Modern technology based on energy harvesting solutions solves the problem of "perpetual motion machine"

In history, perpetual motion machines have been discussed and studied by people, but many people do not know what the meaning behind this is. In people's imagination, perpetual motion machines are mechanical devices that can move automatically and continuously, and can also lift heavy objects and do some meaningful things. In the 13th century, people tried to make such a mechanical device, but no one really made it until the 21st century. In the current era of rich scientific knowledge, people certainly understand that such a machine is impossible to make because it violates the law of conservation of energy and the laws of thermodynamics. However, today, with the empowerment of leading ambient energy harvesting technology, some electronic systems that look more like "perpetual motion machines" have been widely used in life or industry. This article uses three application cases of ADI's ambient energy harvesting technology to interpret the solution ideas of realizing "perpetual motion machines" based on modern technology of energy harvesting solutions.

One of the most common application scenarios for power grid data collection is a node monitoring system called a fault indicator. When a power line fault occurs, it detects and sends an alarm, allowing line workers to repair the faulty equipment in the shortest possible time. In the past, due to limited budgets and resources of power companies, faced with high cumulative procurement costs and a large amount of recurring maintenance work, it was often impossible to deploy more fault indicators in the huge power infrastructure.

Ambient Energy Harvesting Power Line Monitoring Solution Based on ADP5091

To solve the above problems, ADI has developed a new line sensor architecture to achieve effective environmental energy collection and manage multiple power supplies, and achieve more than 90% power conversion efficiency through optimized maximum power point tracking. In addition, low-power operational amplifiers with wide dynamic range and high slew rate support Rogowski coil architecture and minimize magnetic field interference with current measurement accuracy. The integrated ISM band transceiver performs RF communication and supports sensor network protocols. The main advantage of this solution is that it can efficiently collect electrical energy, requires less maintenance, and supports faster system startup, lower power consumption and smoother operation.

The core chip is ADP5091, which provides efficient conversion of limited harvested energy (ranging from 16 μW to 600 mW) with sub-μW operating losses. With the internal cold start circuit, the regulator can start at an input voltage as low as 380 mV. After a cold start, the regulator can operate normally within an input voltage range of 80 mV to 3.3 V. The additional 150mA regulated output can be programmed via an external resistor divider or VID pin. By detecting the input voltage, the control loop can limit the input voltage ripple to a fixed range, thereby maintaining a stable DC-DC boost conversion. In OCV dynamic detection mode and non-detection mode, the programmed regulation point of the input voltage allows the energy of the harvester to be extracted to the maximum extent.

The working principle of thermoelectric power generation is based on the Seebeck effect. The thermoelectric generator is usually composed of hundreds of N-type and P-type material column structures. From the circuit point of view, they increase the thermoelectric potential by connecting in series, and in terms of heat transfer, they increase the efficiency of thermal energy use by connecting in parallel. When there is a temperature difference between the two ends of the device, the thermal field drives the movement of carriers and forms a thermoelectric current in the loop to output power. Using the electrical energy generated by the temperature change in the system, it is possible to operate a system with low-power circuit design, especially low-power applications that cannot use batteries or power lines. Now, even human body heat can be used to power sensors in wearable devices.

Take ADI's highly integrated DC/DC converter LTC3108 as an example. It is very suitable for collecting and managing residual energy from extremely low input voltage power sources such as TEG, thermopiles and small solar cells. A 3cm×3cm TEG connected to the LTC3108 can generate a voltage of 3.3 volts. At a temperature difference of 10 degrees, it can generate about 60 microamperes of current and 200 microwatts of power. If it is used in wearable devices, the human body surface temperature may be 35 degrees. Even if the ambient temperature is 25 degrees, there can be a temperature difference of 10 degrees. A larger temperature difference can generate greater power, and it can continuously power wearable devices, achieving true "charging-free".

Applications of LTC3108 TEG Energy Harvesting Devices

A wireless power transfer (WPT) system consists of two parts separated by an air gap: the transmit (Tx) circuit (including the transmit coil) and the receive (Rx) circuit (including the receive coil). Much like a typical transformer system, the AC generated in the transmit coil generates AC in the receive coil through magnetic field induction. However, unlike a typical transformer system, the coupling between the primary (transmitter) and secondary (receiver) sides is usually low. This is due to the presence of a gap of non-magnetic material (air).

Most wireless power transfer applications today are in wireless battery charger configurations. However, if a particular application does not have a battery at all, but instead only needs to provide a regulated voltage rail when wireless power is available, examples of such applications are common in remote sensors, metering, automotive diagnostics, and medical diagnostics. If this remote sensor only needs to give a reading when the user is nearby, it can be wirelessly powered on demand.

The LTC3588-1 is a nanopower energy harvesting power solution optimized for high impedance sources such as piezoelectric sensors and suitable for energy harvesting in radio wave environments. It has a built-in low-loss full-wave bridge rectifier and a high-efficiency synchronous buck converter to transfer energy from an input storage device to the output to generate a stable voltage that can support up to 100mA load. The figure below shows a complete transmitter and receiver WPT solution using the LTC3588-1 (it is worth mentioning that the power supply distance of this solution is suitable for applications within 2mm).

WPT uses LTC3588-1 to provide a stable 3.3 V rail