Space Saving Molex Connectors

With manufacturing processes and semiconductor materials going through new developments at break-neck speeds, we now have a proliferation of increasingly smaller sensors, devices, and processors. However, some areas are still facing hindrances in technological advancements because of space limitations, thereby slowing down user adoption.

One such area is the AR/VR or augmented- and virtual reality applications. These technologies, typically AR, superimpose an image over a view of the user’s actual environment. A handheld device can accomplish this, such as a smartphone. Others can be user-worn glasses, headsets, or a projection such as heads-up displays in vehicles.

AR technology commonly includes offering information about the environment around the user, for gaming or for safety reasons. On the other hand, VR technology immerses the user in a virtual environment. That means, VR implementation typically requires the use of a headset, completely covering the user’s eyes, thereby blocking out the world around them.

However, the adoption of AR and VR has so far been limited, and these have remained relatively niche markets. The primary reason for this is their footprint. For instance, AR use requires wearing bulky glasses, lenses, or headwear, or, holding the smartphone up to view the AR environment. Wearing such heavy, unbecoming devices for any duration can be very uncomfortable.

For engineers, the size of connectors has been one of the biggest challenges when they try to limit the size of devices for embedded and wearable systems. Although semiconductor sizes have progressively reduced, communication devices have stayed the same. Therefore, even with custom cabling, the cable size and its corresponding connector are the factors limiting the system size.

For the success of AR and VR solutions, it is necessary for their form factor to be small, comfortable, and lightweight for the user. These technologies also demand significant processing power as well as high-quality displays. Meeting this demand requires design engineers to use connectors that offer not only robust communication capabilities, but also minimize the weight and footprint.

Molex is now offering a quad-row connector that meets the above needs. The package is significantly smaller than those available in the market while offering many connectivity options.

The quad-row connector from Molex offers its performance gains because of its staggered-circuit layout that offers a 30% space-saving over the design of its competitors. The quad-row connector achieves this as it positions its pins across four rows with a pitch of 0.175 mm. Such a staggered-circuit layout is a substantial space-saver in many applications involving wearable, smartphones, smartwatches, and AR and VR devices.

According to Molex, users can also have a soldering pitch of 0.35 mm in the quad-row connectors. This matches with the standard surface-mount technology processes. That means that as electronic devices gain popularity and size reduction, manufacturers can scale their products by shifting to the 0.175 mm soldering pitch. These connectors from Molex can also integrate into moving objects, and withstand drops, vibrations, and other harsh conditions of use. Molex builds its quad-row connectors with interior armor and insert-molded power nails, making them substantially reliable and robust. The connectors are available in 32- and 36-pin varieties, with 64-pin configurations for the future.

Magnetic Position Sensing in Robots

Robots often operate both autonomously and alongside humans. They greatly benefit the industrial and manufacturing sectors with their accuracy, efficiency, and convenience. By monitoring motor positions at all times, it is possible to maintain not only system control but also prevent unintentional motion, as this can cause system damage or bodily harm.

Such monitoring of motor positioning is possible to implement by contactless angle encoding. It requires a magnet mounted on the motor shaft and provides an input for a magnetic encoder. As dirt and grime do not influence the magnetic field, integrating such an arrangement onto the motor provides a compact solution. As the encoder tracking the rotating magnet provides sinusoidal and 90-degree out-of-phase components, their relationships offer quick calculations of the angular position.

As the magnet rotates on the motor shaft, many magnetic encoding technologies can offer the same end effect. For instance, Hall-effect and magnetoresistance sensors can detect the changing magnetic field. 3D linear Hall effect sensors can help with calculating angular positions, while at the same time, also offering compensations for temperature drift, device sensitivity, offset, and unbalanced input magnitudes.

Apart from signal-chain errors, the rotation of the magnet also depends on mechanical tolerances. This also determines the quality of detection of the magnetic field. A final calibration process is necessary to achieve optimal performance, which means either harmonic approximation or multipoint linearization. With calibration against mechanical error sources, it is possible for magnetic encoding to achieve high accuracy.

The driving motor may connect directly to the load, through a gearbox for increasing the applied torque, through a rack and pinion, or use a belt and screw drive for transferring energy elsewhere. As the motor shaft spins, it transfers the kinetic energy to change the mechanical position somewhere in the system. In each case, the angle of the motor shaft correlates directly to the position of the moving parts of the system. When the turns ratio is different from one, it is also necessary to track the motor rotations.

