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Transient Response Tests
Advanced Transient Response Tests
For details on our transient response testing, please click here.
Ιn these tests, we monitored the CX750M's response in two different scenarios. First, a transient load (10A at +12V, 5A at 5V, 5A at 3.3V, and 0.5A at 5VSB) was applied for 200ms while the PSU worked at 20 percent load. In the second scenario, Corsair's contender was hit by the same transient load while operating at 50 percent load. In both tests, we used 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 | 12.042V | 11.883V | 1.32% | Pass |
| 5V | 5.024V | 4.905V | 2.37% | Pass |
| 3.3V | 3.295V | 3.146V | 4.52% | Pass |
| 5VSB | 5.012V | 4.896V | 2.31% | Pass |
Advanced Transient Response at 50 Percent
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 11.977V | 11.822V | 1.29% | Pass |
| 5V | 4.992V | 4.868V | 2.48% | Pass |
| 3.3V | 3.273V | 3.116V | 4.80% | Fail |
| 5VSB | 4.957V | 4.815V | 2.86% | Pass |
The +12V rail's transient response isn't so good. We also notice large deviations on the 5VSB rail. The 5V rail performs well, but this isn't the case for the 3.3V rail, which fails to keep its load regulation within spec during the second test.
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 measured the response of the PSU in simpler transient load scenarios—during its power-on phase.
For the first measurement, we turned off the CX750M, dialed in the maximum current its 5VSB rail could output, and switched the PSU back on. In the second test, we dialed the maximum load the +12V rail could handle and started the 750W supply while it was in standby mode. In the last test, while the PSU was completely switched off, we dialed the maximum load the +12V rail could handle before switching it back 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).
There is a tiny spike at 5VSB, while the slope in the second test is very smooth. Things aren't as great in the third test, but we've seen pricier PSUs fare worse in this test, too.
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