What is Diode Biasing?

PCB assemblies often contain numerous components. The engineer designing the board selects these components individually, based on their function in the circuit. For a successful project, it is essential to understand the basic operation of these components individually, and in relation to one another. One such component is the diode.

A diode is a semiconductor device with a PN junction. It supports current flow in only the forward direction—from the anode to the cathode—and not in the reverse. However, to allow current flow in the forward direction, a diode must be given a particular voltage to overcome the bias in its PN junction. Diode biasing is the application of a DC voltage across the diode’s terminals for overcoming the PN junction bias.

It is possible to bias a diode in two ways—forward and reverse. When forward biased, the diode allows current flow from its anode to its cathode, provided the biasing voltage is greater than the PN junction bias. However, when reverse-biased, the biasing voltage cannot overcome the PN junction bias, and the diode blocks any current flow. Reverse biasing a diode is a convenient way for using it to convert alternating current to direct current. Proper use of forward and reverse biasing also allows other functions, such as electronic signal control.

Diodes are mostly germanium or silicon-based. A diode consists of a layer of P-type semiconductor material and another layer of an N-type semiconductor material joined together. The P-type material forms the anode terminal and the N-type material forms the cathode terminal of the diode.

When fabricating a diode, the manufacturer dopes the two layers differently. They dope one of the layers with boron or aluminum to make it P-type, which gives it a slightly positive charge. The P-type semiconductor, therefore, has a deficit of electrons or an abundance of holes. They dope the other layer with phosphorus or arsenic to give it a slightly negative charge and make it N-type. Therefore, the N-type semiconductor has an abundance of electrons.

At the junction of the P-type and N-type layers, electrons and holes combine to form a sort of neutral zone. Therefore, when a current must flow, a voltage bias is necessary to push the electrons and holes through this neutral zone. The neutral zone is less than a millimeter in thickness.

A forward bias pushes holes from the P-type layer, across the neutral zone, into the N-type layer. The forward bias reduces the width of the neutral zone to allow the current to flow. The forward bias necessary depends on the material of the diode. It is 0.7 VDC for silicon diodes and about 0.3 VDC for germanium diodes.

On the other hand, a reverse bias adds more electrons to the N-type layer and holes to the P-type layer. This increases the width of the neutral zone, making it impossible for current to flow across it.

Therefore, forward biasing allows current flow through the diode from the anode to the cathode, and reverse biasing prevents current flow. Even with forward biasing, there is no current flow until the voltage is able to overcome the PN junction bias.

Parylene Conformal Coatings for Electronics

Conformal coating on electronic assemblies protects sensitive components and copper tracks on circuit boards from the vagaries of the environment. Typical conformal coatings are epoxy-based, requiring a thick layer to be effective. Parylene conformal coatings, on the other hand, can be ultra-thin and pinhole-free as they are polymer based.

Parylene conformal coatings offer a number of high-value surface treatment properties. These include resistance to moisture and chemical ingress and an effective dielectric barrier. In addition, Parylene also offers excellent thermal conductivity, dry-film lubricity, and UV stability, very essential for electronic subsystems. These properties of Parylene conformal coatings make it an ideal choice for various applications in the fields of consumer electronics, medical electronics, transportation industry, and defense and aerospace industries.

Manufacturers of a unique polymer series use the generic name Parylene for their products. These variations or members of the Parylene family each offer their own, somewhat different properties of the coating. Parylene variants are commercially available, and they are Parylene N, C, D, HT, and ParyFree.

Parylene N or poly(para-xylene) is the basic member of the series. This is a totally linear and highly crystalline material. Being a primary dielectric, Parylene N exhibits a very low dissipation factor and high dielectric strength. It shows an exceptionally low dielectric constant, varying very little with frequency. It also exhibits substantially high crevice-penetrating ability, second only to Parylene HT.

The second commercially available member of the Parylene series is Parylene C, derived from the same raw material as Parylene N. The only difference from Parylene N is the substitution of a chlorine atom for an aromatic hydrogen atom. The useful combination of physical and electrical properties, in addition to very low permeability to corrosive gases and moisture, makes Parylene C useful as a conformal coating.

The third member of the Parylene series is Parylene D, also a derivative of the same raw material that produces Parylene N. The substitution of a chlorine atom for two aromatic hydrogen atoms differentiates Parylene D from Parylene N. Most properties of Parylene D are similar to those of Parylene C. However, Parylene D has the added ability for withstanding slightly higher use temperatures.

