IndusTry 4.0/sMArT FACTorIes
mechanical vibrations or strain, a piezoelectric device can be used to convert these into electrical energy. once the electrical energy has been
produced, it can then be converted by an energy harvesting circuit and modified into a suitable form to power the downstream electronics. Thus, a microprocessor can wake up a sensor to take a reading or measurement, which can then be manipulated by an analogue-to-digital converter (AdC) for transmission via an ultra low power wireless transceiver. of course, the energy provided by the energy
harvesting source depends on how long the source is in operation. Therefore, the primary metric for comparison of scavenged sources is power density, not energy density. energy harvesting is generally subject to low, variable, and unpredictable levels of available power so a hybrid structure that interfaces to the harvester and a secondary power reservoir is often used. The harvester, due to its unlimited energy supply and deficiency in power, is the energy source of the system. The secondary power reservoir, either a battery or a capacitor, yields higher output power but stores less energy, supplying power when required but otherwise regularly receiving charge from the harvester. Thus, in situations when there is no ambient energy from which to harvest power, the secondary power reservoir must be used to power the Wsn. successfully designing a completely
self-contained wireless sensor system requires readily available power-saving microcontrollers and transducers that consume minimal electrical energy from low energy environments. existing implementations of such energy harvester blocks are shown in Figure 1. These typically consist of low performing discrete configurations, usually comprising 30 components or more. such designs have low
conversion efficiency and high quiescent currents. These deficiencies result in compromised performance in an end system. since high quiescent current limit how low the
output of the energy-harvesting source can be, it must first overcome the current level needed for its own operation before it can supply any excess power to the output. This is where AdI’s Power by LinearTM (PbL) product offerings can bring a new level of performance and simplicity.
An EnErgy HArvEsting ExAmplE The LTC3109 is a highly integrated dc-to-dc converter and power manager. It can harvest and manage surplus energy from extremely
low input voltage sources such as TeGs, thermopiles, and even small solar cells. Its unique proprietary autopolarity topology allows it to operate from input sources as low as 30 mV, regardless of polarity. The circuit in Figure 2 uses two compact
step-up transformers to boost the input voltage source to the LTC3109, which then provides a complete power management solution for wireless sensing and data acquisition. It can harvest small temperature differences and generate system power instead of using traditional battery power. The ac voltage produced on the secondary
winding of each transformer is boosted and rectified using an external charge pump capacitor and the rectifiers internal to the LTC3109. This rectifier circuit feeds current into the VAuX pin, providing charge to the external VAuX capacitor and then the other outputs. The internal 2.2 V Ldo regulator can support a low power processor or other low power ICs.
ConClusion With analogue switch-mode power supply design expertise in short supply around the globe, it has been difficult to design effective energy harvesting systems for use in green buildings. one of the primary hurdles has been power management aspects associated with remote wireless sensing. nevertheless, products like the LTC3109 can extract energy from almost any thermal source, thereby enabling a system designer to use an energy harvested power source. This not only reduces the use of fossil fuels but helps to make a greener building environment for current and future generations.
Figure 2. An LTC3109 typical application schematic.
Analog Devices
www.analog.com
20 deCeMber/JAnuAry 2022 | FACTory&HAndLInGsoLuTIons
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