Vito Kortbeek and Przemysław Pawełczak
As energy harvesting has become more
prevalent for low-voltage IoT and smart devices,
chip makers have integrated the discrete
components required to efficiently harvest
the most energy possible onto a single chip to
optimize size and performance. Now, anyone
can buy chips and breakout boards from Digi-
Key, SparkFun, and Adafruit that can harvest
solar, piezoelectric, thermal, and even radio
wave energy. These ICs range in sophistication
(and price) from simple step-down or step-up
voltage regulators to much more sophisticated
chips with built-in rectifiers or maximum power
point tracking (MPPT).
What is maximum power point tracking?
It’s a complex topic, with significant research
continuing across industry and academia.
The problem is that the efficiency of power
harvesting of any source is affected by the
environment (i.e., amount of sunlight, device
temperature) and the load (i.e., how much
power is being drawn). An MPPT tries to
dynamically change the load that the harvester
sees, so that the maximum power is extracted.
This is extraordinarily hard to do well!
One of the more common (and older) of these
chips is the Texas Instruments BQ25504 (ti.
com/product/BQ25504), available on various
breakout boards. It has a built-in MPPT, buck-
boost regulator, and in some variants, internal
circuitry to manage the recharging of a battery
or a supercapacitor. Linear Technologies
LTC3588 (found on SparkFun’s breakout,
sparkfun.com/products/9946) has also been
around for a while (Figure
J
). It combines a
rectifier circuit and a buck converter to harvest
piezoelectric or solar sources that produce a
high voltage (10V–40V) and low current.
Some exciting directions are being explored
by startups who are tackling the unique
constraints of mobile devices and ultra-low-
power systems. For example, newer harvesting
ICs like the Nowi Energy NH2D0245
(Figure
K
)
optimize for higher MPPT efficiency and conduct
a much faster calculation of the maximum
power point, which means they can harvest
more energy in dynamic environments, for
example, on a wristwatch. You can buy the bare
chip from Digi-Key or request a breakout board
at nowi-energy.com/evaluation-boards.
Other startups are fine-tuning chips
for emerging harvesting sources. Matrix
Industries’ Mercury boost converters, available
from Digi-Key and Mouser, are custom-built
to harvest energy from tiny thermoelectric
generators (TEGs), aka Seebeck generators,
which generate an electrical current based on
the difference in temperature on the top and
bottom of the TEG. These have notoriously low
output voltages, which have to be boosted to
be of any use. Matrix’s Prometheus modules
(matrixindustries.com/prometheus) are
designed to harvest from thermoelectric
sources even at insanely low voltages (6mV).
The emergence of these custom chips, many
available for makers and hobbyists in nicely
designed breakout boards, make it an exciting
time to be making energy harvesting projects!
—Josiah David Hester
DEDICATED ENERGY HARVESTING CHIPS
J K
SparkFun; Nowi Energy
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