Line Regulation and Cross-LoadingDC Output Line Regulation
In this test we are interested in seeing how well a PSU can maintain the various output voltages while the AC input line voltage changes. In the previous Load Regulation test, the AC line voltage was held constant at 115 VAC. Now we will look at how much the DC outputs change as the load is held constant and the AC line voltage is changed from 120 VAC down to 90 VAC.
The SS-400H1U and SS-460H2U Line Regulation tests were performed with the combined DC loads set to 300W and 340W respectively. The AC input voltage to the power supply (via the Extech power analyzer) was adjusted using a Powerstat variable autotransformer. We observed virtually no measurable change in either of the two PSU’s DC outputs.
PC switching mode power supplies provide multiple DC output voltages. Ideally, the total load should be distributed across all the main outputs (+3.3V, +5V, +12V). This means that the combined +3.3V and +5V load should be proportional to the combined +12V load – as one increases, so should the other. Unfortunately, this is not always the case, especially in newer PCs that predominately use +12V and may put only minimal loads on the +3.3V and/or +5V rails.
Cross-loading refers to imbalanced loads. If a PC pulls 400W on the +12V outputs and only 40W (or less) on the combined 3.3V and +5V outputs, the resulting voltage regulation may suffer.
Neither of the two Seasonic PSUs had any problems handling our cross-loading tests. In the first test we put a heavy load on the +12V outputs and a light load on the remaining outputs. Even with this large imbalance, the voltages all stayed well within spec.
In the second test we reversed the cross-load and placed a heavy load on the +3.3V and +5V outputs with a light load on the +12V rail. Once again, the PSUs passed these tests without problems with all the voltages looking very good.