LTC3107 for energy harvesting to extend the life of the main battery in low-power wireless systems

Background Information

Historically, various types of sensors have been conventionally connected to their respective power sources via wires. However, today there may be no challenges and costs of installing cables throughout the building or factory. It is now possible to install reliable and industrial-strength wireless sensors that can rely on small batteries to collect energy even from light, vibration or temperature changes. It has been running for many years. In addition, rechargeable batteries and a variety of environmental energy sources can be combined. Moreover, due to inherent safety issues, some rechargeable batteries are not likely to be charged by wires, but rather need to be charged by wireless power transfer technology.

 

The latest and off-the-shelf energy harvesting technology products (eg vibration energy harvesting products using piezoelectric transducers and indoor photovoltaic cells) produce milliwatts of power under typical operating conditions. Although this magnitude of power may initially seem limited, the multi-year operation of the collection component may mean that the energy harvesting product is roughly similar to the long-life primary battery, both in terms of energy supply and cost per unit of energy provided. . In addition, systems that use energy harvesting products are typically recharged after the battery is exhausted, a system that is powered by the main battery is not possible. Therefore, although the use of energy harvesting products to power the sensors adds cost, this can offset the maintenance costs of replacing the primary battery every 7 to 10 years.

  

Overcome obstacles

Wireless and wired sensor systems are often in an environment filled with environmental energy, which is ideal for powering the sensor itself. It is now generally accepted that energy harvesting can significantly extend the life of installed batteries, especially when power requirements are low, in addition to reducing long-term maintenance costs, and reducing downtime. Despite these benefits, there are still some obstacles to adoption. Most notably, environmental energy is often intermittent or insufficient to power the sensor system continuously, and the main battery power supply is extremely reliable over its specified lifetime. As a result, some system designers may be reluctant to upgrade their systems to collect environmental energy, especially when seamless integration is important.

 

However, most deployments use ambient energy as the primary power source, but use a battery as a supplement to the primary power source. If the ambient energy disappears or is interrupted, the primary battery can be accessed. This battery can be a rechargeable battery or not, and how it is selected is usually determined by the final application itself. Therefore, the inevitable conclusion that can be drawn is that if the final deployment allows very convenient replacement of non-rechargeable batteries, maintenance personnel can easily and cost-effectively replace, then the use of non-rechargeable batteries is economically significant. However, if replacing the battery is very cumbersome and costly, then using a rechargeable battery is more economical.

 

Even if you choose a rechargeable battery, there are still many problems with the best way to charge. The factors that influence the choice of charging method are:

1) Is there a wired power supply to charge the battery?

2) Can ambient energy provide sufficient power? There is sufficient power to power the wireless sensor network (WSN) and charge the battery.

3) Is wireless power transfer required to charge the battery due to the inherent security requirements due to the dangerous nature of the deployment environment?  

Regardless of the solution required for a specific energy harvesting deployment, there are many IC solutions that provide system designers with the necessary performance characteristics to simplify and easily meet the needs of their systems.

 

Simple and effective solution

 

Linear Technology's LTC3107 is a highly integrated DC/DC converter that extends power in low-power wireless systems by collecting and managing the remaining energy from very low input voltage sources such as TEG (thermoelectric generators) and thermopiles The life of the main battery.

 

With the LTC3107, the point-of-load energy harvester requires very little space, as long as it is large enough to accommodate the LTC3107 3mm x 3mm DFN package and several external components. By generating an output voltage that tracks the existing main battery voltage, the LTC3107 can be seamlessly used to provide free heat harvesting for new and existing battery-powered designs to reduce cost. In addition, the LTC3107, along with a small thermal energy source, extends battery life and, in some cases, long battery life on the shelf, thereby reducing maintenance costs associated with battery replacement and recurring costs. Depending on the load and the amount of energy available, the LTC3107 is used to boost the battery or even power the load independently.

 

Another example is the LTC3331, a complete energy harvesting conditioning solution that delivers up to 50mA of continuous output current to extend battery life when harvestable energy is available. When using the collected energy to provide stable power to the load, the device does not require a battery to supply current, and when battery powered under no load conditions, only 950nA of operating current is required. The LTC3331 integrates a high-voltage energy harvesting power supply and a synchronous buck-boost DC/DC converter powered by a rechargeable main battery to produce a single, non-interrupted output for energy harvesting applications such as wireless sensor nodes and IoT devices.

 

Figure 1: The LTC3331 converts multiple energy sources and uses a rechargeable main battery

The LTC3331's energy harvesting power supply consists of a full-wave bridge rectifier suitable for AC or DC input and a high efficiency synchronous buck converter that collects energy from piezoelectric (AC), solar (DC) or magnetic (AC) sources. The 10mA shunt uses a collection of energy to achieve simple battery charging, while the low battery disconnect feature protects the battery against deep discharge. The rechargeable battery powers the synchronous buck-boost converter operating from 1.8V to 5.5V input. It can be used when the collected energy is not available. The output can be adjusted regardless of the input above, below or equal to the output. LTC3331 Battery chargers have a very important power management feature that should not be overlooked when dealing with micropower supplies. The LTC3331 includes battery charger logic control so that the device will only charge the battery when there is excessive energy in the energy harvesting power supply. Without this logic function, the energy harvesting power supply will be stuck at some non-optimal operating point at startup, and the startup process cannot be completed, and the intended application cannot be powered. When the collected energy is no longer available, the LTC3331 automatically switches to the battery. This adds to the benefit that a battery-operated WSN can extend the operating life from 10 years to more than 20 years if a suitable energy harvesting power source is available for at least half of the time, if the collection of energy is more common, even Extend to a longer time. The device also integrates a supercapacitor balancer to increase output energy storage.

 

in conclusion

To facilitate the use of environmental energy harvesting technology in a variety of new and existing main battery powered applications, Linear Technology has introduced energy harvesting ICs for different battery voltage applications. This includes most popular long-life primary batteries used in lower power applications, such as 3V coin-shaped lithium batteries and 3.6V lithium thionyl chloride batteries. These products easily provide the best of both worlds, with the reliability of battery power, maintenance cost savings in energy harvesting, and minimal design effort.