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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	12.096V	11.816V	2.31%	Pass
5V	5.016V	4.863V	3.05%	Pass
3.3V	3.301V	3.103V	6.00%	Fail
5VSB	5.053V	4.986V	1.33%	Pass

Advanced Transient Response at 20% – 10ms

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Voltage	Before	After	Change	Pass/Fail
12V	12.095V	11.823V	2.25%	Pass
5V	5.015V	4.857V	3.15%	Pass
3.3V	3.300V	3.101V	6.03%	Fail
5VSB	5.054V	4.993V	1.21%	Pass

Advanced Transient Response at 20% – 1ms

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Voltage	Before	After	Change	Pass/Fail
12V	12.094V	11.835V	2.14%	Pass
5V	5.015V	4.859V	3.11%	Pass
3.3V	3.300V	3.101V	6.03%	Fail
5VSB	5.055V	4.981V	1.46%	Pass

Advanced Transient Response at 50% – 20ms

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Voltage	Before	After	Change	Pass/Fail
12V	12.048V	11.757V	2.42%	Pass
5V	5.007V	4.851V	3.12%	Pass
3.3V	3.292V	3.090V	6.14%	Fail
5VSB	5.018V	4.949V	1.38%	Pass

Advanced Transient Response at 50% – 10ms

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Voltage	Before	After	Change	Pass/Fail
12V	12.047V	11.780V	2.22%	Pass
5V	5.005V	4.842V	3.26%	Pass
3.3V	3.291V	3.084V	6.29%	Fail
5VSB	5.019V	4.954V	1.30%	Pass

Advanced Transient Response at 50% – 1ms

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Voltage	Before	After	Change	Pass/Fail
12V	12.047V	11.760V	2.38%	Pass
5V	5.005V	4.844V	3.22%	Pass
3.3V	3.291V	3.088V	6.17%	Fail
5VSB	5.020V	4.950V	1.39%	Pass

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Thermaltake Smart BM2 750W — (Image credit: Tom's Hardware)

Results 25-29: Transient Response

The 12V rail performs well compared to most offerings, but still, its voltage drops are notable. The 5V and 5VSB rails don't have a problem, but this is not the case for the 3.3V rail, which fails 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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Turn-On Transient Response Scope Shots

There are no problems at 5VSB, and if there weren't a small step at both 12V slopes, the corresponding waveforms would be ideal.

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%	32ms	130ms
100%	32ms	129ms

The PWR_OK delay is within the 100-150ms region, so the PSU does support the alternative sleep mode, which is 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	8.8 mV	18.0 mV	13.8 mV	7.6 mV	Pass
20% Load	9.4 mV	15.2 mV	13.7 mV	7.3 mV	Pass
30% Load	11.0 mV	12.7 mV	13.8 mV	8.6 mV	Pass
40% Load	12.7 mV	10.5 mV	14.6 mV	7.2 mV	Pass
50% Load	14.9 mV	9.8 mV	14.7 mV	8.4 mV	Pass
60% Load	16.8 mV	11.0 mV	15.9 mV	12.0 mV	Pass
70% Load	20.7 mV	13.4 mV	16.8 mV	13.0 mV	Pass
80% Load	28.3 mV	15.5 mV	18.8 mV	15.9 mV	Pass
90% Load	40.3 mV	15.9 mV	21.0 mV	18.4 mV	Pass
100% Load	52.6 mV	17.9 mV	24.0 mV	22.6 mV	Pass
110% Load	64.9 mV	20.4 mV	26.6 mV	23.4 mV	Pass
Crossload 1	10.9 mV	19.7 mV	17.9 mV	6.2 mV	Pass
Crossload 2	59.0 mV	14.5 mV	22.6 mV	15.8 mV	Pass

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Results 30-33: Ripple Suppression

We would like to see lower ripple at 12V, under full load, ideally below 40mV. Ripple suppression is satisfactory on the other rails.

Ripple At Full Load

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Ripple Full Load Scope Shots

Ripple At 110% Load

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Ripple 110% Load Scope Shots

Ripple At Cross-Load 1

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Ripple CL1 Load Scope Shots

Ripple At Cross-Load 2

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Ripple CL2 Load Scope Shots

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.