DC Load Regulation and AC Ripple

DC Output Load Regulation

To simulate demanding and maximum loading conditions, the EVGA SuperNOVA 550 GS and 650 GS power supplies were 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.

SuperNOVA 550 GS:

SuperNOVA 550 GS: The following tables list the DC voltage results for the 550 GS PSU while operating on 115 VAC, 60 Hz.

The 550 GS produced very good voltage regulation on the three primary DC outputs with the measured values falling within the ±2% tight voltage regulation range that EVGA claims for their new GS units.

SuperNOVA 650 GS:

SuperNOVA 650 GS: The following tables list the DC voltage results for the 650 GS PSU while operating on 115 VAC, 60 Hz.

The 650 GS also produced very good voltage regulation on the three primary rails, again staying easily within the claimed tight voltage regulation parameters of ±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.

SuperNOVA 550 GS:

The 550 GS power supply exhibited very good AC ripple suppression on all of the primary outputs, all the way up to full load. The +3.3V and +5V rails were extremely well behaved while the +12V output started to exhibit a little more ripple and noise than we have seen on some other high-end EVGA PSUs, but still stayed well below 50% of the recommended guidelines.

SuperNOVA 650 GS:

The results for the 650 GS power supply were nearly identical to the 550 GS.

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