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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 it works 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 because they simulate the 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 tough to master.
Advanced Transient Response at 20 Percent
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 12.232V | 12.122V | 0.90% | Pass |
| 5V | 5.089V | 5.012V | 1.51% | Pass |
| 3.3V | 3.353V | 3.194V | 4.74% | Pass |
| 5VSB | 5.004V | 4.978V | 0.52% | Pass |
Advanced Transient Response at 50 Percent
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 12.172V | 12.061V | 0.91% | Pass |
| 5V | 5.071V | 4.990V | 1.60% | Pass |
| 3.3V | 3.322V | 3.170V | 4.58% | Pass |
| 5VSB | 4.970V | 4.929V | 0.82% | Pass |
The 5V and 5VSB rails do pretty well in our tests, but we would have liked to see lower deviations at +12V, which managed to stay within one percent in both tests. Things didn’t go well for the 3.3V rail, though. It exceeded 4.5 percent deviation on both tests and took last place in the corresponding comparison chart.
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
In the next set of tests, we measure the response of the PSU in simpler scenarios of transient load: during the power-on phase of the PSU.
For the first measurement, we turn off the PSU, dial in 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 its on/off switch), we dial the maximum load the +12V rail can handle before switching the PSU on from the loader and restoring the power. The ATX specifications state 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).
