Noise and Ripple can easily be measured by an oscilloscope. These show how much voltage fluctuation there is on a particular rail. We tested the rail stability of the 3.3 volt, 5 volt and 12 volt rails using an identical time and millivolt scale for all graphs. millivolt ripple is measured by the peak to peak size of the voltage curve.
Sample Ripple Graph
The latest ATX 12 volt version 2.3 specifications state that ripple from peak to peak must be no higher than 50 millivolts for the 3.3 volt and 5 volt rails, while the 12 volt rail is allowed up to 120 millivolts peak to peak to stay within specifications. Millivolt figures are stated to the closest increment of 5 given their variability.
| Load (%) | 3.3V Ripple | 5V Ripple | 12V Ripple |
| 20 | 7mV | 5.2mV | 14.6mV |
| 40 | 8.6mV | 6.6mV | 18.4mV |
| 60 | 11mV | 8.8mV | 23.2mV |
| 80 | 13.8mV | 12.2mV | 31.2mV |
| 100 | 16.6mV | 12.8mV | 35.8mV |
Ripple suppression was excellent for such a compact unit; less than 40 mV on the 12 volt and around 15mV on the other main rails is an excellent result. We see results similar to this on higher end ATX units.
3.3 volt @ 100%
5 volt @ 100%
12 volt @ 100%
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