Corsair AX750 Power Supply Review

1. Introduction2. The Corsair AX750 Power Supply3. The Corsair AX750 Power Supply (Internal)4. Testing Methodology and Results5. Closing Thoughts6. View All Pages

Additional technical assistance: Peter McFarland and Jeremy Price.

Correctly testing power supplies is a complex procedure and KitGuru have configured a test bench which can deliver up to a 2,000 watt DC load. Due to public requests we have changed our temperature settings recently – previously we rated with ambient temperatures at 25C, we have increased ambient temperatures by 10c (to 35c) in our environment to greater reflect warmer internal chassis conditions.

We use combinations of the following hardware:
• SunMoon SM-268
• CSI3710A Programmable DC load (+3.3V and +5V outputs)
• CSI3711A Programmable DC load (+12V1, +12V2, +12V3, and +12V4)
• Extech Power Analyzer
• Extech MultiMaster MM570 digital multimeter
• SkyTronic DSL 2 Digital Sound Level Meter (6-130dBa)
• Digital oscilloscope (20M S/s with 12 Bit ADC)
• Variable Autotransformer, 1.4 KVA

DC Output Load Regulation
Combined DC Load	+3.3V		+5V		+12V		+5VSB		-12V
	A	V	A	V	A	V	A	V	A	V
155W	1.5	3.34	1.5	5.04	11	12.15	0.50	5.03	0.20	-12.13
300W	3	3.34	3	5.04	22	12.13	1.00	5.02	0.30	-12.12
445W	4	3.33	4	5.03	33	12.12	1.50	5.01	0.50	-12.11
605W	5.5	3.33	5.5	5.02	45	12.11	2.00	5.01	0.60	-12.10
751W	7	3.32	7	5.00	56	12.08	3.00	5.00	0.80	-12.09

These results are excllent with primary and secondary outputs all remaining with 1% of their target values.

Corsair AX750W	Maximum Load
	892W

We managed to get 892W out of the unit before it shut down. As with the other AX power supplies we experienced absolutely no issues with the overcircuit protection circuity.

Next we want to try Cross Loading. This basically means loads which are not balanced. If a PC for instance needs 500W on the +12V outputs but something like 30W via the combined 3.3V and +5V outputs then the voltage regulation can fluctuate badly.

Cross Load Testing	+3.3V		+5V		+12V		-12V		+5VSB
	A	V	A	V	A	V	A	V	A	V
733W	1.0	3.33	1.0	5.02	60.0	12.04	0.2	-12.09	0.50	5.03
153W	15.0	3.32	15.0	5.01	2.0	12.01	0.2	-12.12	0.50	5.01

The Corsair AX750 experienced no issues with our crossloading tests and even with a 60A load on the 12V output it kept everything close to a reference set of parameters.

We then used an oscilloscope to measure AC ripple and noise present on the DC outputs. We set the oscilloscope time base to check for AC ripple at both high and low ends of the spectrum. ATX12V V2.2 specification for DC output ripple and noise is defined in the ATX 12V power supply design guide.

ATX12V Ver 2.2 Noise/Ripple Tolerance
Output	Ripple (mV p-p)
+3.3V	50
+5V	50
+12V1	120
+12V2	120
-12V	120
+5VSB	50

Obviously when measuring AC noise and ripple on the DC outputs the cleaner (less recorded) means we have a better end result. We measured this AC signal amplitude to see how closely the Corsair unit complied with the ATX standard.

AC Ripple (mV p-p)
DC Load	+3.3V	+5V	+12V	5VSB
155W	5	5	10	5
300W	5	5	10	5
445W	5	10	15	10
605W	10	15	15	10
751W	10	15	20	15

The AX750 ripple results are class leading and are just as impressive as the AX850 unit.

Efficiency (%)
155W	90.08
300W	90.41
445W	92.32
605W	91.55
751W	90.21

Efficiency, as we had hoped, is stellar, reading over 90% throughout the range, peaking at over 92% between 360-450W. This makes the 750W our new class leader in this category and certainly into the upper echelons of efficiency performance on the market. Gold Certification requires 87% efficiency rating at 100% load … the AX750 rates over 3% higher with our equipment.

We take the issue of noise very seriously at KitGuru and this is why we have built a special home brew system as a reference point when we test noise levels of various components. Why do this? Well this means we can eliminate secondary noise pollution in the test room and concentrate on components we are testing. It also brings us slightly closer to industry standards, such as DIN 45635.

Today to test the Power Supply we have taken it into our acoustics room environment and have set our SkyTronic DSL 2 Digital Sound Level Meter (6-130dBa) one meter away from the unit. We have no other fans running so we can effectively measure just the noise from the unit itself.

As this can be a little confusing for people, here are various dBa ratings in with real world situations to help describe the various levels.

KitGuru noise guide
10dBA – Normal Breathing/Rustling Leaves
20-25dBA – Whisper
30dBA – High Quality Computer fan
40dBA – A Bubbling Brook, or a Refridgerator
50dBA – Normal Conversation
60dBA – Laughter
70dBA – Vacuum Cleaner or Hairdryer
80dBA – City Traffic or a Garbage Disposal
90dBA – Motorcycle or Lawnmower
100dBA – MP3 Player at maximum output
110dBA – Orchestra
120dBA – Front row rock concert/Jet Engine
130dBA – Threshold of Pain
140dBA – Military Jet takeoff/Gunshot (close range)
160dBA – Instant Perforation of eardrum

Noise (dBA)
155W	/
300W	17.8
445W	23.5
605W	30.3
751W	37.9

A fantastic set of results, and it is only when around 90% load that the PSU fan becomes noticeably audible. A normal system running with a few case fans will mask this noise. The San Ace 120 is a great fan and the noise with this testing is comparible to the AX850 unit. We changed our meter for this review (we used the Digital Sound Level Noise Decibel Meter Style 2 before) so results are much in line.

Temperature (c)
	Intake	Exhaust
155W	35	37
300W	35	38
445W	40	44
605W	43	49
751W	45	52

The 120mm San Ace fan ensures the internal temperatures are relatively low, with the unit peaking at 7c + over ambient at full load.

Maximum load	Efficiency
892W	86.0

For those interested, we measured efficiency when stressing the unit to breaking point. 86% efficiency at almost 900W is a very good result indeed.

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