap. The second part of the transient filter is on the main PCB and includes two CM chokes, two Y caps and a single X cap. Unfortunately, we didn’t find a MOV (Metal Oxide Varistor), which we believe to be an essential component since it provides protection against power surges coming from the mains grid. We also spotted an NTC thermistor in the same area, which handles large inrush currents, along with a relay that cuts it off once the start-up phase finishes and the APFC caps are fully charged.

Two bridge rectifiers (model number GBU1508) fully rectify the AC voltage. Combined, they can handle up to 30A of current, making them overkill for this PSU.

Two Vishay SIHG33N60E FETs are used in the APFC converter, along with a single CREE C3D08060A boost diode. The bulk or smoothing caps are provide by Rubycon (400V, 390uF each or 780uF combined, 85 °C, USG series), so they are of good quality. However, we would like to see caps that are rated at up to 105 °C instead of 85 degrees. Many manufacturers go with high-temp caps in the APFC converter. But Corsair's engineers apparently decided to use Japanese caps rated for 85 °C instead of Taiwanese or Chinese caps able to withstand 105 °C. Faced with the same choice, we're pick the Japanese caps as well. In the APFC control section we find a Champion CM6500 along with a CM03X Green PFC controller, both installed on the solder side of the main PCB.

A pair of Fairchild FCH104N60F FETs are used as main switchers. The LLC resonant controller is a Champion CM6901X, which operates the main switchers at PWM mode under light loads and switches to FM mode at higher loads. The controller is installed on the solder side of the mainboard.

Four BV4K FETs are installed in the secondary heat sink; they're responsible for regulating the +12V rail. There is also a PFR30L45CT SBR (Schottky Barrier Diode) bolted to the same sink. It regulates the 5VSB rail with the help of a TNY278PN standby PWM controller.

Almost all filtering caps on the secondary side are provided by Teapo, a brand we consider reliable. There's only one CapXon electrolytic cap - good news since we wouldn't trust a PSU full of CapXon capacitors. Many polymer caps provided by CapXon and Elite are also used for ripple filtering. Those wouldn't be our top choices, but since they are polymers, don't believe they'll cause any problems. 

Both VRMs are housed on the same PCB and have a common PWM controller, an Anpec APW7159A. Each VRM uses two AP0403GH FETs to regulate its output.

At the front side of the modular board we find another mix of CapXon and Elite polymer caps. Again, we'd prefer Teapo, though those higher-end caps would have increased production cost, affecting the CS850M's price. Still, we cannot overemphasize that the quality of capacitors used in a PSU plays a key role in defining its reliability and performance over time. It makes a little more sense why Corsair gives its lower-end family a shorter warranty than the higher-quality models, right?

Sitronix's ST9S429-PQ14, a protections IC, is installed on the main PCB. It's a rebadged Unisonic Technologies S3515 without OTP (over-temperature protection) support, so OTP must, if it's present at all, be implemented another way. In fact, Corsair informed us that OTP is indeed present and it is implemented via the fan controller. In case the internal temperature reaches very high levels, it triggers one of the other protections of the supervisor IC, effectively shutting the PSU down.

Soldering quality is good, especially for this PSU's price category.

The HA1425L12F-Z cooling fan is provided by Hong Hua (140mm, 12V, 0.22A, 1800 RPM). It is a mainstream model with a sleeve bearing, which can provide quieter operation compared to a fan with the same specs and ball bearings. The fan profile is relaxed enough to keep rotational speeds low under normal conditions.