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Ripple Measurements
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The following table includes the ripple levels we measured on the ST45SF's rails. The limits, according to the ATX specification, are 120mV (+12V) and 50mV (5V, 3.3V and 5VSB).
| Test | 12V | 5V | 3.3V | 5VSB | Pass/Fail |
|---|---|---|---|---|---|
| 10% Load | 13.3mV | 10.8mV | 17.0mV | 7.7mV | Pass |
| 20% Load | 21.4mV | 13.8mV | 18.7mV | 10.0mV | Pass |
| 30% Load | 17.5mV | 16.0mV | 21.3mV | 11.5mV | Pass |
| 40% Load | 20.2mV | 17.4mV | 25.0mV | 13.4mV | Pass |
| 50% Load | 24.9mV | 19.8mV | 26.0mV | 14.2mV | Pass |
| 60% Load | 26.8mV | 21.1mV | 24.9mV | 17.3mV | Pass |
| 70% Load | 29.6mV | 23.6mV | 28.6mV | 19.7mV | Pass |
| 80% Load | 35.6mV | 25.6mV | 36.7mV | 23.9mV | Pass |
| 90% Load | 41.3mV | 28.1mV | 41.4mV | 25.1mV | Pass |
| 100% Load | 50.2mV | 32.7mV | 40.8mV | 29.7mV | Pass |
| 110% Load | 60.3mV | 32.7mV | 42.5mV | 31.1mV | Pass |
| Cross-Load 1 | 23.7mV | 33.2mV | 37.5mV | 29.3mV | Pass |
| Cross-Load 2 | 51.8mV | 18.8mV | 32.6mV | 11.9mV | Pass |
Ripple suppression is decent on every rail except 3.3V, where it exceeds 40mV under full load. To be fair, we did tax this small PSU with an almost-46°C operating temperature during the full load and overload tests.
Ripple Oscilloscope Screenshots
The following oscilloscope screenshots illustrate the AC ripple and noise registered on the main rails (+12V, 5V, 3.3V and 5VSB). The bigger the fluctuations on the screen, the bigger the ripple/noise. We set 0.01 V/Div (each vertical division/box equals 0.01V) as the standard for all measurements.
Ripple At Full Load
Ripple At 110-Percent Load
Ripple At Cross-Load 1
Ripple At Cross-Load 2
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