Sensorless motor controls and stepper motors do not offer feedback for the absolute position. Rather, they offer an estimate of the position on the basis of the relative change from the starting position. When there is a loss of power, it is necessary to determine the actual motor position through alternate means.

Although it is possible to obtain the highest positional accuracy through the use of optical encoders, these often require bulky enclosures for protecting the aperture and sensor from contaminants like dirt and dust. Also, it is necessary to couple the mechanical elements to the motor shaft. If the rotational speed exceeds the mechanical rating of the encoder, it can lead to irreparable damage.

No mechanical coupling is necessary in the case of magnetically sensed technologies like magnetoresistive and Hall-effect sensors, as they use a magnet mounted on the motor shaft. The permanent magnet has a magnetic field that permeates the surrounding area, allowing a wide range of freedom for placing the sensor.

RF MEMS Switches for 5G Networks

For high-power RF designs like 5G networks, Menlo Micro has added an RF MEMS switch that contains an integrated driver circuit for a charge pump. The RF MEMS switch operates from DC to 6 GHz.

The new RF switch from Menlo Micro is one of a family of SP4T or single-pole/four-throw, DC-t0-6 GHz switch, and is meant for 5G infrastructure, measurement, and testing equipment involving high-power RF switching applications. Menlo Micro is using its own Ideal Switch technology for the high integration MM5140 SP4T switch. The technology gives the new switch power handling capability up to 25 W, an ultra-low insertion loss, and the highest linearity in the industry. The MM5140 SP4T switch easily outperforms all types of traditional solid-state switches and electromechanical relays.

The MM5140 SP4T switch performs RF operations at high power levels over a wide temperature range of -40 °C to +85 °C, delivering superb linearity from DC to 6 GHz. 5G RF applications demand significant reductions in distortion, which the switch’s IP3 of 95 dBm provides conveniently.

Menlo Micro has custom designed a built-in high-voltage charge pump or driver circuit and integrated it into the LGA package of the MM5140 SP4T switch. The charge pump circuit has both GPIO and SPI digital interfaces so that any test system or host processor can keep control over it.

Although the new module has the existing MM5130 at heart, it also has the CMOS charge pump driver ASIC, driver circuitry, and other peripheral passive components in its 5.2 X 4.2 mm package.

As the MM5140 SP4T switch is a single-pole four-throw device, the voltage must route over to each of the four gate lines. This requires the presence of either a MOSFET drive circuit or a dedicated multiplexer IC. Along with the integrated charge pump and the driver circuitry, the MM5140 SP4T switch saves board area and bill of materials.

The integrated passive components include a large capacitor that the charge pump requires for handling the high voltage that drives the MEMS. This helps reduce the BOM for passive components.

The difference between the MM5130 and the MM5140 is their operational speed. The MM5130 is a design meant to operate at higher frequencies, such as the microwave band. The design of the MM5140 is meant for a sub-6 GHz application. The MM5140 comes in an LGA package rather than the WLCSP of MM5130. That makes it easier for customers to design their boards, as the LGA package has a bigger pitch.

Moreover, Menlo Micro has eliminated some external components for the MM5140 design reduces its complexity. This helps in simplifying RF front-end development including receivers and transmitters, beamforming antennas, and RF filters. These are necessary for radar systems and advanced radio architectures.

5G base stations typically use RF/microwave solid-state switches and RF electromagnetic relays that the MM5140 SP4T switch can replace. The replacement offers significant improvements over the competing technologies, especially in the integrated capability, BOM count reduction, and real-estate savings on the board. Moreover, the MM5140 SP4T switch exhibits far better reliability over the other competing technologies.

Wi-Fi 5.0 to Wi-Fi 7.0

Both on smartphones and in living rooms, the audio & video streaming revolution is producing an insatiable demand for speed and bandwidth. To satisfy this demand, in the early 2010s, we had the Wi-Fi 5. However, this lasted only for a decade or so, because by then, consumers had bidirectional video applications such as Webex, WhatsApp, and other social media uploads like TikTok. These had begun to alter not only the consumer landscape but also that of the enterprise.

That led to the catapulting of Wi-Fi 6 to the arena for better management of the huge traffic of streamlining wireless transmissions. This was followed by Wi-Fi 6E which literally extended the benefits of its predecessor with the availability of the 6 GHz band. The pandemic of Covid-19 in 2020 was the moment for Wi-Fi 6 and Wi-Fi 6E, as is evident from the 1+ billion chips of Wi-Fi 6 and Wi-Fi 6E that Broadcom shipped in the past three years.

