IEEE Power Electronics Magazine - March 2017 - 20

It was not uncommon for these adapters to waste nearly 1
consumption based, calculating a product's allowable
W or more while in no-load mode.
annual total energy consumption (TEC), in kilowatt
The first major EPS efficiency specification to emerge
hours per year, based on a product's typical daily usage.
was the EC's CoC [2], minimizing no-load power losses
Early regulations simply focused on modal power conin EPSs rated at 75 W and below output. The CoC's initial
sumption limits, but newer TEC regulations are more
no-load limit (effective January 2001) was 1 W, dropping
complex, placing more importance on the design of the
down to 0.75 W in 2003. These limits caused some power
power supply to be efficient during a wide range of opersupply design change, but linear transformer designs
ating load points. Some regulations use a combination of
could still be modified to meet those
both modal and TEC limits.
no-load requirements.
It is valuable to understand that
In January 2005, a more comprethe overall efficiency of a mainsWithout these regulahensive ENERGY STAR EPS efficiency
powered product is determined by
program specification became effecthree equally important parts: 1) the
tions demanding higher
tive, adding a minimum average activeac-dc power conversion stage, 2) the
efficiency, we might
mode efficiency requirement (based
efficiency of the rest of the electronic
on the measured average efficiency
circuitry during the product's main
still be using large,
at 25, 50, 75, and 100% load points) [3].
function operation, and 3) power manbulky adapters.
Desiring harmonization, the CoC veragement controls, allowing a product
sion 2 adopted the ENERGY STAR
to automatically go into lower-power
approach and test method. Although
operating modes (i.e., idle, sleep, or
the CoC and Energy Star were voluntary programs, the test
off) when not in use. In some cases, when automatic power
method and metrics were adopted for mandatory standards
down can move a product into such a low-power mode, the
by the CEC, U.S. DOE, and EC Ecodesign Directive. (The
reduced efficiency of the power supply at that low level can
ENERGY STAR EPS efficiency program was suspended in
cause unintended overtemperature and/or noise problems.
December of 2010.) These tighter, mandatory requirements
Regulations targeting item 1) directly impact power supply
provided the catalyst for power supply design change, espeefficiency, whereas those targeting items 2) and 3) indicially in the 2-12 W area for personal electronic adapters,
rectly affect power supply efficiency.
and transformed the market away from linear designs to
switch-mode designs. In addition to efficiency gains, the
Regulations Directly Impacting
new designs delivered lighter and smaller external power
Power Supply Efficiency
supplies and adapters, as shown in Figure 1. The large
Direct impact regulations specifically target external power
1990s preregulation mobile phone adapter [Figure 1(a)] has
supply (EPS) and internal power supply (IPS) conversion
a no-load power consumption of almost 1 W compared to
efficiency. As a result of the rise of personal mobile electhe 2016 smartphone adapter [Figure 1(c)], with a no-load
tronics (cell phones, MP3 players, laptops) in the 1990s,
consumption of less than 0.03 W. Without these regulations
power adapters started invading our homes and offices in
demanding higher efficiency, we might still be using large,
large numbers. Most were based on decades-old bulky linbulky adapters.
ear transformer technology design, barely squeaking by
In the beginning, changing from a linear-based power
with 50% conversion efficiency at full load and consuming
supply design to a switching power supply design was a
measurable power when the adapter was plugged into the
quick way to become compliant. But in 2016, the U.S DOE
wall but not attached to its end application (no-load mode).
EPS Level VI EISA standard and EC CoC version 5 program
brought tighter no-load power consumption and higher
Before EPS
active-mode efficiency requirements. The new regulations
Efficiency Programs
EPS
Efficiency
required power supply designers to consider additional
Pout = 2.26 W
EPS Efficiency
Level VI
circuit changes. Examples include the following:
Level V
Pout = 18.0 W
■■Modified switching algorithms. As agencies became
Pout = 5.0 W
aware that some applications (computers) spend a major
part of the day in nonactive modes (i.e., idle or standby
modes), they realized that power supplies also needed to
be highly efficient at those low-load levels. Results from
(a)
(b)
(c)
a study conducted by the International Telecommunication Union [4] that were presented at a 2012 CoC EPS
meeting revealed a noticeable efficiency drop at load levels that were 10% and below in power supplies that otherwise exhibited high efficiency at higher loads. This
FIG 1 (a)-(c) The EPS efficiency program affect on personal
resulted in the addition of a separate minimum
electronic adapters.

IEEE PowEr ElEctronIcs MagazInE

z March 2017

Table of Contents for the Digital Edition of IEEE Power Electronics Magazine - March 2017