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Transient Response Tests
For details on our transient response testing, please click here.
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 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 tough to master.
| Advanced Transient Response 20% | ||||
|---|---|---|---|---|
| Voltage | Before | After | Change | Pass/Fail |
| 12V | 12.136V | 11.975V | 1.33% | Pass |
| 5V | 5.036V | 4.951V | 1.69% | Pass |
| 3.3V | 3.365V | 3.236V | 3.83% | Pass |
| 5VSB | 5.029V | 4.978V | 1.01% | Pass |
| Advanced Transient Response 50% | ||||
|---|---|---|---|---|
| Voltage | Before | After | Change | Pass/Fail |
| 12V | 12.107V | 12.058V | 0.40% | Pass |
| 5V | 5.016V | 4.930V | 1.71% | Pass |
| 3.3V | 3.357V | 3.231V | 3.75% | Pass |
| 5VSB | 5.010V | 4.957V | 1.06% | Pass |
In the first test, the PWM operation of the main switchers causes a significant deviation on the +12V rail. However, in the second test, the corresponding deviation drops to normal levels for a high-end, 1200W PSU. In general, this power supply yields a decent performance. But it still lags behind most of the competition in this category.
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
We measure the PSU's response in simpler transient-load scenarios — during the power-on phase of the PSU — 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 it is 5.5V for 5V).
Our equipment catches a minor spike at 5VSB, which is nothing to worry about. During the Standby to Full 12V test, the slope is smooth enough. However, in the third test, we notice large ripples on the waveform before the rails settle down to the nominal voltage level.
