SQUEEZING EVERY DROP!
New power management architectures look set to shake-up the
world of energy harvesting, reports Mike Seren
The Internet of Things (IoT),
Industry 4.0, digital health and
greater prevalence of wearable
electronics all rely heavily on the
use of sensing devices that it simply
won’t be practical to plug into a mains
socket.
Having to regularly replace
batteries can prove impractical though,
especially if sensors are situated in
remote or dif cult to access locations.
Interest in energy harvesting
technology has been growing for many
years, with new implementations
being based on thermal gradients,
photovoltaics, vibrational forces, RF,
etc. The rate at which these are being
initiated, however, is still relatively low,
which suggests that things have not
matured as quickly as was originally
envisioned with underlying doubts
holding back widespread adoption.
How to glean enough energy
is proving dif cult, plus there are
perhaps still some lingering concerns
about the returns on investment.
At Embedded World earlier this
year, Dr Peter Spies of the Fraunhofer
IIS, talked to New Electronics about
the research his team are heavily
involved in developing next generation
microelectronic solutions for energy
harvesting purposes, with a broad
variety of industrial use cases being
covered.
According to Dr Spies, “One of the
issues with extracting energy from
the surrounding environment is, of
course, that it is not constant. In most
situations, external conditions will
keep changing over time and therefore
so will the output levels that are
available.
“This is why effective power point
tracking and impedance matching are
both so vital.
“Another issue to be aware of is
that the characteristics of deployed
energy harvesting apparatus will also
vary considerably, from one unit to
another.”
According to Dr Spies, “For all
of these reasons having access to
sophisticated power management is
of critical importance. It
will let the system adapt
so that it better addresses
the speci c energy pro le.
This will permit the largest
possible amount of
energy to be drawn by the
system and ensure that
operational ef ciency
gures are maximised.”
One of the major
challenges faced
by companies and
organisations involved in
the power management
aspect of energy
harvesting is trying to keep the
start-up voltage, needed to activate
devices, as low as possible.
The lower the threshold at which
energy can start to be extracted,
the better the chance the system is
able to survive without dependency
on current from a depleting battery
source.
Rather than trying to tackle the
problem through novel semiconductor
processes, the Fraunhofer IIS team
have concentrated their efforts
on creating innovative power
architectures.
At their heart is DC/DC converter
circuitry which is based on the
utilisation of a Meissner oscillator
connected to a JFET (or in some cases
a zero threshold MOSFET).
A key differentiator here is that the
diodes which would normally feature
in such an arrangement are replaced
by MOSFETs (since they don’t have
the same voltage drop issues). As a
result, far greater degrees of ef ciency
can be realised (reaching over 90%),
and it also enables energy extraction
to be initiated at much lower levels.
Figure 1: Example
of a Fraunhofer IIS
energy harvesting IC
In relation to thermally-oriented
energy harvesting, for example,
this has allowed the institute’s
thermoelectric generator (TEG)
implementations to produce currents
from just a few Kelvins of temperature
difference (needing only a tiny
20mV start-up voltage), and at peak
performance outputting up to 100μW
of power per Kelvin.
With additional active recti ers,
built using MOSFETs instead of
diodes, these TEGs even permit
current to be drawn from negative
thermal gradients.
Inventive topologies
e-Peas, a Belgian rm, that has gained
considerable market traction with
large scale deployments in numerous
industrial sites, as well as success
in livestock tracking applications,
has developed a topology which sees
self-oscillating loops incorporated
into each of its AEM series power
management ICs, to facilitate start-up
at the earliest feasible stage (and
eliminate the need for a gate driver
“Another issue
to be aware
of is that the
characteristics
of deployed
energy harvesting
apparatus
will also vary
considerably,
from one unit to
another.”
Dr Peter Spies
20 28 April 2020 www.newelectronics.co.uk
/www.newelectronics.co.uk