Line Regulation and Cross-Loading

DC 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 AC line voltage is changed from 120 VAC down to 90 VAC.


PC Power & Cooling Turbo-Cool 1200W PSU Review - Cases and Cooling 48 


The Line Regulation test was performed with the combined DC loads set to 600W.  The AC input voltage to the power supply (via the Extech power analyzer) was adjusted using a Powerstat variable autotransformer. 


No measurable change in the DC outputs; like a rock.


Note: 90VAC is actually 10VAC below the minimum AC line voltage spec for the Turbo-Cool 1200W PSU.


Cross-Loading Test


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 500W on the +12V outputs and only 50W (or less) on the combined 3.3V and +5V outputs, the resulting voltage regulation may suffer.


PC Power & Cooling Turbo-Cool 1200W PSU Review - Cases and Cooling 49 


Thanks to the unique design of the Turbo-Cool 1200W, the unit is virtually unaffected by cross-loading.  In the first test we put a heavy load (80A/960W) on the +12V output and a light load on the remaining outputs.  Even with this large imbalance, the voltages all look very good.


In the second test we reversed the cross-load and placed a heavy load (154W) on the +3.3V and +5V outputs with a light load (2A/24W) on the +12V rail.  Once again, the Turbo-Cool 1200W PSU passed this test without problems.

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