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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, 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 additional capacitance on the rails.

Advanced Transient Response at 20% – 20ms

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Voltage	Before	After	Change	Pass/Fail
12V	12.103V	11.896V	1.71%	Pass
5V	5.033V	4.862V	3.40%	Pass
3.3V	3.316V	3.180V	4.10%	Pass
5VSB	5.000V	4.928V	1.44%	Pass

Advanced Transient Response at 20% – 10ms

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Voltage	Before	After	Change	Pass/Fail
12V	12.104V	11.869V	1.94%	Pass
5V	5.033V	4.880V	3.04%	Pass
3.3V	3.316V	3.180V	4.10%	Pass
5VSB	5.000V	4.940V	1.20%	Pass

Advanced Transient Response at 20% – 1ms

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Voltage	Before	After	Change	Pass/Fail
12V	12.103V	11.921V	1.50%	Pass
5V	5.032V	4.875V	3.12%	Pass
3.3V	3.316V	3.176V	4.22%	Pass
5VSB	5.000V	4.952V	0.96%	Pass

Advanced Transient Response at 50% – 20ms

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Voltage	Before	After	Change	Pass/Fail
12V	12.038V	11.828V	1.74%	Pass
5V	4.995V	4.830V	3.30%	Pass
3.3V	3.291V	3.153V	4.19%	Pass
5VSB	4.962V	4.918V	0.89%	Pass

Advanced Transient Response at 50% – 10ms

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Voltage	Before	After	Change	Pass/Fail
12V	12.038V	11.823V	1.79%	Pass
5V	4.994V	4.848V	2.92%	Pass
3.3V	3.291V	3.154V	4.16%	Pass
5VSB	4.962V	4.905V	1.15%	Pass

Advanced Transient Response at 50% – 1ms

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Voltage	Before	After	Change	Pass/Fail
12V	12.038V	11.858V	1.50%	Pass
5V	4.995V	4.817V	3.56%	Pass
3.3V	3.291V	3.136V	4.71%	Fail
5VSB	4.962V	4.896V	1.33%	Pass

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Corsair CX550F — (Image credit: Tom's Hardware)

Transient response is good at 12V for a low capacity PSU, decent at 5VSB, and average at 5V. At 3.3V, the deviation is not among the highest we have seen in this category. Still, voltage drops were high, and as a result, the PSU failed in one test.

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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Everything is fine here with no notable voltage overshoots or spikes.

Power Supply Timing Tests

There are several signals generated by the power supply need to be within ranges specified by the ATX spec. If they are not, there can be compatibility issues with other system parts, especially mainboards. Since the 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%	38ms	124ms
100%	37ms	125ms

The PWR_OK delay is within the 100-150ms region, so the PSU supports the alternative low power modes recommended by the ATX spec.

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. For example, a 10-degree Celsius increase can reduce a cap's useful life by 50%. Ripple also plays a vital 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	14.1 mV	8.0 mV	7.5 mV	11.2 mV	Pass
20% Load	13.7 mV	7.4 mV	10.4 mV	9.1 mV	Pass
30% Load	13.5 mV	8.1 mV	8.5 mV	10.9 mV	Pass
40% Load	14.4 mV	8.2 mV	9.0 mV	10.4 mV	Pass
50% Load	18.3 mV	8.8 mV	9.4 mV	12.2 mV	Pass
60% Load	18.4 mV	9.5 mV	10.4 mV	13.9 mV	Pass
70% Load	22.8 mV	9.2 mV	12.4 mV	13.7 mV	Pass
80% Load	24.3 mV	10.4 mV	14.2 mV	16.8 mV	Pass
90% Load	29.7 mV	11.0 mV	14.2 mV	17.4 mV	Pass
100% Load	45.8 mV	14.0 mV	16.8 mV	21.1 mV	Pass
110% Load	52.3 mV	14.4 mV	17.1 mV	21.7 mV	Pass
Crossload 1	19.0 mV	10.9 mV	17.5 mV	7.4 mV	Pass
Crossload 2	44.2 mV	11.7 mV	12.7 mV	15.7 mV	Pass

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Ripple suppression is good on the minor rails. The 12V rail doesn't perform so well here. We would like to see below 40mV in the worst-case scenario.

Ripple At Full Load

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Ripple At 110% Load

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Ripple At Cross-Load 1

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Ripple At Cross-Load 2

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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 cause increased static noise in your headphones or/and speakers.

΅We use TekBox's EMCview to conduct our EMC pre-compliance testing.