And still, the demand for higher bandwidth and speed continues only to increase. A recent study has shown that consumer spending on games has increased by 40%. This involves not only devices operating at higher speed, but also the use of newer technology like AR or augmented reality and VR or virtual reaility headsets as new gaming devices. While these devices demand unprecedented levels of immersion while playing, they also call for deterministic and reliable wireless data.

So, we are now moving towards Wi-Fi 7. It has the ability to incorporate 320-MHz channels into the 6 GHz band and employ the 4096-QAM modulation technique, thereby effectively doubling the channel bandwidth. Additionally, it employs better technologies for lowering latency and bolstering determinism. These include AFC or automatic frequency coordination and MLO or multi-link operation.

Wi-Fi 7 comes with spectrum flexibility spanning three bands. However, the critical role is played by the incorporation of 320 MHz channels into the 6GHz band for doubling the speed. For boosting the coverage and the overall network performance, there is the 4096-QAM technique that plays a crucial role.

Wi-Fi 7 can rapidly aggregate channels in congested, high-density networks. This is due to its MLO or multi-link operation that significantly improves its deterministic performance. By rapidly switching traffic among several channels, Wi-Fi 7 can drive greater capacity, thereby facilitating commercial-grade QoS or quality of service in its networks.

Another technology that Wi-Fi 7 utilizes is AFC or automatic frequency coordination. This technique allocates optimum spectrum, thereby enabling high-power access points and extending the 6 GHz range outdoors and indoors. According to Broadcom, its Wi-Fi 7 designs with AFC are capable of 63 times greater transmitting power. This helps not only to extend the range but also the coverage of the 6 GHz band in use.

Therefore, with its immense focus on speed, latency, and determinism, Wi-Fi 7 has entered our lives and is here to stay. According to the forecast of industry technology analysts, revenue from Wi-Fi 7 will supersede that from any other Wi-Fi technology so far in the next five years.

What are Piezoelectric Audio Devices?

The piezoelectric effect is a versatile and extremely useful phenomenon. Engineers have adopted this phenomenon in various transducer applications. Some of these applications involve transforming the applied voltage to mechanical strain output, for use as a basic source of sound. In a complementary mode, the application of mechanical stress to the Piezo material causes the rugged sensor to produce a voltage. Piezoelectric devices are low-cost, reliable, and rugged, and this allows engineers to exploit their unique properties.

Piezo-based speakers offer many attributes as sound sources. Unlike electrodynamic speakers, piezo-based speakers can be relatively thin, yet create very high sound pressure levels. However, mechanical and physical material issues can limit their audio quality. Now, a team at MIT is changing all this. They have developed a dense array of tiny dome speakers that they have based on Piezo technology. They have significantly transformed the classic analog function of loudspeakers. Their new loudspeakers are paper-thin, very flexible, and fully capable of turning any surface into an active audio source.

Although there are conventional thin-film loudspeakers, the basic requirement is the film must be free to bend to produce sounds. Firmly mounting such thin-film loudspeakers to a surface would attenuate their output and dampen the vibrations, while limiting their frequency response tremendously.

However, the ingenious approach of the MIT team has solved the problem in a rather unique way. Their new loudspeaker does not have to vibrate the entire material surface. Rather, they have fabricated tiny domes on a thin layer of piezoelectric material, such that each dome can vibrate independently. Each dome is about 15 µm in height, and they move up and down by only half a micron when vibrating. As each dome forms a single sound-generating unit, it requires thousands of these tiny domes to vibrate together to produce audible sounds. While the basic loudspeaker is only 120-µm thick, it weighs only 2 grams. Only standard processes are necessary to manufacture this loudspeaker at low costs.

Spacer layers surround the domes on the bottom and top of the film. This helps to protect the domes from the mounting surface, and at the same time allows them to freely vibrate. These spacer layers also protect the domes from impact and abrasion during daily handling, thereby enhancing the durability of the loudspeaker.

To make the film loudspeakers, the researchers used a thin sheet of PET or polyethylene terephthalate. This is a standard plastic used for a variety of applications. They used a laser to cut tiny holes in the sheet while laminating its underside with an 8-µm thick film of PVDF or polyvinylidene fluoride. This is a common industrial and commercial coating. Then they applied vacuum and heat to bond the two sheets.

