Transient Response Tests
Advanced Transient Response Tests
For details on our transient response testing, please click here.
In these tests, we monitor 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) is applied to the PSU for 200ms while the PSU is working at 20-percent load. In the second scenario, the PSU 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 since they simulate 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 below 500W.
20 Percent
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 12.108V | 12.010V | 0.81% | Pass |
| 5V | 5.059V | 4.944V | 2.27% | Pass |
| 3.3V | 3.314V | 3.188V | 3.80% | Pass |
| 5VSB | 5.083V | 5.047V | 0.71% | Pass |
50 Percent
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 12.081V | 12.006V | 0.62% | Pass |
| 5V | 5.035V | 4.929V | 2.11% | Pass |
| 3.3V | 3.294V | 3.172V | 3.70% | Pass |
| 5VSB | 5.048V | 4.998V | 0.99% | Pass |
On the +12V rail, the deviations were low in both tests. But we would like to see better results on the 5V and 3.3V rails. Finally, at 5VSB the results were good enough since the average deviation was within one percent.
Below 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
We measure the response of the PSU in simpler scenarios of transient load—during the power-on phase of the PSU—in the next set of tests.
For the first measurement, we turn the PSU off, dial the maximum current the 5VSB can output and then switch on the PSU. In the second test, we dial the maximum load +12V can handle and start the PSU while it's in standby mode. In the last test, while the PSU is completely switched off (we cut off the power or switch the PSU off by flipping the on/off switch), we dial the maximum load the +12V rail can handle 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% for 12V is 13.2V and 5.5V for 5V).
Pretty smooth slopes on all three turn-on tests. We noticed only some minor spikes after the voltage settle down to +12V; these are nothing to worry about.
