Seasonic Focus SGX 500W SFX-L Power Supply Review: Top Performance In A Small Package

Transient Response Tests, Ripple Measurements and EMC Pre-Compliance Testing

Advanced Transient Response Tests

For details about our transient response testing, please click here.

In the real world, power supplies are always working with loads that change. It's of immense importance, then, for the PSU to keep its rails within the ATX specification's defined ranges. The smaller the deviations, the more stable your PC will be with less stress applied to its components. 

We should note that the ATX spec requires capacitive loading during the transient rests, but in our methodology we also choose to apply a worst case scenario with no extra capacitance on the rails. 

Advanced Transient Response at 20% – 200ms

VoltageBeforeAfterChangePass/Fail
12V11.972V11.802V1.42%Pass
5V4.996V4.914V1.64%Pass
3.3V3.317V3.174V4.31%Pass
5VSB5.118V5.072V0.90%Pass

Advanced Transient Response at 20% – 20ms

VoltageBeforeAfterChangePass/Fail
12V11.973V11.777V1.64%Pass
5V4.996V4.897V1.98%Pass
3.3V3.318V3.145V5.21%Pass
5VSB5.118V5.071V0.92%Pass

Advanced Transient Response at 20% – 1ms

VoltageBeforeAfterChangePass/Fail
12V11.972V11.798V1.45%Pass
5V4.996V4.893V2.06%Pass
3.3V3.318V3.150V5.06%Pass
5VSB5.118V5.075V0.84%Pass

Advanced Transient Response at 50% – 200ms

VoltageBeforeAfterChangePass/Fail
12V11.971V11.856V0.96%Pass
5V4.992V4.907V1.70%Pass
3.3V3.315V3.165V4.52%Pass
5VSB5.092V5.042V0.98%Pass

Advanced Transient Response at 50% – 20ms

VoltageBeforeAfterChangePass/Fail
12V11.972V11.800V1.44%Pass
5V4.992V4.889V2.06%Pass
3.3V3.315V3.135V5.43%Fail
5VSB5.092V5.044V0.94%Pass

Advanced Transient Response at 50% – 1ms

VoltageBeforeAfterChangePass/Fail
12V11.972V11.802V1.42%Pass
5V4.992V4.886V2.12%Pass
3.3V3.315V3.140V5.28%Pass
5VSB5.092V5.044V0.94%Pass

The performance of all rails but the 3.3V one is good. We would like to see lower deviations at 3.3V, ideally lower than 3%, without the caps that the ATX spec requires.

Turn-On Transient Tests

In the next set of tests, we measure the PSU's response in simpler transient load scenarios—during its power-on phase. Ideally, we don't want to see any voltage overshoots or spikes since those put a lot of stress on the DC-DC converters of installed components.

 

The 5VSB rail has a smooth slope, while the +12V rail features a small wave, which is nothing to worry about though.

Ripple Measurements

Ripple represents the AC fluctuations (periodic) and noise (random) found in the PSU's DC rails. This phenomenon significantly decreases the capacitors' lifespan because it causes them to run hotter. A 10 degrees Celsius increase can cut into a cap's useful life by 50 percent. Ripple also plays an important role in overall system stability, especially when overclocking is involved.

The ripple limits, according to the ATX specification, are 120mV (+12V) and 50mV (5V, 3.3V, and 5VSB).

Test12V5V3.3V5VSBPass/Fail
10% Load11.8 mV9.2 mV14.2 mV9.8 mVPass
20% Load13.5 mV10.8 mV15.1 mV10.1 mVPass
30% Load12.5 mV11.9 mV15.7 mV10.4 mVPass
40% Load12.6 mV12.8 mV16.0 mV10.4 mVPass
50% Load13.4 mV14.7 mV16.8 mV10.7 mVPass
60% Load14.8 mV16.5 mV17.8 mV11.2 mVPass
70% Load15.7 mV17.7 mV19.1 mV11.6 mVPass
80% Load17.1 mV20.8 mV21.6 mV12.6 mVPass
90% Load17.8 mV22.7 mV23.4 mV12.8 mVPass
100% Load26.3 mV23.7 mV23.9 mV14.6 mVPass
110% Load27.4 mV24.7 mV24.8 mV15.6 mVPass
Crossload 122.0 mV21.9 mV23.2 mV10.2 mVPass
Crossload 224.8 mV14.5 mV17.7 mV13.4 mVPass

The ripple suppression is very good on all rails, despite the lack of in-line caps in the unit's modular cables.

Ripple At Full Load

Ripple At 110% Load

Ripple At Cross-Load 1

Ripple At Cross-Load 2

EMC Pre-Compliance Testing – Average & Peak EMI Detector Results

Electromagnetic Compatibility (EMC) is the ability of a device to operate properly in its environment without disrupting the proper operation of other close-by devices.

Electromagnetic Interference (EMI) stands for the electromagnetic energy a device emits, and it can cause problems in other close-by devices if too high. For example, it can be the cause of increased static noise in your headphones or/and speakers.

There is a high spur at close to 150KHz, which goes above the corresponding limit with the average EMI detector. In the rest frequency range, the conducted EMI emissions stay low.

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