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Transient Response Tests
Advanced Transient Response Tests
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, 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 below 500 W.
| Advanced Transient Response 20% | ||||
|---|---|---|---|---|
| Voltage | Before | After | Change | Pass/Fail |
| 12V | 12.097V | 11.856V | 1.97% | Pass |
| 5V | 5.002V | 4.860V | 2.84% | Pass |
| 3.3V | 3.341V | 3.189V | 4.55% | Pass |
| 5VSB | 5.003V | 4.968V | 0.70% | Pass |
| Advanced Transient Response 50% | ||||
|---|---|---|---|---|
| Voltage | Before | After | Change | Pass/Fail |
| 12V | 12.020V | 11.873V | 1.22% | Pass |
| 5V | 4.970V | 4.829V | 2.84% | Pass |
| 3.3V | 3.307V | 3.171V | 4.11% | Pass |
| 5VSB | 9.958V | 4.912V | 0.93% | Pass |
SilverStone manages to pass these tests. However, we would like to see lower deviations on the 3.3V rail, where the voltage dropped below 3.2V once the transient load was applied. We don't want to see such low readings there; we'd be satisfied with anything above 3.2V, in fact.
The deviation at +12V was higher than the second test with an overall higher load. Normally it's the other way around. This has to do with the primary switchers' PWM operation at lower loads. Under a normal load, the resonant controller makes them operate in FM mode.
Advanced Transient Response Comparison Charts
Below are the oscilloscope screenshots we took during Advanced Transient Response Testing.
Transient Response At 20% Load - Oscilloscope Screenshots
Transient Response At 50% Load - Oscilloscope Screenshots
Turn-On Transient Tests
We measure the response of the PSU in simpler transient load scenarios -- during the power-on phase -- in the next set of tests.
For the first measurement, we turn the PSU off, 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 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 power. The ATX specification states 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).
During the first test, the slope is absolutely perfect. In in the remaining two tests, the slope ramps up smoothly, but before the voltage settles down, there is a small dive. That's nothing to worry about; overall performance in these tests is good.
