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Stable Voltage = Stable Operation

Getting the Right Power: 15 PC Power Supply Units
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For steady, error-free operation of the PC it is important that the voltages of the power supply unit are as stable as possible regardless of load, i.e. within the specified minimum or maximum range. Because over- or under-voltage can lead to unstable operation or even damage to the components. Processors in particular react quite sensitively to instabilities in voltage.

Therefore, for the voltage variation range, narrow limits of +/-5% of the nominal values (3.3 V, 5 V, 12 V) were set in the ATX Standard.

voltage allowed variation minimum voltage maximum voltage
+12 VDC +/- 5% +11.40 V +12.60 V
+3.3 VDC +/- 5% + 3.14 V +3.47 V
+5 VDC +/- 5% +4.75 V +5.25 V
The limits of the three power supply unit lines

When the minimum or maximum voltages of the power supply unit were exceeded or not reached, for example because individual power buses were overloaded, the power supply unit should shut down in accordance with the ATX Standard. If it does not shut down during the test under these circumstances, it scores minus points.

High Efficiency Means Energy Savings

The efficiency is defined as the ratio of output power to input power, i.e. how much energy the power supply unit takes from the outlet to supply the PC system with the necessary power. In this test, differences of up to 11% were recorded. The Seasonic SS-300FB Active PFC offered the best efficiency factor with 76%, the FSP350-60PN from Fortron Source the poorest, with 65%. This means that 14% of energy costs can be saved by operating the Seasonic device rather than the FSP350-60PN.

Quiet Operation Thanks To Regulated Fan

The high power of the power supplies goes hand in hand with enormously high heat levels. Up to 200 watts and more must be expelled in turn as heat. To ensure adequate cooling of the components of the power supply units, they have one or two fans. Many manufacturers even integrate three fans. However, in our most recent test comparison we determined that the use of three fans does not necessarily lead to lower temperatures (up to 60°C) on the interior of the devices - more is not always better.

As with CPU coolers, the fans are an irritating source of noise that make concentrated work at the PC difficult. To avoid operating noise, all manufacturers equip their devices with automatic fan control. This automatically regulates the rpm of the fan according to the temperature in the power supply unit. When the demand on the power supply unit is low, the fan accordingly revolves more slowly and is considerably quieter.

Aurora FSP350-60PN (PF): Manual choice of fan rpm through potentiometer

Some manufacturers let the user control the rpm, and thus the volume. The Aurora FSP350-60PN (PF), for example, offers not only automatic fan control but also manual control of the rpm for the rear fan. A potentiometer on the back of the power supply unit allows the rpm to be set as the user chooses.

Global Win Top-420P4: Choice of rpm on three-way switch.

Aerocool's Aero-420P4, Global Win's Top-420P4 and Vantec's VAN-400B, on the other hand, all have three-way solutions. They allow a choice between low and high rpms and automatic fan control.

Manufacturers like FSP, Seasonic and Silverstone try to increase air flow through the power supply unit while lowering the noise level by using a 120 mm fan in combination with a honeycombed rear case panel (Seasonic).

SS-300FP: honeycombed rear panel and 120 mm fan

However, in the test, only the arrangement in the SS-300FP from Seasonic proved advantageous - and then only with minimum load on the power supply unit.

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