The newest addition to the Parylene family is Parylene HT, a commercially available variant. The difference from the other family members is in the replacement of the alpha hydrogen atom of the N dimer with fluorine. Parylene HT can withstand temperatures of 450 ℃, therefore suitable for high-temperature applications. It also has excellent long-term UV stability, a low coefficient of friction, and low dielectric constant. Among the four of the family above, Parylene HT shows the highest penetrating ability.

A unique member of the family series is ParyFree, and this is also the newest. The difference from Parylene N dimer is in the replacement of one or more hydrogen atoms with a non-halogenated substituent. Compared to other commercially available Parylenes, this halogen-free variant offers advanced barrier properties of Parylene C along with substantially improved mechanical and electrical properties. This allows ParyFree to offer robust protection against water, moisture, corrosive solvents, and gasses, as required by select industries.

Robots with Eyes and Brain

In the manufacturing industry, a huge transformation is taking place—machine vision—and it is growing at astronomical proportions. This includes all types of machine vision. For instance, the market is expecting 3D machine vision to double in size during the coming six years. As of now, this technology is proving to be a vital component in many modern solutions for automation.

Several factors contribute to the increasing adoption of this technology in manufacturing. While there is greater demand for automation solutions as the industry grapples with labor shortages, the cost of automation has decreased tremendously—sensors, cameras, robotics, and processing power are now substantially cheaper—enabling greater deployment.

Technological performance has also jumped up a notch higher, and machine vision systems now have the ability to process substantial amounts of information within a fraction of a second. Finally, machine learning algorithms and advanced artificial intelligence are transforming the data collected by machine vision even more versatile, allowing manufacturers to better realize the power from those solutions. Incorporated into automation solutions, machine vision is now producing better outcomes.

The vision system of a machine is basically made up of a number of disparate parts. These include the camera, lenses, sources of lighting, robotic movements, processing computers, application-specific software, and artificial intelligence algorithms.

While the camera forms the eyes of the system, machine vision can have several types of cameras depending on the application’s needs. An automated solution may have various cameras with different configurations.

For instance, there can be static cameras, for placing in fixed positions. These usually have a more bird’s eye view of the process, useful in applications where speed is imperative. On the other hand, dynamic cameras placed on the end of robotic arms can come much closer to the process, resulting in much higher accuracy and detailed capture.

Another important aspect of the vision system is its computing power. This is the brain of the system that helps the eyes (cameras) to do their work. Computation resources, coupled with machine learning algorithms, must not be confused with traditional machine vision applications. Companies offering machine vision capability also offer software libraries for implementation.

While manufacturers design their systems specifically for application users, others offer them targeted toward software programmers. Ultimately, the software provides the machine vision system with advanced capabilities offering a dramatic impact for manufacturers. Programs are available for control of tasks along with the ability to provide feedback from the line with valuable insights.

Machine vision-guided systems are gaining steam as a concept for replacing basic human capabilities. For instance, machine vision for assembly lines enables an increasing range of processes and applications.

Typical applications of machine vision include assembly processes for power tools, medical equipment, home appliances, and industrial assembly lines. Most assembly steps in the fabrication of electronic equipment can benefit from the use of machine vision, as it offers a substantial increase in the level of precision achieved.

For instance, machine vision improves inspection of component placement of tiny surface mount components on printed circuit boards before they go for soldering. It improves the line throughput, while not succumbing to fatigue as a human inspector would.

3D Printing and Electricity from Waste Heat

There are several techniques existing for recovering energy from waste heat. The typical approach is to use waste heat to generate electricity. Now 3-D printing methods are taking the lead to make devices that will convert waste heat into electricity.

UNIST is located in the largest industrial city of Ulsan in Korea. Engineers there have conducted breakthrough research. They have developed a new thermoelectric technology for producing power-generating tubes. The best part of their research is they can print the tubes using 3-D printing methods.

Most automobile and industrial exhaust gases generally go to waste. But they are usually hot. By generating electricity from these hot exhaust gases, it is possible to enhance the efficiency of fossil energy production techniques. For this, the most suitable method is to use thermoelectric or TE methods. However, this is not an easy task, as typical thermoelectric products that the traditional processes produce are neither cost-effective nor do they fulfill efficiency requirements. According to the researchers, exhaust pipes fall into this category.

