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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 PSU'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 XP1200M 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 | 12.297V | 12.170V | 1.03% | Pass |
| 5V | 4.955V | 4.853V | 2.06% | Pass |
| 3.3V | 3.301V | 3.150V | 4.57% | Pass |
| 5VSB | 4.936V | 4.871V | 1.32% | Pass |
Advanced Transient Response at 50 Percent
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 12.228V | 12.096V | 1.08% | Pass |
| 5V | 4.917V | 4.815V | 2.07% | Pass |
| 3.3V | 3.272V | 3.130V | 4.34% | Fail |
| 5VSB | 4.892V | 4.826V | 1.35% | Pass |
The transient response performance of the +12V rail looks fair. However, in this high-end category we are only satisfied with lower than 1% deviations, and the ideal scenario is close to 0.5% voltage drops. The 5V and 5VSB rails perform quite well, while the 3.3V rail registers bad performance with high voltage drops that lead to a failure in the second test.
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 PSU's response in simpler transient load scenarios—during its power-on phase.
For the first measurement, we turn off the XP1200M, dial in the maximum current the 5VSB rail can output and switch the PSU on. In the second test, we dial the maximum load the +12V can handle and start the PSU while it's in standby mode. In the last test, while the XP1200M is completely switched off (we cut the power or switch the PSU off by flipping its on/off switch), we dial in the maximum load the +12V rail can before switching the PSU 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).
The 5VSB rail performs fine, and in the second test the +12V rail's slope looks pretty good. The commendable performance doesn't continue through the last test, where the +12V rail's voltage makes several waves before it settles down to its nominal voltage.
