Transient Response Tests
Advanced Transient Response Tests
For details on our transient response testing, please click here.
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 have remained 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, an instant 100-percent load of CPU/GPUs, etc.). 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 500W.
Advanced Transient Response at 20 Percent
Advanced Transient Response at 50 Percent
In the first test, the deviation on the +12V rail was high, most likely because of the PWM-mode operation of the primary switches. However, in the second test, the deviation on the same rail dropped significantly, at the levels that we expect to see from a PSU with such high capacity. Finally, on the 5V and 5VSB rails, performance during these tests was good overall, while at 3.3V, we would like to see close to 3 percent deviations.
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 response of the PSU in simpler transient-load scenarios, during the PSU's power-on phase.
For the first measurement, we turned off the PSU, dialed in the maximum current the 5VSB could output and then switched the PSU back on. In the second test, we dialed the maximum load the +12V 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 the power or switched off the PSU by flipping its on/off switch), we dialed the maximum load the +12V rail could handle before switching on the PSU from the loader and restoring the power. The ATX specification states that recorded spikes on any rails should not exceed 10 percent of their nominal values (+10 percent for 12V is 13.2V, and 5.5V for 5V).
We noticed only two small spikes during the last two tests, which took place after the rails settled down. We remember seeing something similar in the past in Seasonic's high-end implementations. In this specific case, the spikes are way lower than the limits that the ATX spec sets, so they don't pose any threat to the components that the PSU will feed with power.