How to Select a High Efficiency Power Supply

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Power Buyers Guides

Basic terms of how to choose the right power supply.

Efficiency is sometimes confused with effectiveness. A system that produces exactly what it is meant to and wastes most of its input power is effective, but not efficient. Electrical efficiency is the ratio of how well the power supply is able to convert the input power it receives from the wall to the output power it feeds to the devices. For example, if a device uses 360W, but the power supply pulls 450W from the wall, then the efficiency is 360W/450W, which is 80%. If a power supply has 90% efficiency with the device having the same usage of 360W, it would draw 400W.

Why is efficiency important? One of the most important benefits for more efficient power supplies is to consume less power. This reduces the demand for energy from polluting sources, saving resources and money. In the example mentioned earlier, if the power supply was only 60% efficient, it would draw about 600W compared to the 400W at 90% efficiency. Saving 200W leads to much smaller usage of power and a lower utility bill.

Another important reason for efficiency in power supplies is to lower heat loss with each use. Heat is the number one enemy to a power supply containing sensitive capacitors, transistors and other elements. Heat changes the lifetime and reliability of the power supply by decreasing the duration of those components by as much as 50% for every 10°C increase in temperature. An excessive temperature rise in any of these elements can result in premature failure of the power supply.

Mean Well HLG-120-12A Power Supply
Mean Well HLG-120-12A Power Supply

Mean Well HLG-80H-15B Power Supply
Mean Well HLG-80H-15B Power Supply

High efficiency power supplies are at least 75% efficient but can reach as high as 93%. Power supplies are never 100% efficient since there is always heat loss requiring cooling methods. Higher efficiencies are achieved by the way the power supply is cooled and with power factor correction (PFC). Some power supplies are cooled by a built-in fan (Mean Well's LRS series) while others are fanless (Mean Well's RS series) and are instead cooled by free air convection. The LRS series has an efficiency range of 79% to 90%, while the RS series is rated at 74% to 87%.

The power factor is the ratio of the actual power flowing to the load to the apparent power, which is the product of the current and voltage of the circuit. A high power factor is desirable to help reduce transmission losses and improve voltage regulation at the load, which is efficiency. The PFC will help increase the power factor of the supply. Mean Well's HSP series has a built in PFC function with efficiency ranges of 86% to 90% while the HRP series has both a built-in fan and PFC function and ranges of 80% to 89% efficiency.

These are some of the things to consider in terms of efficiency when selecting a power supply. For more information head to the Jameco Power Resource Center.