Efficiency, Differential Temperature and Noise


Efficiency is defined by the power output divided by the power input and is usually expressed as a percentage.  If a PSU were a 100% efficient (which none are) 500 watts of AC power going in would result in 500 watts of DC power coming out (with no waste heat to dissipate).  In the real world there are always inefficiencies and power is lost in the form of heat during the conversion process. Newer revisions to the ATX12V Power Supply Design Guide V 2.2 have continued to increase the efficiency recommendations for PC switching mode power supplies and now lists both required and recommended minimum efficiencies.

We measured the AC power input to the Nightjar NJ520 PSU with an Extech power analyzer while the total DC load was found by adding all the individual +3.3V, +5V, +12V, -12V and +5VSB loads together.  

The overall efficiency of the Nightjar NJ520 power supply is also excellent and meets the criteria for 80Plus Platinum certification, even while operating on 115 VAC and at elevated temperatures.

80 Plus Program

    Note: Tests conducted at room temperature (25°C)

Differential Temperature and Noise Levels

To measure the differential temperature of the NJ520 during testing we placed one thermocouple over the top of the power supply in a modified case with the top panel removed (T out). A second thermocouple measured the ambient air temperature at the bottom of the PC enclosure (T in). The ambient room air temperature was ~23ºC (74ºF) during testing.

T out = temperature of air exhausting from power supply
T in = temperature of air entering power supply
Delta T = T out – T in

Because the NJ520 is fanless and incorporates no moving parts the PSU is essentially silent during normal operation.

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