Ripple Measurements
In the following table, you will see the ripple levels that we measured on the main rails of the PT-650M. According to the ATX specification, the limits are 120 mV (+12V) and 50 mV (5V, 3.3V, and 5VSB).
Ripple Measurements FSP PT-650M |
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Test | 12 V | 5 V | 3.3 V | 5VSB | Pass/Fail |
20% Load | 29.9 mV | 22.4 mV | 22.0 mV | 12.5 mV | Pass |
40% Load | 30.8 mV | 24.0 mV | 22.5 mV | 16.5 mV | Pass |
50% Load | 31.7 mV | 24.2 mV | 22.6 mV | 16.7 mV | Pass |
60% Load | 34.2 mV | 25.1 mV | 23.3 mV | 18.5 mV | Pass |
80% Load | 39.6 mV | 26.1 mV | 30.5 mV | 20.8 mV | Pass |
100% Load | 45.5 mV | 29.7 mV | 32.2 mV | 21.2 mV | Pass |
Crossload 1 | 41.2 mV | 51.3 mV | 27.0 mV | 22.6 mV | Fail |
Crossload 2 | 36.2 mV | 28.7 mV | 27.0 mV | 19.4 mV | Pass |
Ripple suppression at normal loads is good enough. We would like to see a reading closer or even below 40 mV at +12V since this is a high-end PSU, according to FSP. During the CL1 test, the 5V rail was apparently highly stressed, leading to a ripple level that exceeded the corresponding limit. Thankfully, this test is highly unrealistic. You won't meet a similar problem in a real life scenario since the +12V rail is used almost exclusively in a contemporary PSU. All rails showed fairly good ripple suppression during the CL2 test, which is much more realistic.
Ripple at Full Load
In the following oscilloscope screenshots, you can see the AC ripple and noise that the main rails registered (+12V, 5V, 3.3V, and 5VSB). The bigger the fluctuations on the oscilloscope's screen, the bigger the ripple/noise. For all measurements, we set 0.01 V/Div (each vertical division/box equals to 0.01 V) as standard.
Ripple at Crossload 1
Ripple at Crossload 2