DC Load Regulation and AC Ripple

DC Output Load Regulation

To simulate real world and maximum loading conditions, the Corsair AX1500i 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.

As you can see, the AX1500i produced outstanding load regulation on all of the outputs across a broad range of loads. Corsair isn’t kidding when they claim ±1.0% regulation on the +12V rail. Even when delivering over 100 amps, the +12V rail stayed well within ±1.0%. These are the best voltage regulation numbers we have seen from any power supply tested to date!

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 AX1500i PSU were also outstanding with all of the rails staying way below the max recommended ATX guidelines and well within Corsair’s claimed less than 30mVpk-pk for the +3.3V and +5V rails and less than 40mVpk-pk for the others. Again, these are outstanding numbers and among the best we have seen to date, especially for these power levels.

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