DC Load Regulation and AC Ripple
Testing Methodology
Establishing an accurate load is critical to testing and evaluating a PC power supply. PCPerspective’s power supply test bench can place a precise DC load on the PSU under test. Each power supply is tested under controlled, demanding conditions up to its maximum rated load (at 40ºC). Our current suite of tests includes:
• DC Load Regulation
• AC Ripple and Noise
• Efficiency
• Differential Temperature
• Noise
The SilverStone Platinum ST85F-PT power supply was evaluated on both features and performance. A full range of equipment was used to test the power supply under controlled load conditions.
• (2) CSI3710A Programmable DC load (+3.3V and +5V outputs)
• (4) CSI3711A Programmable DC load (+12V1, +12V2, +12V3, and +12V4)
• (2) 200W Precision resistor load bank (+12V5 and +12V6)
• Switchable precision resistor load bank (-12V and +5VSB)
• Agilent 34401A digital multimeter (Accuracy ±0.0035% vDC)
• Extech 380803 Power Analyzer (Accuracy ±0.5% of full scale)
• DS1M12 "StingRay" digital oscilloscope (20M S/s with 12 Bit ADC)
• Powerstat Variable Autotransformer, 1.4 KVA, 0-140 VAC
• Extech Model 407738 digital sound level meter (Accuracy ±1.5 dB)
The following cables/connectors were used to connect the power supply to the PCPerspective power supply test equipment.
• (1) 20+4 pin ATX
• (2) 8-pin EPS/ATX12V
• (4) 6-pin PCI-E
• (2) SATA
• (2) Molex
DC Output Load Regulation
To simulate demanding and maximum loading conditions, the ST85F-PT power supply was connected to the load testers and supplied with a constant 120 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. We have included a second table of expanded tolerances (±1% to ±6%) for reference.
The following tables list the DC voltage results for the SilverStone Platinum Series 850W PSU while operating on 120 VAC, 60 Hz.
The power supply produced very good voltage regulation on all of the DC outputs with the three main rails staying easily within ±2% of the recommended ATX guidelines; well within SilverStone’s claimed ±3%. Well done.
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 ST85F-PT power supply also exhibited very good AC ripple and noise suppression with the results staying far below the ATX recommended guidelines, even at full load.
Did SilverStone send you the
Did SilverStone send you the PSU for review, or did you request it? If the latter, I’d say you missed an opportunity by going for the highest capacity one of the lineup. The 550W is far more interesting, as it’s one of the lowest capacity Platinum units out there, and a perfect fit for today’s high end GPUs.
The 850W model was sent to us
The 850W model was sent to us for review as SilverStone wanted to showcase the highest power in the smallest package. However, we may follow up with a review of the 550W unit. Its always nice to have the opportunity to check out more than one unit in a new series.
That would be great, hope you
That would be great, hope you are able to get one in for review.
Of course I see SilverStone’s point (850W Platinum in a smaller package than most 5-600W units is not bad at all), but high powered PSUs are less and less relevant in today’s PC builds. 3,5″ HDDs are slowly dying, multi-GPU was never really a big thing, and is quickly falling to the wayside, and >95W CPUs with actual performance to match are reserved for those with too much money to spend (although Zen might change that).
SilverStone should be lauded as one of the first PSU makers to make <700W Platinum units, but we still had a long way to go. I'm still waiting for something compact, modular and high efficiency in the 3-400W range. You can barely get 80+ Gold below 500W today.
It’s *possible* DX12 may
It’s *possible* DX12 may cause a resurgence in multi-GPU setups.. But agreed we need more gold/platinum small units.
My home (VM) server is running well with a Seasonic 360W 80plus Gold..
Sure, it’s possible, but
Sure, it’s possible, but still highly unlikely. After all, DX12 multi-GPU support is as reliant on developer support as DX11 ever was, just easier to implement (just not as reliant on driver profiles). And as always, it works on a game-to-game basis, with many lacking support. Not to mention that most PC gamers buy a single ~$200 GPU, and can’t afford multiple. Sure, the potential for improved scaling and efficiency is definitely there. I just don’t see multi-GPU having a significant resurgence.
Plus, you can easily run two GTX 1070s or RX 480s off a 600W PSU. Probably even less.
Also, there is no lack of 800W+ (heck, even 1200W+) PSUs with good efficiency today. That market is well provided for already. It’s time to provide better efficiency to the mass market.