As the PVDF layer is very thin, the pressure difference that the vacuum creates together with the heat causes it to bulge, but it cannot force its way through the PET layer. This makes the tiny domes protrude through the holes. The researchers laminated the free side of the PVDF layer with another layer of PET and this acts like a spacer between the bonding surface and the domes. Regardless of the rigid bonding surface, the film loudspeaker could generate a sound pressure level of 66 dB at 30 cm.

What are Reed Switches?

A modern factory will have several electronic devices working, and most of them will have several sensors. Typically, these sensors connect to the devices using wires. The wires provide the sensor with a supply voltage, a ground connection, and the signal output. The application of power allows the sensor to function properly, whether the sensor is sensing the presence of a ferromagnetic metal nearby, or it is sending out a beam of light as a part of the security system. On the other hand, simple mechanical switches, like reed switches, require only two wires to trigger the sensors. These switches need magnetic fields to activate.

The reed switch was born and patented at the Bell Telephone Laboratories. The basic reed switch looks like a small glass capsule that has two protruding wires. Inside the capsule, the wires connect to two ferromagnetic blades with only a few microns separating them. If a magnet happens to approach the switch, the two blades attract each other, making a connection for electricity to flow through them. This is the NO type of reed switch, and it is a normally open circuit until a magnet approaches it. There is another type of reed switch, the NC type, and it has one blade as a non-ferromagnetic type. This switch is a normally closed type, allowing electric current to flow until a magnet approaches it. The approaching magnet makes the blades pull apart, breaking the contact.

Manufacturers use a variety of metals to construct the contacts. This includes rhodium and tungsten. Some switches also use mercury, but the switch must remain in a proper orientation for switching. The glass envelope typically has an inert atmosphere inside—commonly nitrogen—to seal the contacts at one atmospheric pressure. Sealing with an inert atmosphere ensures the contacts remain isolated,  prevents corrosion, and quenches sparks that might result from current interruption due to contact movement.

Although there are solid state Hall effect sensors for detecting magnetic fields, the reed switch has its own advantages that are necessary for some applications. One of them is the superior electrical isolation that reed switches offer compared to what Hall effect sensors do. Moreover, the electrical resistance introduced is much lower for reed switches. Furthermore, reed switches are comfortable working with a range of voltages, variable loads, and frequencies, as they function simply as a switch to connect or disconnect two wires. On the other hand, Hall switches require supporting circuitry to function, which reed switches do not.

For a mechanical switch, reed switches have incredibly high reliability—they typically function for billions of cycles before failing. Moreover, because of their sealed construction, reed switches can function even in explosive environments, where a single spark could generate disastrous results. Although reed switches are older technology, they are far from obsolete. Reed switches are now available in surface mount technology for mounting on boards with automated pick-and-place machinery.

The functioning of reed switches does not require a permanent magnet to actuate them. Even electromagnets can turn them on. Initially, Bell labs used these switches abundantly in their telephone systems, until they changed over to digital electronics.

What are Solid-State Batteries?

The transport industry is currently undergoing a revolution with EVs or electric vehicles on the roads. EVs require batteries, and many EV manufacturers are now manufacturing their own batteries, targeting low-cost batteries with the most range and the fastest charging speed. While many industries are still using lithium-ion batteries, others are moving towards solid-state batteries. Compared to a few years ago, major breakthroughs are finally bringing solid-state batteries closer to mass production.

Although solid-state batteries have been in existence for some time now, and scientists have been researching them, they have been commercially available only in the last decade or so. Specific advantages of solid-state batteries include lower costs, superior energy density, and faster charging times.

Many companies have been researching solid-state battery technology for years. For instance, Toyota claims to be on the verge of producing solid-state batteries commercially for EVs, and they hold more than 1,000 patents.

Conventionally, a lithium-ion battery has an anode and a cathode, with a polymer separator keeping them apart. A liquid electrolyte floods the entire cell and is the medium through which lithium ions can travel while the battery is charging/discharging.

In a solid lithium-ion battery, a solid electrolyte layer separates the anode and the cathode, allowing lithium ions to travel through it. The anode is of pure lithium, which gives it a higher energy density than that of regular batteries. Theoretically, the energy density from solid lithium-ion batteries is roughly about 6300 watts per hour. Compared to the energy density of gasoline, a solid lithium-ion battery offers an energy density of about 9500 watts per liter.

The major advantage of solid-state batteries is their smaller size and weight. Additionally, they pose no fire hazards. As these batteries are very safe, they do not require as many safeguards to secure them. Their smaller size allows packing them to higher power capacity, and they do not release toxins. Solid-state batteries run 80 percent cooler than regular batteries.

