Advanced Transient Response Tests
In these tests, we monitor the response of the PSU 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 to the PSU for 200 ms while the latter is working at 20% load. In the second scenario, the PSU, while working at 50% load, is hit by the same transient load. We measure the voltage drops the transient load causes with our oscilloscope in both tests. Voltages should remain within the regulation limits defined by the ATX specification.
Real-world usage always has a PSU work with loads that change depending on whether the CPU or graphics cards are busy, which makes whether the PSU can keep its rails within the ranges defined by the ATX specification important. The smaller the deviations, the steadier the system will be, which results in less stress being applied to its components.
We should note that the ATX specification requires for capacitive loading during the transient tests, but in our methodology, we chose to apply the worst-case scenario with no extra capacitance on the rails. Although the ATX specifications asks for this capacitance, your system—the mainboard and its other parts—may not provide it, which we have to keep in mind as well.
Advanced Transient Response 20% - 5 Hz |
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Voltage | Before | After | Change | Pass/Fail |
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12 V | 12.050V | 11.945V | 0.87% | Pass |
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5 V | 5.039V | 4.960V | 1.57% | Pass |
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3.3 V | 3.292V | 3.172V | 3.65% | Pass |
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5VSB | 5.034V | 4.982V | 1.03% | Pass |
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Advanced Transient Response 50% - 5 Hz |
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Voltage | Before | After | Change | Pass/Fail |
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12 V | 12.025V | 11.938V | 0.72% | Pass |
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5 V | 5.027V | 4.943V | 1.67% | Pass |
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3.3 V | 3.281V | 3.154V | 3.87% | Pass |
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5VSB | 5.008V | 4.957V | 1.02% | Pass |
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The transient response at +12V is satisfactory, but I would like to see lower voltage drops on the 3.3V rail.
Below are the oscilloscope screenshots we took during Advanced Transient Response testing.
Transient Response at 20% Load
Transient Response at 50% Load
Turn-On Transient Tests
We measure the response of the PSU in more straightforward scenarios of transient load, during the power-on phase of the PSU, in the next set of tests. In the first test, we turn the PSU off, dial 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 the PSU is 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% of their nominal values (e.g., +10% for 12V is 13.2 V and 5.5 V for 5V).
Good performance here.
Ripple Measurements
Ripple represents the AC fluctuations (periodic) and noise (random) found in the DC rails of PSUs. Ripple significantly decreases the life span of capacitors because it increases their temperature; a 10 °C increase can cut into a capacitor's life span by up to 50 percent. Ripple also plays an important role in overall system stability, especially when it is overclocked. The ripple limits according to the ATX specification are 120 mV (+12V) and 50 mV (5V, 3.3V, and 5VSB).
Ripple Measurements Thermaltake TPD-0850F3FAGU-1 |
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Test | 12 V | 5 V | 3.3 V | 5VSB | Pass/Fail |
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10% Load | 7.4 mV | 11.8 mV | 9.2 mV | 13.4 mV | Pass |
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20% Load | 15.1 mV | 11.3 mV | 8.6 mV | 13.2 mV | Pass |
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30% Load | 17.3 mV | 11.7 mV | 9.1 mV | 13.8 mV | Pass |
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40% Load | 13.6 mV | 11.8 mV | 9.5 mV | 13.3 mV | Pass |
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50% Load | 12.9 mV | 13.0 mV | 10.3 mV | 14.0 mV | Pass |
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60% Load | 11.3 mV | 12.0 mV | 9.8 mV | 14.4 mV | Pass |
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70% Load | 12.0 mV | 12.4 mV | 11.1 mV | 16.4 mV | Pass |
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80% Load | 11.7 mV | 13.1 mV | 12.0 mV | 18.6 mV | Pass |
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90% Load | 11.9 mV | 12.7 mV | 12.4 mV | 19.2 mV | Pass |
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100% Load | 18.3 mV | 13.8 mV | 13.9 mV | 21.8 mV | Pass |
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110% Load | 18.4 mV | 13.3 mV | 14.2 mV | 20.6 mV | Pass |
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Crossload 1 | 9.1 mV | 12.4 mV | 11.4 mV | 15.9 mV | Pass |
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Crossload 2 | 18.0 mV | 13.0 mV | 12.0 mV | 19.0 mV | Pass |
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Low ripple on all rails.
Ripple at Full Load
Ripple at 110% Load
Ripple at Crossload 1
Ripple at Crossload 2