Engineers addressed this inefficiency issue by creating a special type of exhaust pipe. They built it out of lead and tellurium and used 3-D printing techniques for creating it. According to the researchers, they created the ink for the 3-D printer by mixing metal particles with a glycerol solvent. This provided them with the necessary viscoelasticity necessary for the ink and gave the ink the necessary characteristics of elasticity and viscosity.

The tube printed with this ink offers a high thermoelectric performance between temperatures of 400 and 800 °C. Most exhaust gases from vehicles exhibit this range of temperatures.

The research was a joint venture between the Department of Mechanical Engineering, UNIST, and the Department of Materials Science and Engineering, UNIST.

With their computational and experimental findings, the researchers have demonstrated the efficacy of their 3-D printed TE tubes they made from PbTe for power generation from waste heat. Their design has proven to be a system-adaptive and high-performance thermoelectric generator.

The 3-D printed power-generating PbTe TE tubes are made of p-type material and n-type material, with insulating material separating them. The TE tube has a series of p-type PbTe tubes followed by an insulating tube, and an n-type tube repeating many times. One complete power-generating TE tube may have ten pairs of p-type and n-type PbTe tubes in series.

According to the lead researcher, this 3-D printed power-generating PbTe TE tube technology can efficiently convert waste heat escaping through factory chimneys into electricity. In fact, factory chimneys are the most common type of source of waste heat. The shape of the tube makes it very effective for collecting heat as compared to the conventional rectangular shape of present TE generators.

Using 3-D printing technology for producing thermoelectric materials overcomes the limitations that engineers typically face while using commercial materials. According to the researchers, other fields can also use the viscoelastic characteristics that 3-D printed materials offer. The publication Advanced Energy Material features this novel and innovative research in thermoelectric materials.

Nanomaterial for Improving LED Brightness and Efficiency

LEDs are a ubiquitous presence in our lives. They have replaced almost all forms of lighting devices we were using earlier, replacing incandescent lamps, fluorescent lamps, compact fluorescent lamps, mercury vapor lamps, and sodium vapor lamps. This has been possible primarily because of the efficiency and long life of LED lamps. Now there is new research to suggest ways to improve their efficiency and brightness further. This could lower their cost, leading to a further lowering of the cost of scientific tools and consumer goods.

A huge team of researchers, including engineers from the Academia Sinica in Taiwan, the SLAC National Accelerator Lab, Brookhaven, National Laboratory, Los Alamos, and the Center of Nanoscale Materials, Argonne, have managed to make stabilized perovskite nanocrystals. They will use these nanocrystals in LEDs to improve their brightness and stability substantially.

Perovskite crystals have a singular crystalline structure, giving them properties for absorbing and emitting light. This characteristic is helpful in making energy-efficient devices including gamma detectors, consumer devices, and solar cells.

Although scientists have long considered perovskite nanocrystals as a prime candidate material for LEDs, the unstable nature of the perovskites prevented them from actual implementation. The research team stabilized the crystals by embedding them in a porous structure of MOF or a framework of metal and organic substances.

Such an intriguing concept of stabilization has been accomplished earlier also. But scientists could demonstrate that only in powder form. Earlier attempts to create LEDs from perovskite nanocrystals failed as the nanocrystals degraded back to their bulk phase. This led to a loss of their nanocrystal advantages in building LEDs. In the bulk form, the perovskite is in the nanophase, and it behaves differently.

The team managed to solve the problem by creating the perovskite crystals in the emission layer in an LED, for the first time. They have demonstrated that it is possible to manufacture light-emitting diodes at a low cost with perovskite nanocrystals by embedding them in a framework of metal and organic substances. Embedding the perovskite nanocrystals in a MOF framework stabilizes them for the working conditions of the LED.

For making the MOF, the team used a framework of lead nodes as the metal precursor, and for the organic material, they used halide salts. The methylammonium bromide in the halide salts reacted with the lead in the framework, forming nanocrystals around the lead core, and trapping them in the matrix.

As the matrix isolates the nanocrystals, they cannot interact and degrade. The researchers used this method as a coating, as it is substantially cheaper than vacuum processing. Almost all inorganic LEDs in wide use today require vacuum processing.

The team claims it is possible to create bright red, green, and blue LEDs with the MOF-stabilized technique. According to them, it is also possible to create them in various shades of the three colors. They have demonstrated, for the first time, that by stabilizing perovskite nanocrystals in MOF, they can create bright and stable LEDs in a full range of colors. It is possible to create LEDs of different colors, and improve their color purity while enhancing their ability to generate light.

