[Shishuo Core Products] Can common traditional power supplies still compete in the era of intelligent edge?

The field of industrial sensor power supply is currently full of innovations, but it is also full of challenges. The implementation of intelligent edge requires preparation of intelligent data. This requires innovation in power supplies. In some cases, smart edge sensors need to be powered by a single twisted pair cable, and a Single Pair Power over Ethernet (SPoE) solution can meet the need. In other applications, nanoamp power solutions help save energy, enabling longer battery runtime on the sensor side. Additionally, some smart sensors require ultra-low noise power supplies so that sensor data is not affected. Finally, adding sensor intelligence at the edge will require the use of higher power density power supplies. This is because the new sensor needs to fit into the existing form factor.

In industrial systems, the intelligent edge can refer to sensors that independently select and process data. The amount of data transferred between the sensors and the central control unit is smaller, so data transmission is less difficult. Of course, to process the data provided by the sensors, a microcontroller is required. A simple example is an optical sensor used to detect specific information. For example, it can detect people who accidentally step into automated manufacturing areas, putting themselves at risk. When processing image data, it is important to ensure that people can be identified accurately so that a quick response can be made to shut down the machine. This should help prevent injury. The goal is to process image data at the intelligent edge. Only one signal (i.e., the person detected in the camera's field of view) is transmitted to the central computer. There is no longer a need to transfer image data to a central computer. Therefore, the required transmission bandwidth is lower and transmission is simplified.

By adding a processing unit (microcontroller) at the intelligent edge, a smart sensor can be created. However, the current consumption of this unit is high. In order to provide the higher currents required by the sensors, new power supply concepts are needed. This is especially true for existing industrial plants and infrastructure. In addition to enabling secure data transmission, the solution should also be able to easily and safely cope with the higher current requirements.

SPoE can be used as a power source via a 2-wire cable, thus helping to enable smart edges. SPoE is similar to Power over Ethernet (PoE), but can be implemented using existing 2-wire cables such as 4 mA to 20 mA interfaces. SPoE can transmit up to 52 W up to 400 meters, or up to 20 W up to 1 kilometer. SPoE is specified in the IEEE 802.3cg standard. The operating voltage of the line is 24 V or 55 V. A special feature of this power supply is that energy transmission and data transmission can take place on the same 2-wire cable. Data communication is based on the 10BASE-T1L standard. Figure 1 shows SPoE delivering up to 52 W over a 1 km long 2-wire cable.

In the smart edge application scenario, an example of low-power sensors in industrial environments are vibration sensors that are distributed in processing plants to monitor each machine.

The recorded vibrations correspond to different frequencies, providing an indication as to whether the machine's bearings and shafts are still operating reliably. Early signs of aging can be recognized. In this way, the likelihood of unplanned asset downtime or exceeding specific operating tolerances is reduced. Precise measurements of vibrations make this response possible. Vibration data monitoring requires complex algorithms to evaluate large amounts of data in real time. Data processing can occur locally at the deployment location or at a central location. With centralized evaluation, all collected sensor data must be transmitted via cables or wirelessly via radio waves.

In many applications it is advantageous to implement data evaluation locally directly on the sensor. For such an implementation, existing industrial plants can simply be equipped with vibration sensors without laying additional cables. If the sensor detects a frequency range outside the tolerance, it emits a prescribed warning signal.

Such sensors can be magnetically attached to machines or equipment and often form a mesh network that transmits data via radio waves. In this mesh network, various sensors communicate with each other and transmit information about which bearings show obvious signs of aging. Therefore, industrial plants can easily be equipped with predictive maintenance capabilities. ADI's OtoSense™ Smart Motor Sensor (SMS) technology is one example. It is a complete hardware and software solution for condition monitoring based on artificial intelligence technology. ADI OtoSense SMS monitors motor condition by combining advanced detection technology with leading data analytics.

An important prerequisite for the proper functioning of the system is the appropriate power supply for the sensor. The vibration sensor must not only have an appropriate power supply for the sensor itself, but also for the operation of the local microprocessor for evaluating the data and the RF module for wireless communication. The design of the sensor system helps to keep the current consumption as low as possible. It can use batteries as an energy source, or use energy harvesting. These two technologies are often used together. Adding energy harvesting extends the battery life so that the battery does not have to be replaced as often. A variety of energy sources can be used for energy harvesting. Depending on the location of the sensor, solar cells, thermoelectric generators (TEGs) or piezoelectric converters can be used. Especially in industrial production equipment, there are often temperature gradients that can be converted into electrical energy by TEGs. With the help of piezoelectric sensors, mechanical movements can also be converted into electrical energy.

