DC Load Regulation and AC Ripple

DC Output Load Regulation

To simulate real-world  and max loading conditions, the Corsair CS850M 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. 

The 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.

The following tables list the DC voltage results for the PSU while operating on 115 VAC, 60 Hz.

The CS Series Modular 850W PSU produced very good load regulation on all three of the main outputs (+3.3V, +5V and +12V) across a broad range of loads; staying within ±2%.   

AC Ripple and Noise on the DC Outputs

The amount of AC ripple and noise present on the DC outputs was checked using a digital oscilloscope.  This AC component may be present in the KHz range where most switching power supplies operate or it may be more prevalent at the 60 Hz line frequency.  We adjust the O-scope time base to look for AC ripple at both low and high frequencies.  The ATX12V V2.2 specification for DC output noise/ripple is defined in the ATX12V Power Supply Design Guide.

Ideally we would like to see no AC ripple (repetitive) or noise (random) on the DC outputs – the cleaner the better!  But in reality there will always be some present.  I measured the amplitude of the AC signal (in millivolts, peak-to-peak) to see how well the power supply complied with the ATX standard.  The following table lists the ripple/noise results during all of the load tests for the main output voltages of interest.

The AC ripple and noise suppression results for the Corsair CS850M PSU were also very good with all of the rails staying well below 50% of the max recommended guidelines. The AC ripple on the +12V output almost doubled going from test #4 to test #5, indicating the CS850M is nearing the high end of its design range.

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