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Review: Corsair AX1200i Digital ATX Power Supply

by Tarinder Sandhu on 6 August 2012, 09:30 4.5

Tags: Corsair

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A peek inside the beast

The second major improvement of the AX1200i rests with how Corsair goes about delivering clean, consistent power at all times. Though bearing similarities with the architecture employed in the non-I version - we believe both to be manufactured on behalf of Corsair by Flextronics - the all-new AX1200i adds what the firm calls digitally-controlled power.

Most PSUs use a series of analogue components to mete out the necessary voltage and ripple regulation and efficiency, with better supplies able to keep closer to the ideal - meaning perfect voltage under load and near-perfect suppression of the AC input voltage - than cheaper ones, as this is literally what you're paying for once capacity has been decided.

AX1200i replaces some of these parts with a digital signal processor (DSP) whose job is the same, that is, to regulate the voltage and ripple, ensuring it's as close to perfect as possible. Corsair claims that AX1200i's DSP, by actively measuring a glut of data and using a feedback system, on-the-fly, is able to keep DC 12V output regulation to +/- 1.5 per cent, to better compensate for any sudden DC drops with immediate rectification, and suppress noisome ripple to just one-third mandated by the ATX spec.

In particular, the DSP controls the power factor correction (PFC), which itself is important in synching up incoming AC voltage and the resulting current load - you want the current to be manipulated into a nice sinusoidal waveform, matching the voltage's, and the closer the match, the higher the PFC. Corsair claims a PFC of 0.99. Note, however, that traditional PFCs offer the same kind of correction factory (0.99). Bear in mind that all PFCs add to inefficiency to some degree, as they represent an extra step the PSU has to go through to align waveforms.

Drilling down some, the chunky 'box' by the AC inlet contains the goodies that do some of the EMI/transient filtering - the job here is clean up the AC voltage before being passed on to the AC/DC rectifiers, and so forth. We can just about glimpse the blue-headed Y-type caps under the AC receptacle

We know that both iterations of the AX1200 supply uses a couple of hold-up capacitors from Panasonic - slap-bang in the middle - and Corsair also continues with providing the minor-rail voltage from the 12V's, meaning it's a DC-to-DC PSU architecture. You can spy the fan-control board on the near side, too.

Aiming for better efficiency and voltage regulation by using a DSP also has the positive by-product of reducing the total number of components on a PCB. The AX1200i's is busy, sure, but not packed to the gills for a supply of this wattage. Soldering is above average and the unit's heft and internal quality leave a positive impression.

The 140mm fan is also identical to the AX1200's. Super-high-efficiency PSUs produce little by way of heat, converting well over 90 per cent of the incoming AC power to the DC used by the PC. And considering 80 PLUS Platinum-rated supplies need to be efficient across a wide range, there's little need to use a fan at low wattages.

Following on from the no-fan-at-low-loads approach on recent Corsair PSUs, this beastie's fan is factory-programmed not to turn on until the required load tips past 40 per cent. Simple maths tells us that, if true, the unit is practically silent at DC load below 500W, which is more than enough to power relatively high-end systems running at full chat.

Amps/watts and voltage
Rail amps
Maximum rating
Maximum rating continuous
1,204.8W @ 50°C ambient

The modern PSU trend is to shunt as much power down the 12V rail as possible. The AX1200i is specified with an impressive 100.4A, leading to a total of 1,204.8W. The number's a little strange but follows the AX1200's. Corsair's using some meaty wiring and insulation to ensure that a potential 100A doesn't cause problems.

Remember how we spoke about the DSP-imbued AX1200i being able to spit out data to the PC via the Corsair LINK interface? We first connected the AX1200i to our Core i7-3700K PC and installed a wattage-guzzling GeForce GTX 590 for fun.

We have the PC under complete duress and the system's drawing around 450W from the mains. Do be aware that the efficiency isn't reported absolutely correctly. Faced with the eight-threaded chip subject to Prime95 torture and the GTX 590 up against FurMark, the AX1200i's fan remains switched off at all times. The PSU temperature is very good, also, and though we have mentioned the supply is designed with a single 12V rail in mind, it can be auto-switched to multi-rail and specific tripping points, should you so wish.

Using a Chroma load-tester enables granular wattages to be set. We measured the fan-activation point at around 475W, though it can be manually set in the LINK software.

Pre-benchmark summary

Using the established AX1200 PSU as a base and improving upon it with higher efficiency, better overall regulation and hardware-reporting features, the AX1200i, set to retail for £260, or about £50 more than the incumbent AX1200, begs to be tested. Let's now see how it performs.