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Transient Response Tests
Advanced Transient Response Tests
For details on our transient response testing, please click here.
Ιn these tests, we monitor the PE-750's response in two different scenarios. First, a transient load (10 A at +12V, 5 A at 5V, 5 A at 3.3V and 0.5 A at 5VSB) is applied for 200 ms while the PSU works at 20 percent load. In the second scenario, the PE-750 is hit by the same transient load while operating at 50 percent load. In both tests, we use our oscilloscope to measure the voltage drops caused by the transient load. The voltages should remain within the ATX specification's regulation limits.
These tests are crucial because they simulate the transient loads a PSU is likely to handle (such as booting a RAID array or an instant 100 percent load of CPU/GPUs). We call these tests "Advanced Transient Response Tests," and they are designed to be very tough to master, especially for a PSU with a capacity of less than 500 W.
Advanced Transient Response at 20 Percent
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 11.920V | 11.804V | 0.97% | Pass |
| 5V | 5.088V | 5.004V | 1.65% | Pass |
| 3.3V | 3.325V | 3.211V | 3.43% | Pass |
| 5VSB | 5.064V | 5.013V | 1.01% | Pass |
Advanced Transient Response at 50 Percent
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 11.889V | 11.798V | 0.77% | Pass |
| 5V | 5.062V | 4.972V | 1.78% | Pass |
| 3.3V | 3.296V | 3.195V | 3.06% | Pass |
| 5VSB | 5.029V | 4.960V | 1.37% | Pass |
The +12V rail performs well in these tests; it stays below 1% in both cases. The 5V and 5VSB rails also fare admirably.
Conversely, the 3.3V rail's performance isn't satisfactory, as its voltage dropped below 3.2 V during the second test. Then again, compared to the other SFX and SFX-L PSUs we've reviewed, the PE-750 doesn't look so bad since only the Great Wall platform used by Corsair's SF family achieves better results.
Here are the oscilloscope screenshots we took during Advanced Transient Response Testing:
Transient Response At 20 Percent Load
Transient Response At 50 Percent Load
Turn-On Transient Tests
In the next set of tests, we measure the PE-750's response in simpler transient load scenarios—during its power-on phase.
For the first measurement, we turn off the PSU, dial in the maximum current the 5VSB can output, and switch the PE-750 on. In the second test, we dial the maximum load the +12V rail can handle and start the PSU while it's in standby mode. In the last test, while the PE-750 is completely switched off (we cut the power or switch it off by flipping its on/off switch), we dial the maximum load the +12V rail can handle before switching the PSU back on from the loader and restoring power. The ATX specification states that recorded spikes on all rails should not exceed 10 percent of their nominal values (+10 percent for 12 V is 13.2 V, and 5.5 V for 5 V).
We have a small spike at 5VSB, which is nothing to worry about, and almost perfect waveforms in the other two tests. Overall, this is very good performance.
