Advanced Transient Response Tests

In these tests, we monitor the response of the PSU in two different scenarios. First, a transient load (11A at +12V, 5A at 5V, 6A at 3.3V, and 0.5A at 5VSB) is applied to the PSU for 50 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. In any case, 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 500W.





Although low capacity is a significant handicap in these tests, the PSU achieved a good performance overall. The +12V rail, the most important of all, registered a deviation of around 1% in both tests and only the 3.3V rail exceeded 4% deviation in the first test; nevertheless, its voltage remained above 3.2V.

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

Transient Response at 20% Load

Transient Response at 50% Load

Turn-On Transient Tests

In the next set of tests, we measure the response of the PSU in simpler scenarios of transient loads, during the power-on phase of the PSU. In the first test, we turn off the PSU, dial 2A of load at 5VSB and then switch on the PSU. In the second test, while the PSU is in standby mode, we dial the maximum load that +12V can handle and we start the PSU. 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 and then we switch on the PSU from the loader and we restore 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 for 5V is 5.5V).


All slopes ramped up smoothly and there were no noticeable voltage overshoots or spikes. Moreover, the rise time in all the tests was within the range that the ATX spec specifies (0.2-20ms). All in all, the PSU performed excellently here.