Transient Response Tests
Advanced Transient Response Tests
For details on our transient response testing, please click here.
Ιn these tests, we monitor the CX650M's response in two different scenarios. First, a transient load (10 A at +12V, 5 A at 5V, 5 A at 3.3V, and 0.5 A at 5VSB) is applied for 200ms while the PSU works at 20 percent load. In the second scenario, the CX650M 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 very tough to master, especially for a PSU with a capacity of less than 500W.
Advanced Transient Response at 20 Percent
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 12.094V | 11.938V | 1.29% | Pass |
| 5V | 5.021V | 4.966V | 1.10% | Pass |
| 3.3V | 3.287V | 3.185V | 3.10% | Pass |
| 5VSB | 5.066V | 5.030V | 0.71% | Pass |
Advanced Transient Response at 50 Percent
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 12.048V | 11.893V | 1.29% | Pass |
| 5V | 5.007V | 4.952V | 1.10% | Pass |
| 3.3V | 3.276V | 3.157V | 3.63% | Pass |
| 5VSB | 5.030V | 5.001V | 0.58% | Pass |
It would be nice if the +12V deviations stayed within 1%, but we can't be that picky with such an affordable PSU. The 5V and 5VSB rails have low deviations, while 3.3V registers the worst performance. In both tests the 3.3V rail drops its voltage below 3.2 V as soon as the transient load is applied.
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 measure the PSU's response in simpler transient load scenarios—during its power-on phase.
For the first measurement, we turn off the PSU, dial in the maximum current the 5VSB can output, and switch it back on. In the second test, we dial the maximum load the +12V rail can handle and start the PSU while it's in standby mode. In the last test, while the CX650M is completely switched off, 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 13.2 V, and 5.5 V for 5V).
The 5VSB slope is perfect. The +12V slopes are pretty good as well, with the last one featuring a very brief period of increased ripple. That's nothing to worry about, though.