3-D Printed Electronics

Today, 3-D printing is the most popular technology among all manufacturing and prototyping methods. However, 3-D printing is not new. In the 1980s, a company filed a patent for 3-D constructing models using stereolithography. Such patents have been instrumental in holding back the development, manufacture, and distribution of 3-D printing technology, until now.

3-D printing typically works by slicing a 3-D design into several small horizontal 2-D sections and then splicing them together by printing each 2-D slice atop the other. 3-D printers commonly use a thermoplastic wire wound on a reel. The printer extrudes this wire through a hot nozzle. There are 3-D printers that build models from paper. They cut out each layer from the paper, and glue one layer to the next. Other, more advanced systems sinter metallic dust using lasers.

It is possible to use 3-D printing technology for manufacturing electronic components. This uses a printer and an additive process. However, not all see the 20-D printed electronics as being actually 3-D printed. For instance, although they consider transistors as 2-D, in actual practice, they are 3-D, requiring both additive and subtractive processes to build up their insulating layers, source and gate terminals.

For now, there is little practical application for most 3-D printed electronics, and their use in the real world is rare. This is so because manufacturing electronics in the traditional manner is much easier, cheaper, and more reliable. Still, there is a significant amount of research for trying and creating practical devices with 3-D printing technology. So far, there has been significant success in printing transistors, capacitors, diodes, and resistors using 3-D processes.

Although electronic components may use several materials, 3-D printed devices generally use graphene or other organic polymers. Researchers use graphene, as it gives them the ability to create narrow channels and gates while allowing doping. It is easy to dispense organic polymers in solution form, which is ideal for using them in inkjet printers.

However, with printed electronic capabilities still far removed from standard electronic systems, it is rare to find commercial applications for printed electronics. However, there is plenty of research going into printing them.

Being still in their infancy, printed electronics are presently found only in research labs, or in prototypes. There are two technologies popular, tending towards practical—Pragmatic and Duke University.

A UK-based company, Pragmatic, produces printed electronic components for one-time applications. These are disposable electronic items like RFID tags. The most significant feature of Pragmatic devices is they use a flexible substrate. They cover all essential components like resistors, capacitors, and transistors. Although Pragmatic has not fully demonstrated a functional device, they have produced ARM core processes, claiming each device consumes 21 mW and energy efficiency of 1%.

Presenting the best examples of practical printed electronics, Duke University claims its products exceed the typical life cycle. They use a new method of additive processes for creating printed electronic components like resistors, capacitors, and transistors. Their components are mostly based on carbon, while the construction uses aerosol spraying similar to inkjet technology. They build the insulating layers from cellulose.

Modern Smoke Safety Sensors

The CN-0537 is a modern smoke detector with a design complying with the specifications outlined in UL 217. The design is based on fire data that researchers have collected at the smoke testing facilities of the Underwriters Laboratories and Intertek Group plc. The design uses the integrated optical sensor ADPD188BI and an optimized smoke chamber. It has a single calibrated device for sensing and measuring smoke particles. 

The design also uses a smoke detection algorithm that UL has tested and verified. This facilitates OEMs in reducing their product development time and thereby delivering their product designs more quickly.  The hardware design has a form factor resembling the Arduino board, and this includes an ADICUP3029 microcontroller development board apart from the CN-0537 smoke detector.

There are two basic designs popular for smoke detectors. One is the ionization type which uses radioactive materials to ionize the air while checking for electrical imbalances. The other is the photoelectric type that checks for current in the photodetector caused by light reflecting off airborne smoke particles and falling on the photodiode.

Although experts recommend a combined solution of both types, the improved reliability of the photoelectric smoke detector makes it more popular. It is faster in detecting common house fires and has a smaller response time to smoldering fires.

The optical module ADPD188BI is a complete photometric system. Its design is specifically meant for smoke detection applications. Rather than the conventional discrete smoke detector circuits, using the ADPD188BI makes the design significantly simpler. This is because the integrated package contains two LEDs and two photodiodes, along with an analog front end. The module utilizes a double-wavelength technique. The two LEDs emit light at different wavelengths—blue light at 470 nm, and infrared light at 850 nm. The LEDs also pulse at two independent time slots, and any particulate matter present in the air scatters the transmitted light back into the device.

