POWER


Table 1: 80 Plus Effi ciency Levels for internal ac/dc power supplies


has a maximum value of one. Real power, measured in watts, refers to the power that does work and is consumed by the power supply and load. 90 degrees out of phase with the real power is reactive power, measured in volt-amps reactive (VAR). Reactive current simply circulates in the system doing no work. Apparent power is the magnitude of the vector sum of the real and apparent power, which is also equal to the product of rms voltage and current. In a purely resistive circuit, the power factor is 1 and all of the apparent power produces work. However, when reactive components, such as inductors and capacitors, are introduced into circuits and loads, the current waveform will shift with respect to the voltage and the power factor will drop due to the addition of reactive power. In non-linear circuits, such as switching power supplies, there are also harmonics to worry about. Harmonic current is reactive and therefore also lowers power factor. The impact of low power factor is increased input current; this leads to: • • • •


Larger and more expensive cabling Distribution networks


Reduced capacity on branch circuits Increased cost


There are many reasons a designer would choose an 80 Plus certifi ed power supply over others that are not certifi ed. A large reason is cost. Higher effi ciency supplies translate into less wasted power. This means


more effi cient power supplies can help reduce the cost of running larger facilities. Wasted power is generally dissipated in the form of heat, often necessitating cooling systems that not only add cost, but can take up precious space and create unnecessary noise. Less heat and fewer, or no, running fans also help extend a product’s life and the overall reliability of a system.


History of the Levels of the Program As the name implies, when the 80 Plus certifi cation was fi rst introduced, it only required that power supplies be at least 80% effi cient at 20% load, 50% load, and 100% load. This level of effi ciency is now known as 80 Plus Basic. Since the program’s introduction fi ve additional levels of certifi cation have been added. The 80 Plus program now consists of the following levels of certifi cation:


Each of these certifi cations is further divided up into sub-categories based on AC input voltage. This helps manufacturers target different regions of the world. These subcategories include: • • • • •


115V internal non-redundant 230V internal redundant 115V industrial


230V EU internal non-redundant 380V DC


The different levels of certifi cation, along with 3 of the different sub-categories, are outlined in the table below. It is also


worth pointing out that the highest level of certifi cation, 80 Plus Titanium, introduced an additional rated load of 10%.


Power supplies are generally the most


effi cient between 50% and 75% of their rated loads. However, at lighter loads, power supply effi ciency can drop signifi cantly. Indeed, with the exception of Titanium rated supplies, any 80 Plus certifi ed supply can drop below 80% effi ciency at loads below 20%. With that said, the Titanium level of certifi cation requires that all supplies be at minimum 90% effi cient at 10% of their rated load.


Importance of High Effi ciency Reducing power consumption, being green or environmentally friendly, is a benefi t in itself, but improving the effi ciency of power supplies is also important for cost. Server farms and data centers can save a substantial amount of money by integrating more effi cient power supplies into their systems.


Wasted power is calculated with the following equation: P_waste = (P_out/effi ciency) – P_out = Pin - Pout


So, for example, a 375W supply - Platinum certifi ed supply would waste 41.67W of power at full load. This assumes a 230V non-redundant supply with 90% effi ciency. On the other hand, an equivalent 375W supply that is Titanium rated (94% effi ciency)


MARCH 2024 | ELECTRONICS FOR ENGINEERS 27


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