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

Advanced Transient Response Tests

For details about our transient response testing, 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 additional capacitance on the rails.

Advanced Transient Response at 20% – 20ms

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Voltage	Before	After	Change	Pass/Fail
12V	12.069V	11.906V	1.35%	Pass
5V	5.026V	4.944V	1.63%	Pass
3.3V	3.307V	3.176V	3.96%	Pass
5VSB	5.002V	4.946V	1.12%	Pass

Advanced Transient Response at 20% – 10ms

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Voltage	Before	After	Change	Pass/Fail
12V	12.066V	11.827V	1.98%	Pass
5V	5.026V	4.942V	1.67%	Pass
3.3V	3.306V	3.172V	4.05%	Pass
5VSB	5.003V	4.946V	1.14%	Pass

Advanced Transient Response at 20% – 1ms

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Voltage	Before	After	Change	Pass/Fail
12V	12.064V	11.844V	1.82%	Pass
5V	5.025V	4.944V	1.61%	Pass
3.3V	3.306V	3.180V	3.81%	Pass
5VSB	5.002V	4.941V	1.22%	Pass

Advanced Transient Response at 50% – 20ms

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Voltage	Before	After	Change	Pass/Fail
12V	12.029V	11.893V	1.13%	Pass
5V	5.016V	4.942V	1.48%	Pass
3.3V	3.297V	3.160V	4.16%	Pass
5VSB	4.982V	4.941V	0.82%	Pass

Advanced Transient Response at 50% – 10ms

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Voltage	Before	After	Change	Pass/Fail
12V	12.027V	11.896V	1.09%	Pass
5V	5.016V	4.943V	1.46%	Pass
3.3V	3.297V	3.156V	4.28%	Pass
5VSB	4.982V	4.941V	0.82%	Pass

Advanced Transient Response at 50% – 1ms

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Voltage	Before	After	Change	Pass/Fail
12V	12.026V	11.949V	0.64%	Pass
5V	5.015V	4.928V	1.73%	Pass
3.3V	3.297V	3.158V	4.22%	Pass
5VSB	4.982V	4.930V	1.04%	Pass

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(Image credit: Tom's Hardware)

Results 25-29: Transient Response

The transient response at +12V with 20% load registers more than 1% deviation because the PSU operates in PWM mode, With 50% load it much better, since the switching mode changes to FM.

The 5V and 5VSB rails have good transient response, but this is not the case for 3.3V, which drops its voltage below 3.2V, in all tests.

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.

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(Image credit: Tom's Hardware)

Turn-On Transient Response Scope Shots

There is only a small voltage overshoot at 5VSB in these tests, which is nothing to worry about.

Power Supply Timing Tests

There are several signals generated by the power supply, which need to be within specified, by the ATX spec, ranges. If they are not, there can be compatibility issues with other system parts, especially mainboards. From year 2020, the PSU's Power-on time (T1) has to be lower than 150ms and the PWR_OK delay (T3) from 100 to 150ms, to be compatible with the Alternative Sleep Mode.

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PSU Timings Table
T1 (Power-on time) & T3 (PWR_OK delay)
Load	T1	T3
20%	52ms	140ms
100%	52ms	142ms

The PWR_OK delay is within the 100-150ms region. This means that the PSU supports the alternative sleep mode. It might not look so important now, since there are not compatible mainboards, yet. Still, it is nice to have a future-proof power supply.

Ripple Measurements

Ripple represent 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-degree Celsius increase can cut into a cap's useful life by 50%. 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).

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Test	12V	5V	3.3V	5VSB	Pass/Fail
10% Load	5.9 mV	5.3 mV	8.8 mV	3.7 mV	Pass
20% Load	15.8 mV	5.1 mV	8.9 mV	3.4 mV	Pass
30% Load	9.7 mV	8.1 mV	16.4 mV	5.5 mV	Pass
40% Load	9.0 mV	7.1 mV	15.2 mV	5.0 mV	Pass
50% Load	9.4 mV	6.9 mV	12.4 mV	4.9 mV	Pass
60% Load	10.0 mV	7.4 mV	12.9 mV	5.7 mV	Pass
70% Load	11.1 mV	10.0 mV	20.9 mV	7.7 mV	Pass
80% Load	11.4 mV	9.9 mV	18.6 mV	7.9 mV	Pass
90% Load	11.8 mV	10.3 mV	18.2 mV	8.1 mV	Pass
100% Load	14.7 mV	8.6 mV	14.2 mV	7.4 mV	Pass
110% Load	15.5 mV	9.3 mV	14.5 mV	7.8 mV	Pass
Crossload 1	14.4 mV	7.3 mV	11.5 mV	4.9 mV	Pass
Crossload 2	14.2 mV	8.0 mV	12.0 mV	7.2 mV	Pass

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(Image credit: Tom's Hardware)

Results 30-33: Ripple Suppression

The ripple suppression is excellent.

Ripple At Full Load

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(Image credit: Tom's Hardware)

Ripple Full Load Scope Shots

Ripple At 110% Load

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(Image credit: Tom's Hardware)

Ripple 110% Load Scope Shots

Ripple At Cross-Load 1

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(Image credit: Tom's Hardware)

Ripple CL1 Load Scope Shots

Ripple At Cross-Load 2

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(Image credit: Tom's Hardware)

EMC Pre-Compliance Testing – Average & Quasi-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 nearby devices.

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