Transient Response Tests
Advanced Transient Response Tests
In these tests, we monitored the response of the PSU in two different scenarios. First, a transient load (10A at +12V, 5A at 5V, 5A at 3.3V and 0.5A at 5VSB) was applied to the PSU for 200ms while the PSU was working at 20 percent load. In the second scenario, the PSU was hit by the same transient load while operating at 50 percent load. In both tests, we used 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, as they simulate the transient loads that a PSU is likely to handle (such as booting a RAID array or an instant 100 percent CPU/GPU load). We call these Advanced Transient Response Tests, and they are designed to be very tough to master.
For details on our transient response testing, please click here.
Advanced Transient Response 20%
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 12.020V | 11.897V | 1.02% | Pass |
| 5V | 4.987V | 4.895V | 1.84% | Pass |
| 3.3V | 3.324V | 3.216V | 3.25% | Pass |
| 5VSB | 4.957V | 4.882V | 1.51% | Pass |
Advanced Transient Response 50%
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 11.969V | 11.878V | 0.76% | Pass |
| 5V | 4.957V | 4.868V | 1.80% | Pass |
| 3.3V | 3.300V | 3.189V | 3.36% | Pass |
| 5VSB | 4.915V | 4.843V | 1.46% | Pass |
Our Advanced Transient Response tests showed that the voltage drops were under control on all rails. However, we would have liked to see smaller deviations on the +12V rail, which handles transient loads constantly inside a real system. The higher-than-usual voltage drops on the 5VSB rail are not serious, since the average deviation was within 1.5 percent.
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 measured the PSU's response during the PSU's power-on phase.
For the first measurement, we turned off the PSU, dialed in the maximum current the 5VSB can output and then switched on the PSU. In the second test, we dialed the maximum load the +12V rail could handle and started the PSU while it was in standby mode. In the last test, while the PSU was completely switched off (we cut off power or switched off the PSU by flipping its switch), we dialed the maximum load the +12V rail could handle before switching on the PSU 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 12V is 13.2V, and 5.5V for 5V).
We measured a really tiny voltage overshoot at 5VSB and two larger voltage overshoots, but everything was pretty smooth on the other two tests. All in all, the PSU performed well here.
