DC Load Regulation

DC Output Load Regulation


Of course one of the first things we want to see is how well this PSU can regulate the DC outputs and maintain rock-solid voltages.  To simulate real world and maximum loading conditions, the Turbo-Cool 1200W PSU was connected to the load testers and supplied with a constant 115 VAC.  In this test we are interested in seeing how well a PSU can maintain the various output voltages while operating under different loads; all the way up to maximum rated load of 1,200W! 


The new ATX12V V2.2 tolerance for voltages states how much each output (rail) is allowed to fluctuate and has tighter tolerances now for the +12V outputs.  I have also included a second table of expanded tolerances (±1% to ±6%) for reference. 


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The following table lists the DC voltage results at seven different loads for the PC Power & Cooling Turbo-Cool 1200W PSU while operating on 115 VAC, 60 Hz.  To help minimize the voltage drop induced by the distribution wires and connectors, I used as many cables/connectors as my test setup would allow (one 24-pin ATX, two 8-pin CPU, four 6-pin PCI-E, two 4-pin Molex, and two 15-pin SATA).


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Important Note: It’s normal for the DC output voltages to decrease slightly as the load goes up.  However, the actual location for measuring voltages can have a significant impact on the voltage readings.  There are two factors, which work together to produce the resultant DC Load Regulation Voltages.  First there is the power supply’s internal ability to regulate the DC outputs as the loads change. This is what most people think of when load regulation is discussed.  Another big factor, which is frequently overlooked, is the normal voltage drop created by the distribution cables and connectors.  As the load (Amps) increases over the various cables and connectors, the greater the voltage drop created by the inherent resistance of the wires and connectors.  The resistance has a proportionately greater affect on the two low voltage rails (+3.3V and +5V) than it does on the +12V outputs.  To help compensate, the ATX12V Power Supply Design Guide requires a remote sense wire be added to 3.3V line in the ATX connector wiring harness.  PC Power & Cooling goes an extra step and adds a remote sense wire to the +5V output as well.


To help illustrate this point, I measured the DC output voltages at the component side of the 24-pin ATX connecter (my standard test point) and also back at the power supply’s PCB.  The DC output voltages measured at the ATX connector include both the PSU’s internal regulation and voltage drops caused by the wire and connector resistance. 


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As you can see, the Turbo-Cool 1200W PSU produced very good load regulation on all of the outputs across a broad range of loads; all the way up to 1,200 watts.  As expected, while delivering almost 17A the +3.3V rail showed the largest change but easily stayed within spec.  The three primary voltages (+12V, +5V and +3.3V) were rock-solid, exhibiting excellent load regulation.  Even when measured at the 24-pin ATX connector, these voltages were within ±3% and when the wire and connector losses were excluded, the +12V rail was closer to -1%; very good!

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