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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	12.019V	11.714V	2.54%	Pass
5V	5.149V	4.983V	3.23%	Pass
3.3V	3.342V	3.131V	6.32%	Fail
5VSB	5.076V	5.008V	1.33%	Pass

Advanced Transient Response at 20% – 10ms

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Voltage	Before	After	Change	Pass/Fail
12V	12.019V	11.530V	4.07%	Pass
5V	5.150V	4.938V	4.11%	Pass
3.3V	3.342V	3.134V	6.23%	Fail
5VSB	5.076V	4.980V	1.89%	Pass

Advanced Transient Response at 20% – 1ms

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Voltage	Before	After	Change	Pass/Fail
12V	12.019V	11.577V	3.67%	Pass
5V	5.150V	4.940V	4.09%	Pass
3.3V	3.342V	3.138V	6.09%	Pass
5VSB	5.076V	4.989V	1.72%	Pass

Advanced Transient Response at 50% – 20ms

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Voltage	Before	After	Change	Pass/Fail
12V	11.989V	11.732V	2.14%	Pass
5V	5.144V	4.971V	3.36%	Pass
3.3V	3.336V	3.118V	6.55%	Fail
5VSB	5.062V	5.004V	1.15%	Pass

Advanced Transient Response at 50% – 10ms

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Voltage	Before	After	Change	Pass/Fail
12V	11.989V	11.741V	2.07%	Pass
5V	5.144V	4.970V	3.37%	Pass
3.3V	3.336V	3.117V	6.56%	Fail
5VSB	5.062V	4.991V	1.41%	Pass

Advanced Transient Response at 50% – 1ms

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Voltage	Before	After	Change	Pass/Fail
12V	11.989V	11.709V	2.34%	Pass
5V	5.145V	4.928V	4.22%	Pass
3.3V	3.336V	3.117V	6.56%	Fail
5VSB	5.062V	4.947V	2.27%	Pass

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Asus TUF-Gaming 450 — (Image credit: Tom's Hardware)

Transient response is mediocre on all rails, but 5VSB, where it doesn't matter so much.

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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We didn't notice the colossal voltage drop in the "PSU OFF To Full 12V" test that we found in the 550W model. Nevertheless, there is a voltage step in this test, which can create compatibility issues with some mainboards.

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%	38ms	114ms
100%	38ms	113ms

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The PWR_OK delay is within the 100-150ms region, so the PSU supports the alternative sleep mode 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. 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	28.3 mV	7.8 mV	7.4 mV	10.2 mV	Pass
20% Load	26.6 mV	9.4 mV	8.7 mV	13.7 mV	Pass
30% Load	21.2 mV	10.4 mV	9.1 mV	15.2 mV	Pass
40% Load	18.5 mV	11.2 mV	10.1 mV	16.0 mV	Pass
50% Load	19.6 mV	12.2 mV	11.4 mV	20.6 mV	Pass
60% Load	15.8 mV	12.7 mV	11.3 mV	19.0 mV	Pass
70% Load	14.7 mV	13.0 mV	12.2 mV	20.9 mV	Pass
80% Load	16.6 mV	14.5 mV	14.6 mV	19.2 mV	Pass
90% Load	18.6 mV	15.4 mV	15.6 mV	21.5 mV	Pass
100% Load	30.9 mV	17.0 mV	17.9 mV	27.5 mV	Pass
110% Load	32.0 mV	18.1 mV	17.8 mV	27.2 mV	Pass
Crossload 1	29.4 mV	13.5 mV	14.2 mV	11.9 mV	Pass
Crossload 2	22.7 mV	13.4 mV	9.1 mV	10.1 mV	Pass
Crossload 3	26.1 mV	9.1 mV	15.3 mV	9.2 mV	Pass
Crossload 4	29.6 mV	15.9 mV	14.3 mV	18.0 mV	Pass

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Ripple suppression is good on all major rails. The 5VSB needs a better filtering cap, which is also the case for the 550W unit.

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 4

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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.