Looking around the world, engineers are providing innovative and innovative ways to harness non-traditional energy sources to solve real-world problems. Increased safety and accessibility, lower maintenance costs, improved energy efficiency, and system flexibility are just a few of the many benefits that can be gained with "acquisition" energy, wireless detection and monitoring/control systems. The high cost of energy, new government regulations, and environmental issues have led to a significant increase in demand for increased power efficiency in a variety of settings. Emerging alternative energy technologies and improved power utilization have the potential to achieve performance breakthroughs in many different markets. In addition, new products that take advantage of these new technologies mean excellent growth opportunities, both in the short and long term.
Many low-power industrial sensors and controllers are gradually shifting to alternative energy sources as the primary or auxiliary means of power supply. The ideal situation is that this collection of energy will completely eliminate the need to add a line power or battery. Transducers that generate power using off-the-shelf physical power sources (eg, thermoelectric devices [thermoelectric generators or thermopiles], mechanical vibrations [piezoelectric or electromechanical devices], and optical [photovoltaic devices]) are becoming the power source for many applications. Numerous wireless sensors, remote monitors, and other low-power applications are evolving into near-zero power devices that use only harvested energy (some often referred to as "nano-power").
Although “energy harvesting†appeared since the beginning of 2000 (at the time of its germination), it was only through the recent technological development that it was pushed to the commercial stage. In short, in 2010 we will usher in its “growth†stage. Building automation sensor applications using energy harvesting technology have been promoted in Europe, suggesting that its growth phase may have kicked off.
Existing applications confirm commercial viabilityAlthough the concept of energy harvesting has been widely known for many years, implementing a system in a real-world environment is cumbersome, complicated, and expensive. However, market examples using energy harvesting methods include transportation infrastructure, wireless medical equipment, tire pressure testing, and building automation. In the case of building automation, systems such as occupancy sensors, thermostats, and optical switches can eliminate the power or control circuitry typically required and replace them with a mechanical or energy harvesting system. In addition to eliminating the need for first line installations (or periodic battery replacement in wireless applications), this alternative can also reduce the routine maintenance costs often associated with wired systems.
Similarly, wireless networks using energy harvesting technology can connect any number of sensors in a building to reduce heating, ventilation, and air conditioning (HVAC) by cutting off power in non-critical areas when no one is inside the building. And lighting costs. In addition, the cost of energy harvesting electronics is often lower than the operating cost of the test line. Therefore, the use of energy harvesting technology can obviously bring economic benefits.
A typical energy harvesting configuration or system (represented by the four main circuit system modules shown in Figure 1 below) typically includes a free energy source, such as a thermoelectric connection to a heat source such as a HVAC pipeline. (TEG) or thermopile. These small thermoelectric devices convert small temperature differences into electrical energy. This electrical energy can then be converted by an energy harvesting circuit (the second module in Figure 1) and changed to a usable form for powering the downstream circuitry. These downstream electronics will typically include some type of sensor, analog to digital converter, and an ultra low power microcontroller (the third module in Figure 1). The above components can acquire the collected energy (now in the form of current) and wake up a sensor to obtain a reading or measurement, and then make the data available through an ultra low power wireless transceiver (in the circuit chain shown in Figure 1) The fourth module to represent) is transmitted.
Figure 1: Four main modules of a typical energy harvesting system
Each of the circuit system modules in the link (which may be an exception to the energy itself) has a unique set of constraints that have so far impaired its commercial viability. Low-cost and low-power sensors and microcontrollers have been around for quite some time; however, ultra-low-power transceivers have only just been commercialized in the past few years. However, the backwards state of the link has been the energy harvester and power manager.
The existing power manager module implementation is a low performance discrete architecture that typically includes 35 or more components. This type of design has low conversion efficiency and high quiescent current. These two deficiencies lead to performance loss in the end system. Low conversion efficiency will increase the time required for the system to power up, which in turn extends the time interval from when a sensor reading is taken to when the data is transmitted. High quiescent current limits the extent to which the energy harvesting power supply can be low because it must first exceed the current level required for operation before any remaining energy can be used to power the output. Finally, it requires a very high level of analog switch mode power expertise, and there is a shortage of people with this expertise!
The "missing link" (which you have to say) is always a highly integrated DC/DC converter capable of collecting and managing the remaining energy from very low input supply voltages. However, this situation is about to change.
Missing ringLinear Technology recently introduced its LTC3108, an ultra-low voltage boost converter and power manager designed to greatly simplify acquisition and management of power supplies from very low input voltages (eg thermopile, thermoelectric generator) [TEG], even small solar cells) are designed for the task of remaining energy. Its boost topology operates at input voltages as low as 20mV. This is important because it allows the LTC3108 to collect energy from a TEG with a temperature variation as small as 1 °C – in contrast to the high quiescent current due to the discrete implementation, it is quite desirable to do so. Hard work.
