Seasonic TFX 350W PSU Review

1. Introduction2. Seasonic TFX 350W (Bundle & Cables)3. Seasonic TFX 350W (External)4. Seasonic TFX 350W (Internal)5. High Res Gallery6. Testing Methodology and Results7. Closing Thoughts8. 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
• Extech digital sound level meter
• 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
88W	3.75	3.35	4.02	5.02	4.21	12.09	0.60	5.03	0.12	-12.07
176W	7.52	3.34	8.03	5.01	8.51	12.08	1.22	5.03	0.25	-12.06
263W	11.26	3.34	12.02	5.01	12.76	12.08	1.86	5.03	0.37	-12.06
350W	15.02	3.34	16.01	5.00	16.98	12.03	2.51	5.03	0.50	-12.06

Seasonic TFX 350W	Maximum Load
	396W

Load regulation is great across the output range. We managed to get an extra 46 Watts from the power supply before it would switch off.

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 supply complied with the ATX standard.

AC Ripple (mV p-p)
DC Load	+3.3V	+5V	+12V	5VSB
88W	5	10	20	5
176W	5	10	35	10
263W	10	10	45	10
350W	10	10	55	10

Ripple suppression on the minor rails is stellar, although the +12V output peaks at 55mV at full load. This is a little higher than we would expect from a Seasonic design, even in this form factor. Still it is worth pointing out that this is well within rated tolerance specifications (less than 50%).

Efficiency (%)
88W	88.67
176W	91.88
263W	91.58
350W	89.93

Efficiency is very strong, peaking at close to 92 percent at 50 percent load. Efficiency drops to close to 90% at full load.

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 Corsair Power Supply we have taken it into our acoustics room environment and have set our Digital Sound Level Noise Decibel Meter Style 2 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 Refrigerator
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)
88W	28.0
176W	31.8
263W	34.2
350W	36.9

This unit incorporates the Seasonic ‘Smart & Silent Fan Control' system. At less than 40% load, or under 25c the fan is said to disable completely.

With such a small fan there is always a concern that noise could potentially be an issue, so we put it to the test.

At loads under 100 watts and depending on ambient temperature, we found the fan would disable completely or at worst spin very slowly. It was completely inaudible at this point.

Once the unit hit a 200 watt load, the fan would spin up and would become audible, although not particularly intrusive.

At over 250 Watts the fan would become more active and at over 300 watts noise could become a slight issue. That said, there is really is no realistic situation in which you should be running this power supply at a continuous 350 watts under load.

Obviously with smaller 80mm fans there are compromises we need to accept but we do feel Seasonic could have equipped this unit with a higher grade fan that could have been (almost) completely inaudible, even at full load.

Temperature (c)
	Intake	Exhaust
88W	35	38
176W	38	41
263W	43	47
350W	47	56

Internal temperatures rise to an 9c above ambient variable under full load, which considering the compressed physical layout, is certainly acceptable.

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