Transient Response Tests
Advanced Transient Response Tests
For details on our transient response testing, please click here.
Ιn these tests, we monitor the TPG-0850D-R'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) is applied for 200ms while the PSU works at 20 percent load. In the second scenario, Thermaltake's contender 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 | 12.089V | 11.968V | 1.00% | Pass |
| 5V | 5.021V | 4.931V | 1.79% | Pass |
| 3.3V | 3.318V | 3.206V | 3.38% | Pass |
| 5VSB | 4.997V | 4.861V | 2.72% | Pass |
Advanced Transient Response at 50 Percent
| Voltage | Before | After | Change | Pass/Fail |
|---|---|---|---|---|
| 12V | 12.049V | 11.916V | 1.10% | Pass |
| 5V | 4.972V | 4.883V | 1.79% | Pass |
| 3.3V | 3.280V | 3.180V | 3.05% | Pass |
| 5VSB | 4.939V | 4.797V | 2.88% | Pass |
The +12V rail approaches 1%. This is an acceptable deviation, though in this category we'd like to see close to 0.5% readings on this rail. The 5V and 3.3V rails encounter controlled voltage drops, however the latter rail drops below 3.2V during the second test because of its low initial voltage. Finally, the 5VSB rail performs poorly in these tests.
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 TPG-0850D-R, 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 850W 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).
The 5VSB rail behaves well. During the second test, the +12V rail's slope does a small wave that we aren't worried about. The last test is really bad though, with the +12V rail dropping its output close to zero for for several milliseconds. This is something that we didn't expect to see from a PSU that costs $180 (at the time of the review). Needless to say, such a bad result will cost the PSU several performance points. Thankfully, going from off to full load is almost impossible to reproduce under real-world conditions. But the TPG-0850D-R should still be able to handle this scenario without a problem.