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smartphones, tablets, printers, Internet
hubs, routers, and IoT gateways. Given
the expectation for explosive growth in
IoT applications, the Level VI specification
for external power supplies could be seen
as providing valuable protection for the
environment against the effects of the
large numbers of IoT gateways soon to
be connected to the power grid.
CUI began introducing Level VI products
to its EPS range in late 2014, to address
the new regulation. EPS manufacturers
typically adjust their product portfolios
to meet the highest mandatory standard,
which enables OEM customers to maximize
operational efficiency and eliminate
supply-chain errors by shipping a common
power supply type with products destined
for multiple export markets.
The Level VI protocol is significantly
more complex than its predecessors,
and defines five categories of adapters
including, for the first time, units rated
over 250 W. Table 1 lists the specified no-
load power and average efficiency for all
categories covered.
Typical IoT gateways are unlikely to
require a 250 W or multi-output adapter,
but could be designed for use with a
single-voltage AC/DC supply of above
6V or a sub-6V low-voltage supply in the
under-1W or 1W-49W category. Figure 1
compares the minimum average efficiency
specifications for Level VI single-voltage
(output > 6V) power adapters against
the Level III, Level IV and Level V
specifications. The limit is significantly
higher for units in the 0.5W-5W range
that will likely power a large proportion of
diode rectification. Other component
changes include re-optimized resistance
values, and the use of increased wire
gauges to reduce internal power
dissipation. Moreover, newer MOSFETs
with lower on-state resistance help to
raise efficiency at heavier loads.
On the other hand, the main power
circuitry is arranged in much the same
way as the previous Level V units. Units
rated below 120 W use CUI’s established
flyback design, while adapters over
120 W use LLC resonant topology. It is
worth noting that the increased average
efficiency of the Level VI power supplies
also helps to reduce the typical working
temperature thereby boosting reliability.
This can be a particularly important
advantage in IoT applications, where
equipment often is required to operate
for long periods in the field with little or
no maintenance.
Improvements for IoT and
Environment
The US Environmental Protection
Agency (EPA) has said the regulations
imposed on external power supplies
over the last decade have already cut
CO2 emissions by more than 24 million
tons per year and saved households $2.5
billion annually. The US Department of
Energy now believes enforcing Level VI
will save around 47 million tons of CO2.
Manufacturers of equipment such as
IoT gateways need to keep abreast of
the latest standards applicable to power
supplies and energy.
Figure 1. The Level VI minimum average
efficiency requirement is significantly higher
than in previous specifications
IoT gateway devices. Depending on the
application the gateway may be designed
to make use of sleep modes, taking
advantage of the lower no-load power
consumption of the Level VI specification.
Other applications may
require the gateway to be active more or
less continuously.
Meeting Level VI by Design
The new Level VI specifications present
tough challenges to power supply
designers. Compared with CUI’s Level
V power supplies, the Level VI units
incorporate changes to almost every
aspect of the primary and secondary-
side circuitry. These have included
designing-in the latest control ICs that
support enhanced light-load operating
modes: in normal operation the new
controllers operate at the same 65 kHz
switching frequency used in the Level V
products, but change to 22 kHz at light-
load and no-load to reduce power loss
and improve efficiency. The capacitor and
resistor values in the secondary feedback
circuit have also been re-optimized to
mitigate the effects of increased ripple
and noise at lower switching frequencies.
The control IC also takes advantage of
new technologies to reduce quiescent
power, which contributes further towards
meeting the tougher maximum limits on
no-load power consumption.
Changes in the secondary-side circuitry of
low-voltage/high-current Level VI power
supplies include adopting synchronous
rectification using MOSFETs and a
dedicated control IC, in place of simple
Table 1. Summary of no-load and dynamic efficiency targets
for Level VI marking protocol
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