Testing – DC Output Voltage Load Regulation

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To simulate real world operation, each power supply was connected to the 300 watt load tester, supplied with 115 VAC, and allowed to burn-in for at least 24 hrs before voltage readings were taken.  In this test we are interested in seeing how well a PSU can maintain the various output voltages while under a moderately heavy load.  The DC output voltages were measured with a FLUKE digital multimeter at the ATX connector.  The ambient air temperature during testing    was 24ºC (75ºF) +/- 1ºC.

The ATX tolerance for voltages states how much each output (rail) is allowed to fluctuate.  Most power supply manufactures try to hold tolerances tighter than this minimum specification, typically 5% instead of 10% and 1~3% instead of 5%.

Ten ATX Power Supplies Compared - Cases and Cooling 107

The following table lists the DC voltage regulation results for our 300 watt load tests.  Values in red are out of tolerance.

Ten ATX Power Supplies Compared - Cases and Cooling 108

As you can see, nearly all of the DC outputs were held within the ATX specification while operating under a 300 watt combined load.  The only two exceptions were the Enermax and Raidmax units.  Even these were on the less critical -5V and -12V outputs and were only off by 0.05V.  All of the other power supplies exhibited excellent output regulation. 

Of particular interest are the three main power rails (+3.3V, +5V and +12V) and the 5VSB line.  Maintaining these outputs at optimum levels is important to the reliable operation of any PC.  If you push components (overclock/over-volt) then they become even more critical.

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