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Advanced Transient Response Tests
For details on our transient response testing, please click here.
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 “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.
In all of the tests, we use an oscilloscope to measure the voltage drops caused by the transient load. The voltages should remain within the ATX specification's regulation limits.
We should note that the ATX spec requires for capacitive loading during the transient rests, but in our methodology we chose to apply the worst case scenario with no extra capacitance on the rails.
Advanced Transient Response at 20 Percent – 200ms
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 12.089V | 11.917V | 1.42% | Pass |
| 5V | 5.027V | 4.844V | 3.64% | Pass |
| 3.3V | 3.380V | 3.175V | 6.07% | Pass |
| 5VSB | 5.061V | 4.998V | 1.24% | Pass |
Advanced Transient Response at 20 Percent – 20ms
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 12.087V | 11.839V | 2.05% | Pass |
| 5V | 5.034V | 4.834V | 3.97% | Pass |
| 3.3V | 3.384V | 3.161V | 6.59% | Pass |
| 5VSB | 5.060V | 4.991V | 1.36% | Pass |
Advanced Transient Response at 20 Percent – 1ms
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 12.088V | 11.885V | 1.68% | Pass |
| 5V | 5.032V | 4.808V | 4.45% | Pass |
| 3.3V | 3.383V | 3.164V | 6.47% | Pass |
| 5VSB | 5.060V | 5.008V | 1.03% | Pass |
Advanced Transient Response at 50 Percent – 200ms
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 12.053V | 11.880V | 1.44% | Pass |
| 5V | 5.014V | 4.819V | 3.89% | Pass |
| 3.3V | 3.360V | 3.144V | 6.43% | Pass |
| 5VSB | 5.021V | 4.952V | 1.37% | Pass |
Advanced Transient Response at 50 Percent – 20ms
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 12.053V | 11.814V | 1.98% | Pass |
| 5V | 5.009V | 4.791V | 4.35% | Pass |
| 3.3V | 3.357V | 3.106V | 7.48% | Fail |
| 5VSB | 5.022V | 4.943V | 1.57% | Pass |
Advanced Transient Response at 50 Percent – 1ms
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 12.053V | 11.894V | 1.32% | Pass |
| 5V | 5.008V | 4.801V | 4.13% | Pass |
| 3.3V | 3.356V | 3.111V | 7.30% | Fail |
| 5VSB | 5.022V | 4.960V | 1.23% | Pass |
The transient response of the +12V rail is decent, while at 5V we would like to see a within 3% deviations. On the 3.3V rail the performance is mediocre, to say the least, since we measure over 7% deviations in two tests. Finally, the 5VSB rail performs good enough.
We didn't expect to get top results here, because of the ACRF topology.
Here are the oscilloscope screenshots we took during Advanced Transient Response Testing:
Transient Response At 20 Percent Load – 200ms
Transient Response At 20 Percent Load – 20ms
Transient Response At 20 Percent Load – 1ms
Transient Response At 50 Percent Load – 200ms
Transient Response At 50 Percent Load – 20ms
Transient Response At 50 Percent Load – 1ms
Turn-On Transient Tests
In the next set of tests, we measure the L11-CM-700’s response in simpler transient load scenarios—during its power-on phase.
For our first measurement, we turn the L11-CM-700 off, dial in the maximum current the 5VSB rail can handle, and switch the PSU back on.
In the second test, we dial the maximum load the +12V rail can handle and start the PSU while it is in standby mode. In the last test, while the PSU is completely switched off (we cut off the power or switch the PSU off through its power switch), we dial the maximum load the +12V rail can handle before 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).
We notice a voltage overshoot at 5VSB which is around 5.2V so it is within the limits. The slopes in the rest two tests are quote smooth.