For devices powered by methods such as batteries and energy harvesting, optimizing voltage conversion is important. High efficiency is key. There are several different nanoamp power management integrated circuits suitable for this purpose.

Figure 2 shows an example of a voltage conversion circuit using the MAX38650. It is a 100 mA nanoamp power step-down switching regulator. It can operate with supply voltages up to 5.5 V on the input side and provides a regulated output voltage between 1.2 V and 5 V. During operation, the switching regulator itself draws only 390 nA (typ). This is very low quiescent current. When the switching regulator is off, it consumes only 5 nA. Sensor data is not acquired continuously and communication is only required when a fault occurs. This means the MAX38650 can frequently switch to power-saving mode to further save energy.

Every basic voltage conversion circuit typically has a feedback pin. To provide a regulated output voltage, a simple resistor divider is required. However, resistor dividers don't make much sense in energy-saving circuits. Depending on the specific resistor value, either the current flowing through the voltage divider is too high, resulting in high losses, or the resistor value is so high that the feedback node has a very high impedance. As a result, noise can couple into the feedback node and directly affect the regulation of the required voltage. Interference is a particularly acute problem in industrial plants. As shown in Figure 2, the MAX38650 has an RSEL pin. It works using a single resistor which sets the output voltage. When the MAX38650 is turned on, 200 µA briefly flows through this external resistor. The resulting voltage is used to set the required output voltage for the entire operating duration of the voltage converter. This is the best of both worlds: low leakage current during operation and an adjustable and robust output voltage.

Many sensors can measure very small signals. To prevent these signal distortions, a very low noise power supply must be used. Conducted and radiated interference sources are the main sources of noise. Conducted interference can be greatly reduced with the help of additional filter circuits on the input and output sides of a switched-mode power supply switching regulator, but with radiated signal sources the situation is not so simple. Good circuit board layout can prevent excessive interference radiation. Even so, there is still residual noise coupling in the system. This can only be reduced by good shielding (i.e. metal casing). However, the manufacture of such shields is not only time-consuming but also costly.

Switching regulators with Silent Switcher technology provide a very clever solution that can effectively reduce radiated interference. The pulsed current paths present in any switch-mode power supply are designed symmetrically so that the resulting magnetic fields cancel each other out to a large extent. This technology can significantly reduce radiated interference when combined with flip-chip technology, which eliminates bond wires in switching regulator ICs.

Radiated interference can be reduced by up to 40 dB. This is equivalent to reducing the radiation power to one ten thousandth of its original value.

Figure 3 shows the symmetrical design of Silent Switcher technology, with the simultaneously generated localized pulse current shown in green. Pulsed currents produce pulsed magnetic fields of different polarities, which mostly cancel each other out.

Silent Switcher technology has now reached its third generation. In this generation, the ultra-low noise linear regulators also feature special ultra-low noise technology to reduce interference in the low frequency range, specifically between 10 Hz and 100 kHz. This generation of Silent Switcher technology makes it possible to eliminate the need for a filtered linear regulator between the switch-mode power supply switching regulator and the sensitive load in many applications.

Some sensors need to be placed in very small spaces, especially when existing sensors should be replaced with modern smart edge sensors in the same location. Due to increased functionality, more electrical components are often required. Therefore, innovative ways to reduce physical size must be found.

An interesting example in the field of voltage conversion is single inductor multiple output (SIMO) technology, which enables the use of a single inductor to generate multiple different output voltages. This technology saves board space that would otherwise be occupied by multiple inductors.

Figure 4 shows an example of a simple SIMO regulator circuit providing two precisely regulated output voltages. Additional supply voltages can be easily generated. Only one inductor, L, is required.

SIMO technology can be implemented in such a way that a single inductor is used continuously for all individual output voltages. A certain amount of energy is placed in the inductor, which is then used to generate the voltage VOUT1. Afterwards, another specified amount of energy is placed in the inductor and used to generate voltage VOUT2. In this way, each voltage generated receives exactly the energy needed to keep it stable.

The innovations in the power supply sector described in this article all demonstrate how to provide ideal power supply solutions for modern industrial sensors. Sensors are getting smarter. The data they generate is already evaluated locally at the intelligent edge. Sensors are increasingly being used in industrial plants to help optimize processes and minimize downtime. To keep up with this trend, innovative power supply concepts such as energy harvesting are necessary.