The circuit shown in Figure 2 uses a small step-up transformer for boosting the input voltage to an LTC3108, providing a complete power management solution for wireless detection and data acquisition. It captures small temperature differences and generates system power without the traditional battery power.
Figure 2: The LTC3108 used in wireless remote sensor applications is powered from a TEG (PelTIer Cell)
The LTC3108 utilizes a depletion-mode N-channel MOSFET switch to form a resonant boost oscillator (using an external step-up transformer and a small coupling capacitor). This allows it to raise an input voltage as low as 20mV to a high enough level to provide multiple regulated output voltages for powering other circuits. The frequency of the oscillation is determined by the inductance of the secondary winding of the transformer, typically in the range of 20 kHz to 200 kHz.
For input voltages as low as 20mV, a primary-secondary turns ratio of approximately 1:100 is recommended. For higher input voltages, a lower turns ratio can be used. These transformers are standard, commercially available components and can be ordered from magnetic component suppliers at any time. The 20mV low voltage operation is achieved with our composite depletion N-channel MOSFET.
As you can see from Figure 3, the LTC3108 takes a "system-level" approach to solving complex problems. It converts low voltage power and manages the energy between multiple outputs. The AC voltage generated across the secondary winding of the transformer is boosted and rectified using an external charge pump capacitor (connected between the secondary winding and pin C1) and a rectifier inside the LTC3108. The rectifier circuit feeds current into the VAUX pin and delivers the charge to the external VAUX capacitor and then to the other outputs.
The internal 2.2V LDO can support a low power processor or other low power IC. The LDO is powered by the higher of the VAUX and VOUT. This allows it to enter the operating state as soon as the VAUX is charged to 2.3V (when the VOUT storage capacitor is still in the charging process). If there is a step load on the LDO output, the current can take the autonomous VOUT capacitor if VAUX falls below VOUT. The LDO output is capable of delivering up to 3mA.
Figure 3: LTC3108 block diagram
The main output voltage on VOUT is charged from the VAUX supply and can be set by the user to one of four regulated output voltages using voltage select pins VS1 and VS2. The four fixed output voltages are: 2.35V (for supercapacitors), 3.3V (for standard capacitors), 4.1V (for lithium-ion battery terminals) or 5V (for higher energy storage) and a main system Power rail (used to power a wireless transmitter or sensor) - eliminating the need to add external resistors with resistances up to several megaohms (MΩ). Therefore, unlike discrete designs that require very large value resistors, the LTC3108 does not require special board coatings to minimize leakage.
The second output (VOUT2) can be turned on and off by the main microprocessor using the VOUT2_EN pin. When enabled, VOUT2 is coupled to VOUT through a P-channel MOSFET switch. This output can be used to power an external circuit such as a sensor or amplifier that does not have a low-power sleep or shutdown function. Powering up and powering down a MOSFET as part of the built-in detection circuitry of the building's thermostat is one such example.
VSTORE capacitors can have very large capacitance values ​​(several thousand μF or even F) to provide a hold when it is possible to lose input power. Once the power up operation is complete, the main output, alternate output, and switch output can be used. If the input power fails, the operation can still be sustained by the power supply of the VSTORE capacitor. The VSTORE output can be used to charge a large storage capacitor or rechargeable battery after VOUT has reached regulation. After VOUT reaches regulation, the VSTORE output will be allowed to charge up to VAUX (this voltage is clamped at 5.3V). The electrical energy storage components on the VSTORE can be used to power the system not only when the input power is lost, but also to supplement the current required for the VOUT1, VOUT2, and LDO outputs when the input power has insufficient energy.
A power good comparator is responsible for monitoring the VOUT voltage. Once VOUT is charged to within 7% of its regulated voltage, the PGOOD output will go high. If VOUT drops more than 9% from its regulated voltage, PGOOD will go low. The PGOOD output is designed to drive a microprocessor or other chip I/O and is not intended to drive higher current loads such as LEDs.
in conclusionIn summary, the LTC3108 thermal harvesting, DC-DC boost converter and system manager is a revolutionary device that can harvest energy from solar cells, thermoelectric generators or other similar heat sources. The device's unique resonant power converter topology enables it to start at very low input voltages of 20mV. Among the solutions currently available on the market for a complete energy harvesting chain, its high level of integration (including power management controllers and commercially available external components) makes it the smallest, most simple and easy to use solution. One.
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