The scattered light reaches two integrated photodiodes, which produce proportional levels of current. The analog front electronics digitize this output current. As the optical power from the LEDs is maintained constant, any increase in the ADPD188BI output over time indicates that airborne particles are building up.

The response of the ADPD188BI photometric sensor is a ratio of the input optical power to the transmitted optical power. The manufacturers refer to this as the power transfer ratio or PTR and express it as nW/mW. PTR is a more meaningful parameter than the raw output, as it is independent of the actual hardware settings.

The ambient temperature affects the response of the ADPD188BI system. As the shape of the temperature response curve can vary for the blue LED depending on the amount of current in the LED, it complicates matters further. The temperature response curve of the infrared LED is independent of the LED current.

The CN-0537 smoke detector has a temperature and humidity sensor that monitors the conditions, in real-time, within the chamber right next to the optical module ADPD188BI. This helps to determine the value of the relative response. The software helps with temperature compensation.

Protecting the Li-ion Battery

For decentralization of the source of energy, it is hard to beat rechargeable lithium-ion batteries. A wide range of applications uses this electrochemical option of energy storage as a strategic imperative. That includes powering up units in the military sector,  storing and providing energy for personal use, keeping uninterruptible power supply systems operational for data centers and hospitals, storing energy from photovoltaic systems, and enabling the operation of battery electric vehicles and power tools.

The rechargeable battery pack is the most common design in the accumulator segment and accounts for the major share of battery-powered applications. Such a pack usually consists of multiple Li-ion cells. With continuous technological development, the economics of the Li-ion rechargeable battery pack is also becoming attractive enough to warrant a substantial increase in its use. This is also leading to the miniaturization of individual cells, resulting in an increase in their energy density.

However, even with the increased availability and use, the Li-ion rechargeable battery pack continues to carry a residual risk of hazards, especially due to the increase in energy density brought on by miniaturization. The disadvantage is in terms of safety.

The electrolyte in the Li-ion cells is typically a mixture of organic solvents and a conductive salt that improves its electrical conductivity. Unfortunately, this also makes the mixture highly flammable. During operation, the presence of an inordinate thermal load can lead to the point where the mixture becomes explosive. Furthermore, this safety hazard to the end-user is increasing with the constant efforts to further increase the energy density of Li-ion cells.

Most electric battery cells have a narrow operational temperature range, varying from +15 °C to +45 °C. That makes temperature the key parameter. When the cell exceeds this temperature range, its rising heat becomes a threat to its functional safety, and to the safety of the overall system.

Overcharging the battery substantially increases the statistical probability of the defect in the cell. This may lead to a breakdown of the cell structure, typically associated with the generation of fire and in some cases, an explosion.

Manufacturers of rechargeable battery packs try to mitigate this risk by including a battery management system, and primary and secondary protection circuits that they embed in the electronic safety architecture of the battery. This allows the battery to remain within its specified operating range during the charging and discharging cycles. But nothing is immune to failure, including components in the protection circuit, and the battery system can ignite and explode on an excessively high load.

As the battery powers up a load, excessive current flow can heat up the battery, and the primary protection circuit may not detect it even when it exceeds the permissible level. For the protection of batteries, RUAG Ammotec is offering a heat lock element, a pyrotechnical switch-off device that is entirely independent of the battery system. This comprises a physicochemical sensor to continuously monitor the environmental heat. As the temperature rises, the sensor blocks the flow of current permanently. The heat lock element causes an insulating piston to shear off a current conductor, thereby electrically isolating the battery.

Are We Ready for 6G?

Apart from simply being an evolution of the 5G technology, 6G is actually a transformation of cellular technology. Just like 4G introduced us to the mobile Internet, and 5G helped to expand cellular communications beyond the customary cell phones, with 6G the world will be taken to newer heights of mobile communications, beyond the traditional devices and applications for cellular communication.

6G devices operate at sub-terahertz or sub-THz frequencies with wide bandwidths. That means 6G opens up the possibility of transfers of massive amounts of information compared to those under use by 4G and even 5G. Therefore, 6G frequencies and bandwidth will provide applications with immersive holograms with VR or Virtual Reality and AR or Augmented Reality.