With all the above advantages, using solid-state batteries in electric vehicles offer them greater range, safer operation, faster charging, higher voltages, and longer cycle life. However, solid-state batteries must overcome some disadvantages still.

The first of these obstacles is the dendrite formation. Lithium is a highly corrosive metal, requiring the use of chemically inert solid electrolytes. Over time, dendrite growth increases to the extent of destroying the battery. During charging, these batteries usually grow spike-like structures that can develop and begin to puncture the dividers, causing short-circuits in the battery. Manufacturers are using ceramic separators to overcome the dendrite menace.

Solid-state batteries currently do not perform well at low temperatures. This affects its long-term durability.

So far, the biggest detriment to solid-state batteries has been their exorbitant cost. However, present indications from manufacturers like Toyota suggest they have surmounted the price barrier.

Therefore, at present, the only problem still remaining for solid-state battery commercialization is their low-temperature performance. To be a viable alternative, solid-state batteries must perform in all kinds of variable environments and climates. However, manufacturers are offering assurances that they have overcome this hurdle also. Recharging stations need to be able to handle the faster-charging currents as compared to that of regular lithium-ion batteries.

What are Stacked 3D ICs?

Just like any big city, electronics is evolving with great rapidity, such that both are running out of open space. The net result is a growth in the vertical direction. For a city, vertical growth promises more apartments, office space, and people per square mile. For electronics, there is the slowing of Moore’s law and the adoption of new advanced technology. That means chip developers cannot increase density and speed from shrinking processes and smaller transistors. Although they can increase the die capacity, this suffers from longer signal delays that reduce yield. That limits the expansion in X-Y directions, which means the only option remaining is building upwards.

Among the many established forms of vertical integration, there are 2.5D ICs, flip-chip technology, inter-die connectivity with wire bonding, and stacked packages. However, all these suffer from constraints that limit their value. Three-dimensional integrated circuits or 3-D ICs offer the highest density and speed.

Three-dimensional ICs are monolithic 3-D SoCs built on multiple active silicon layers. These layers use vertical interconnections between the different layers. So far, this is an emerging technology and has not been widely deployed. Furthermore, there are stacked 3-D ICs with multiple dies that manufacturers have stacked, aligned, and bonded into a single package. They use TSVs or through silicon vias, and a hybrid bonding technique to complete the inter-die communication. Stacked 3-D ICs are now commercially available, offering an option for larger dies or migration to leading-edge nodes that are very expensive.

Stacked 3-D ICs offer an ideal option for applications requiring more transistors in a given footprint. For instance, a mobile SoC requires high transistor densities but has limits on its footprint and height. Another example is cache memory chips. Manufacturers usually stack them on top of or below the processor to increase their bandwidth. This makes stacked 3-D ICs a natural choice for applications that are on the limits of a single die.

Vertical stacking offers a smaller footprint with faster interconnections compared to multiple packaged chips. Rather than a single large die, splitting it into several smaller dies provides a better yield. For the manufacturer, there is flexibility in stacking heterogeneous dies, as they can intermix various manufacturing processes and nodes. Moreover, it is possible to reuse existing chips without redesigning them or incorporating them into a single die. This offers a substantial reduction in risk and cost.

Although there are numerous benefits and opportunities from the use of stacked 3-D ICs, they also introduce new challenges. The architecture of 3-D silicone systems needs a more holistic approach, taking into account the third dimension. It is not sufficient to think of 3-D ICs only in terms of 2-D chips stacked on top of each other. Although it is necessary to optimize power, performance, and area in the familiar three-way approach,  the optimization must be in every cubic millimeter rather than in every square millimeter. All tradeoff decisions must take into account the vertical dimension also. This requires making the tradeoffs across all design stages, including IP, architecture, chip packaging, implementation, and system analysis.

Remote Sensing with nRF24L01+ Modules

RF modules, nRF24L01+, from Nordic Semiconductor, are low-cost solutions for two-way wireless communication. Users can configure the modules via their SPI or Serial Peripheral Interface. The SPI interface also allows control over a microcontroller. The Internet has many examples of projects using these RF modules with Arduino boards.

The RF module nRF24L01 has a built-in PCB antenna. Moreover, the module has an extra feature that utilizes the two-way communication feature for detecting any loss of communication between the transmitter and the receiver. The modules offer two-way communication because they act as a transmitter and a receiver at the same time. However, one module acts as the main transmitter and transmits the state of a PIR or Passive Infrared Sensor to the other module that receives the data for further processing.

