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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	12.061V	11.876V	1.54%	Pass
5V	5.014V	4.916V	1.95%	Pass
3.3V	3.276V	3.165V	3.38%	Pass
5VSB	5.049V	4.986V	1.25%	Pass

Advanced Transient Response at 20% – 10ms

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Voltage	Before	After	Change	Pass/Fail
12V	12.060V	11.903V	1.30%	Pass
5V	5.014V	4.922V	1.83%	Pass
3.3V	3.276V	3.167V	3.32%	Pass
5VSB	5.049V	4.989V	1.19%	Pass

Advanced Transient Response at 20% – 1ms

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Voltage	Before	After	Change	Pass/Fail
12V	12.062V	11.911V	1.24%	Pass
5V	5.014V	4.915V	1.98%	Pass
3.3V	3.276V	3.170V	3.25%	Pass
5VSB	5.049V	4.986V	1.26%	Pass

Advanced Transient Response at 50% – 20ms

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Voltage	Before	After	Change	Pass/Fail
12V	12.027V	11.902V	1.04%	Pass
5V	5.007V	4.913V	1.88%	Pass
3.3V	3.267V	3.153V	3.50%	Pass
5VSB	5.108V	5.073V	0.68%	Pass

Advanced Transient Response at 50% – 10ms

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Voltage	Before	After	Change	Pass/Fail
12V	12.028V	11.909V	0.99%	Pass
5V	5.008V	4.912V	1.92%	Pass
3.3V	3.267V	3.152V	3.53%	Pass
5VSB	5.108V	5.068V	0.78%	Pass

Advanced Transient Response at 50% – 1ms

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Voltage	Before	After	Change	Pass/Fail
12V	12.029V	11.947V	0.68%	Pass
5V	5.007V	4.917V	1.79%	Pass
3.3V	3.267V	3.149V	3.61%	Pass
5VSB	5.108V	5.072V	0.70%	Pass

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Thermaltake Toughpower GF3 850W — (Image credit: Tom's Hardware)

Transient response is average at 12V but pretty tight on the other rails. Still, I want to see over 3.2V at 3.3V in all cases.

ATX 3.0 Transient Response Tests

The following table shows the load that we applied.

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Duty Cycle	Time for Power Excursion (Te)	Time Constant (Tc)	Power @ Te	Power @ Tc
5%	100μs	1900μs	1700W	780.0W
8%	1ms	11.5ms	1530W	762.7W
12.5%	10ms	70ms	1360W	749.3W
25%	100ms	300ms	1020W	785.2W

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The PSU successfully passed all ATX 3.0 transient response tests for units equipped with 12VHPWR connectors.

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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The turn-on transient response is good overall. We noticed a slight drop during the last test, which won't cause any issues.

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 150 ms and the PWR_OK delay (T3) from 100 to 150 ms, 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%	62ms	126ms
100%	63ms	126ms

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PSU Timing Charts

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	4.9 mV	8.4 mV	6.2 mV	5.0 mV	Pass
20% Load	5.6 mV	8.2 mV	6.1 mV	5.2 mV	Pass
30% Load	17.8 mV	7.5 mV	6.4 mV	6.6 mV	Pass
40% Load	14.3 mV	7.6 mV	6.5 mV	6.8 mV	Pass
50% Load	13.5 mV	8.0 mV	7.0 mV	5.8 mV	Pass
60% Load	12.8 mV	8.1 mV	7.3 mV	6.5 mV	Pass
70% Load	12.6 mV	10.1 mV	12.9 mV	7.0 mV	Pass
80% Load	12.4 mV	11.9 mV	14.4 mV	7.4 mV	Pass
90% Load	12.4 mV	9.7 mV	9.4 mV	8.0 mV	Pass
100% Load	19.0 mV	11.1 mV	10.8 mV	8.3 mV	Pass
110% Load	19.9 mV	11.4 mV	11.0 mV	9.0 mV	Pass
Crossload 1	13.6 mV	10.4 mV	8.9 mV	9.5 mV	Pass
Crossload 2	13.4 mV	12.6 mV	7.2 mV	10.1 mV	Pass
Crossload 3	6.0 mV	6.2 mV	10.5 mV	8.9 mV	Pass
Crossload 4	16.7 mV	9.4 mV	8.8 mV	10.5 mV	Pass

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Ripple suppression is great on all rails.

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.