However, working at sub-THz frequencies means newer research and understanding of material properties, antennas, and semiconductors, along with newer DSP or Digital Signal Processing technologies. Researchers are working with materials like SiGe or Silicon Germanium and InP or Indium Phosphide to develop highly integrated high-power devices. Many commercial entities, universities, and defense industries have been going ahead with research on using these compound semiconductor technologies for years. Their goal is to improve the upper limits of frequency and performance in areas like linearity and noise. It is essential for the industry to understand the system performance before they can commercialize these materials for use in 6G systems.

As the demand increases for higher data rates, the industry moves towards higher frequencies, because of the higher tranches of bandwidth availability. This has been a continuous trend across all generations of cellular technology. For instance, 5G has expanded into bands between 24 and 71 GHz. 6G research is also likely to take the same path. For instance, commercial systems are already using bands from FR2 or Frequency Range 2. The demand for high data rates is at the root of all this trend-setting.

6G devices working at sub-THz frequencies require generating adequate amounts of power for overcoming higher propagation losses and semiconductor limits. Their antenna design must integrate with both the receiver and the transmitter. The receiver design must offer the lowest possible noise figures. The entire available band must have high-fidelity modulation. Digital signal processing must be high-speed to accommodate high data rates in wide bandwidth swathes.

While focussing on the above aspects, it is also necessary to overcome the physical barriers of material properties while reducing noise in the system. This requires the development of newer technologies that not only work at high frequencies, but also provide digitization, test, and measurements at those frequencies. For instance, handling research at sub-THz systems requires wide bandwidth test instruments.

A 6G working system may require characterization of the channel through which its signals propagate. This is because the sub-THz region for 6G has novel frequency bands for effective communications. Such channel-sounding characterization is necessary to create a mathematical model of the radio channel that can encompass intercity reflectors such as buildings, cars, and people. This helps to design the rest of the transceiver technology. It also includes modulation and encoding schemes for forward error correction and overcoming channel variations.

Why are VFDs Popular?

The industrial space witnesses many innovations today. This is possible due to easily affordable and available semiconductors of various types, which makes it easier for manufacturers. One of the most popular innovations is the VFD or variable frequency drive.

Earlier, a prime mover had only a fixed speed, and its use was limited to expensive, non-efficient devices. With the advent of VFDs, it was possible to have an easy, efficient, cost-effective, and low-maintenance method of controlling the speed of the prime mover. This addition to the control of a prime mover not only increases the efficiency of the operation of equipment but also improves automation.

OEMs typically use VFDs for small and mobile equipment. They only need to plug it into a commercial single-phase outlet, in the absence of a three-phase power supply. These can be hose crimpers, mobile pumping units, lifts, fans/blowers, actuator-driven devices, or any other application that uses a motor as the prime mover. Using a VFD to vary the motor’s speed could improve the operation of the equipment. Apart from the benefits of variable speed, OEMs also use VFDs because of their ability to use the single-phase power source to output a three-phase supply to run the motor.

Although the above may not seem much, the value addition is tremendous, especially for the production of small-batch items. As VFDs output three-phase power, they can use standard three-phase induction motors, which are both widely available and cost-effective. VFDs also offer current control. This not only improves motor control but also helps in avoiding inrush currents that are typical when starting induction motors.

For instance, a standard duplex 120V 15A power source can safely operate a 0.75 HP motor without tripping. However, a VFD, when operating from the same power source, can comfortably operate a 1.5 HP motor. In such situations, using a VFD for doubling the prime mover power has obvious benefits for the capacity or functionality of the application.

The above benefits make VFDs an ideal method of controlling motors for small OEM applications. VFD manufacturers also recognize these benefits, and they are adding features to augment them. For instance, they are now adding configurable/additional inputs and outputs, basic logic controls, and integrated motion control programming platforms to VFDs. This is making VFDs an ideal platform for operating equipment and controlling the motor speed, thereby eliminating any requirement for onboard microcontrollers.

However, despite several benefits, VFDs also have some limitations. OEMs typically face problems when using GFCI or ground fault circuit interrupter breakers with VFDs. A GFCI typically monitors current flowing through the ground conductor. Leakage currents through the ground conductor can electrocute users.

A VFD consists of an inverter stage that works on high-frequencies. Harmonics from this stage can create ground currents, also known as common-mode noise. The three-phase waveforms generated by the inverter do not always sum to zero (as is the case in a regular three-phase power source), leading to a difference of potential causing capacitive induced currents. When these currents seek a path to the ground, they can trip a GFCI device. However, this can be minimized by lowering the operating frequency.