Remote sensors need this ability to detect the loss of communications. This is because, in the absence of communication, it is easy to lose data or information without notice. Again, this is an important feature when installing the sensor to verify if both RF modules are actually talking to each other, and are not out of range.

Although the RF modules nRF24L01 need powering with 3.3 VDC, their IO pins are 5 VDC tolerant. That makes it easy to connect the SPI bus of the nRF24L01 modules to an Arduino Pro Mini working on 5 VDC.

It is very significant to place the power supply bypass capacitors as close as possible to the microcontroller and the nRF24L01 modules, as this effectively suppresses most of the switching noise from these chips. Overlooking this in such projects often leads to all types of unexpected problems. It is also necessary to use multiple bypass capacitors. Users can effectively parallel capacitors of different values, like an electrolytic capacitor of 100 µF and a polypropylene capacitor of 100 nF. The electrolytic capacitor filters out noises of lower frequencies, but it is ineffective for filtering any high-frequency noise. The polypropylene capacitor filters the higher frequency noise.

The PIR sensor connects to the microcontroller. A voltage level translator offers the sensor the optimum voltage level it needs to function. Therefore, depending on the type of PIR sensor, the voltage level translator can supply a 5 VDC, 3.3 VDC, or other lower level outputs. The polarity of the voltage level translator transistor decides whether the trigger output is high active or low active.

A red LED begins to flash when the transmitter and the receiver have lost their connection. On restoring the connection, the red LED stops flashing.

When the PIR sensor senses motion, a blue LED lights up to indicate this. The transmitter sends this trigger event over to the receiver as a trigger code byte. If there is no motion to detect, the transmitter sends only a live beat code to the receiver. This is how the receiver knows if the sensor has sent a motion trigger.

The receiver sends the same code it receives back to the transmitter as an acknowledgment. There is thus continuous communication between the receiver and the transmitter, and both can easily determine as soon as they have lost connection.

What is a PolyFuse?

Electronic circuits often have fuses on board the PCB. Fuses protect the circuitry from catching fire due to overload. Because of some fault like a short-circuit, a part of the circuit may start drawing more power than it is admissible. The additional power flow may lead to overheating and finally, a fire can break out. A fuse acts as a circuit breaker to protect against overload by interrupting the power flow. Typically, the fuse element is a thin wire with a low melting point. Higher power through the fuse means more increased current flow through it, which heats the wire and causes it to melt or blow. This interrupts the power flow.

Although the fuse wire acts as a protection, one of its drawbacks is it needs a physical replacement once it is blown. This is a problem for electronics at a remote location because the device will remain inoperative until someone fixes the problem and replaces the damaged fuse with a new one. This drawback has led to the development of PolyFuse.

There are electromechanical devices that act as self-resetting circuit breakers. However, most of such devices have a rating of 1A and above. Moreover, their physical size is not suitable for printed circuit boards. A PolyFuse is a self-resetting circuit breaker suitable for low voltage, low current electronics. Moreover, its physical size is small enough to allow its use on a small printed circuit board.

PolyFuses are similar to PTC or positive temperature coefficient resistors—initially, their resistance is low enough to allow the load current to flow unhindered. However, in case of an overload, the PolyFuse starts to heat up, and its resistance also increases. This helps in cutting down the load current through it. However, unlike PTCs, PolyFuses have a self-healing property. If the current through a PolyFuse reduces, its resistance drops back to a lower value. This is their self-resetting property.

A PolyFuse typically contains an organic polymer substance with the impregnation of carbon particles. The carbon particles are usually in close contact, as the polymer is in a crystalline state. This allows the resistance of the device to be low initially.

As current flow increases, the carbon in the PolyFuse heats up, and the polymer begins to expand in an amorphous state. This causes the carbon particles to separate, increasing the resistance of the device and a subsequent increase in the voltage drop across the PolyFuse, which leads to a decrease in the current flow through it. The residual current flow under the fault condition keeps the PolyFuse warm enough to limit the current. As soon as the cause of the overload is removed, the current reduces to allow the PolyFuse to cool down, regain its low resistance, and the correct operation to resume.

PolyFuses cannot act fast, because they need to heat up before limiting the current flow. That means they have a short but appreciable time delay before they operate. Hence, they are not very effective against fast surges and spikes. However, they are very useful because of their self-resetting property, making them effective against short-term short-circuits and overloads.