Advanced Transient Response Tests

In these tests, we monitor the response of the PSU 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 to the PSU for 200 ms while the latter is working at a 20% load state. In the second scenario, the PSU, while working at 50% load, is hit by the same transient load. In both tests, we measure the voltage drops that the transient load causes using our oscilloscope. The voltages should remain within the regulation limits defined by the ATX specification. We must stress here that the above tests are crucial since they simulate transient loads that a PSU is very likely to handle (e.g., booting a RAID array, an instant 100% load of CPU/VGAs, etc.). We call these tests "Advanced Transient Response Tests", and they are designed to be very tough to master, especially for PSUs with capacities lower than 500 W.





The unit's response to sudden transient loads definitely isn't amongst the best we have ever seen, since the deviations were close to the 2% region at +12V and 5V, while the 3.3V rail failed to keep its voltage inside the specified range during the second test. Only the 5VSB rail performed really well here, with close to a 1% deviation on both tests. We would ideally like to see a drop under 2% on the +12V rail because it is the most important rail of all, and the one that will be stressed highly by dynamic loads.


Below, you will find the oscilloscope screenshots that we took during Advanced Transient Response Testing.

Transient Response at 20% Load

Transient Response at 50% Load

Turn-On Transient Tests

We measure the response of the PSU in simpler scenarios of transient loads—during the power-on phase of the PSU—in the next set of tests. In the first test, we turn the PSU off, dial the maximum current that the 5VSB can output, and then switch on the PSU. In the second test, we dial the maximum load that +12V can handle and start the PSU while the PSU is in standby mode. In the last test, while the PSU is completely switched off (we cut off power or switch off the PSU's on/off switch), we dial the maximum load that 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% of their nominal values (e.g., +10% for 12V is 13.2V and 5.5V for 5V).


At 5VSB, we measured a tiny voltage overshoot, while the "standby to full 12V" test has the slope make a small dive at around 10V before continuing smoothly. Things don't look so good in the last test, though, since we noticed two spikes and an abnormal slope. Nevertheless, the aforementioned spikes are far below the corresponding upper limit, so there is nothing to worry about. All in all, the unit registered passable results in these tests.