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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
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 12.063V | 11.907V | 1.29% | Pass |
| 5V | 5.024V | 4.898V | 2.51% | Pass |
| 3.3V | 3.324V | 3.134V | 5.72% | Fail |
| 5VSB | 5.076V | 5.040V | 0.71% | Pass |
Advanced Transient Response at 20% – 10ms
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 12.065V | 11.934V | 1.09% | Pass |
| 5V | 5.023V | 4.911V | 2.23% | Pass |
| 3.3V | 3.325V | 3.149V | 5.29% | Pass |
| 5VSB | 5.076V | 5.029V | 0.93% | Pass |
Advanced Transient Response at 20% – 1ms
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 12.066V | 11.953V | 0.94% | Pass |
| 5V | 5.023V | 4.904V | 2.37% | Pass |
| 3.3V | 3.325V | 3.140V | 5.56% | Fail |
| 5VSB | 5.076V | 5.043V | 0.65% | Pass |
Advanced Transient Response at 50% – 20ms
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 12.052V | 11.945V | 0.89% | Pass |
| 5V | 5.002V | 4.868V | 2.68% | Pass |
| 3.3V | 3.309V | 3.130V | 5.41% | Fail |
| 5VSB | 5.036V | 4.993V | 0.85% | Pass |
Advanced Transient Response at 50% – 10ms
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 12.054V | 11.948V | 0.88% | Pass |
| 5V | 5.001V | 4.886V | 2.30% | Pass |
| 3.3V | 3.309V | 3.126V | 5.53% | Fail |
| 5VSB | 5.036V | 4.993V | 0.85% | Pass |
Advanced Transient Response at 50% – 1ms
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 12.055V | 11.947V | 0.90% | Pass |
| 5V | 5.000V | 4.884V | 2.32% | Pass |
| 3.3V | 3.309V | 3.126V | 5.53% | Fail |
| 5VSB | 5.036V | 4.994V | 0.83% | Pass |
The deviation at 12V is at good levels since it remains close to 1%. On the minor rails the transient response is not so good though, especially at 3.3V.
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.
Besides the usual waveform steps, for a Focus platform, on the 12V rail, there is nothing more here to comment—all in all, good performance.
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.
| T1 (Power-on time) & T3 (PWR_OK delay) | ||
|---|---|---|
| Load | T1 | T3 |
| 20% | 92ms | 324ms |
| 100% | 85ms | 322ms |
The PWR_OK delay is out of the 100-150ms region, so the PSU does not support the alternative sleep mode, which will is recommended by the ATX spec. As we already mentioned in the prologue, though, there are no compatible mainboards available yet. What matters the most, for the moment, is for the Power-on time to be lower than 100ms, to avoid compatibility issues with picky mainboards, and the C750 achieves that.
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).
| Test | 12V | 5V | 3.3V | 5VSB | Pass/Fail |
| 10% Load | 9.8 mV | 6.2 mV | 5.4 mV | 5.5 mV | Pass |
| 20% Load | 13.4 mV | 6.3 mV | 5.7 mV | 6.0 mV | Pass |
| 30% Load | 15.8 mV | 7.0 mV | 6.2 mV | 6.5 mV | Pass |
| 40% Load | 17.9 mV | 7.1 mV | 6.9 mV | 6.7 mV | Pass |
| 50% Load | 13.8 mV | 7.6 mV | 6.9 mV | 6.5 mV | Pass |
| 60% Load | 12.2 mV | 7.8 mV | 7.1 mV | 6.9 mV | Pass |
| 70% Load | 12.2 mV | 8.5 mV | 7.6 mV | 7.3 mV | Pass |
| 80% Load | 12.7 mV | 9.2 mV | 13.6 mV | 8.4 mV | Pass |
| 90% Load | 14.6 mV | 10.1 mV | 14.6 mV | 9.1 mV | Pass |
| 100% Load | 22.7 mV | 11.8 mV | 15.4 mV | 9.2 mV | Pass |
| 110% Load | 26.5 mV | 12.6 mV | 15.5 mV | 10.3 mV | Pass |
| Crossload 1 | 14.4 mV | 12.2 mV | 14.3 mV | 7.3 mV | Pass |
| Crossload 2 | 21.7 mV | 9.0 mV | 8.2 mV | 8.5 mV | Pass |
Ripple suppression is good on all rails.
Ripple At Full Load
Ripple At 110% Load
Ripple At Cross-Load 1
Ripple At Cross-Load 2
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.
With the AVG EMI detector, some spurs are exceeding the limits. On the contrary, with the more accurate QP EMI detector, everything is fine.
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