What advances in circuit protection are having the biggest impact on the industry?
Matt Burns, Global IP&E Technical Marketing Specialist, Avnet Electronics Marketing Americas, www.avnetexpress.avnet.com
I see three basic trends in in this area. One is miniaturization. Mobile products in the consumer, medical, industrial and mil/aero markets have increased functionality in smaller form factors. This forces the circuit protection manufacturers to develop consistently smaller single-channel devices and tightly packed multi-channel arrays. ESD protection devices have been shrinking in size for some time, but other circuit protection devices like fuses and hybrid protectors have reduced footprints as well.
Second, consumer products continually support higher data throughput whether streaming high definition video on tablets and LCD TVs or migrating to second and third-generation protocols on computers and computer peripherals. The electrical protocols used to support these applications (HDMI, DisplayPort, USB 3.0, PCIe 3.0, etc.) have data rates in the Gbps ranges. Providing ESD protection at higher frequencies and higher data rates requires consistently smaller device capacitance and faster response times. The circuit protection manufacturers consistently innovate to the needs of the market. The current generation of ESD protection devices provide sub-picofarad channel capacitance and nanosecond response time.
Lastly miniaturization, continual progress in material science and the need for increased product ruggedness and reliability provide opportunities for circuit protection manufacturers to broaden their hybrid protection portfolio. Many new combinations in a single device are now available: Zener diodes and PPTCs, MOVs and GDTs, MOVs and PPTCs, bimetals and PPTCs. This list goes on. Each hybrid protection scheme answers a specific circuit protection need. This trend started as a trickle, but I further expect to see more offerings going forward.
|Tom Colella, Engineering Manager, Electrocube, Inc., www.electrocube.com
The generation of inductive or switching transients is a well-known phenomenon to design engineers and field technicians. The suppression of these transients is required for two general purposes: for contact protection and/or prevention of electromagnetic interference (EMI) generation. When arc suppression is required, the suppression device is placed across the switching device. When EMI is to be suppressed, optimum results are obtained when the suppression device is placed across the load, particularly if long leads are required between the switching device and the load.
Many techniques have been devised to eliminate or suppress the transients, but which method is most effective? Taking features such as size, cost and effect on the circuit into consideration, the most effective application is a series Resistor-Capacitor (RC) Network. But, what RC value combination is needed and how is it determined? Before purchasing a RC Network, determine RC in one of two ways. Calculate R using this formula: C = (I2/10)Mfd. Calculate C using this formula: R = E/10(3.16vC)(1+50/E). For reference, C = Capacitance in Mfd. | I = Load Current in Amps | R = Resistance in Ohms | E = Source Voltage.
However, calculating RC value can be difficult to determine by formula due to contributing factors such as equipment wiring and component location – which can vary from machine to machine.
A Resistor-Capacitor Substitution Box (RCSB) is a time-saving second option that eliminates the need for a toolbox full of individual resistor and capacitor values. Temporarily clip the RCSB into the circuit. Then, with the aid of a storage oscilloscope, select and match various combinations of resistors and capacitors to optimize spike reduction and/or and reduce EMI levels.
Bharat Shenoy, Littlefuse, www.littelfuse.com
The advancement of the ultra low resistance Polymer Positive Temperature Coefficient (PTC) resettable fuse will impact the industry moving forward. Innovations in material science over the last few years have allowed PTC component makers to reduce the resistance of PTC’s, for instance in Li-ion battery applications. Low resistance is critical in battery applications for smartphones and tablets due to the need to maximize battery life. Polymer Positive Temperature Coefficient resettable fuses are made of a polymer material which is loaded with conductive particles. When the PTC resettable fuse is under normal operating conditions, the resistance is low and allows current to flow. When fault current increase due to short circuit or overload, the device temperature increases due to i^2R heating.
The polymer expands and the conductive chains inside the material pull apart increasing the resistance. If enough current flow, the devices switches to a very high resistance and essentially acts like a fuse cutting of the fault current. When fault is removed, the device cools back down and returns to low resistance state. The material is actually a conductive plastic so the resistance of PTC resettable fuses has always been on the high side compared with one-time blow fuses or semiconductor switching devices like MOSFETs. So, the challenge is to bring the resistance down for PTC resettable fuses. Low resistance means less voltage drop and less resistive losses for customer applications. The way to do this is improve the performance of the conductive fillers that are loaded into the polymer material. PTCs are great protection devices for Li-ion batteries since they can sense both the heat and current building up in a battery pack during a fault condition. It essentially acts as both an overcurrent and over-temperature protector. This is critical for Li-ion battery applications.
|Michael Greenspan, ECN Reader
IMHO, with advances in MOSFETS, they have become tiny, low-cost, fast, with high voltage capabilities, and with milliohm on-resistance, so one has much less need for things like fuses or NTC resistors to protect against over-voltages or surge currents. One can simply detect the offending conditions with very simple input circuitry and use the MOSFET to disconnect the high voltage, or regulate the surge current. It also becomes much easier to design circuits that accept very wide conditions of operation without really needing to "protect" them. For example, a simple DC source that once needed to be protected against overvoltage will now work fine with either 115 VAC or 230 VAC and can handle a spike of 600 volts with no problems.
Cliff Ortmeyer, Technical Marketing Manager, Newark element14, www.Newark.com
In numerous applications, relays are used to shut off loads. The loads often have some type of galvanic isolation requirement (electrically isolated from the main circuit) for safety purposes. Relays are and continue to be a cost-effective and reliable method of load control. That being said, if power conservation, as well as board space and size are key considerations, other types of switches, such as triacs for AC load control, can also be used. The main drawbacks with triacs replacing relays has traditionally been both the cost and reliability of the additional circuitry involved to protect the triac from electrical surges, as well as adding isolation.
One of those drawbacks has been removed with the adoption of triacs with integrated protection mechanisms. These types of triacs have been around for a while but have had limited adoption due to a variety of reasons including lack of understanding of the devices’ operation, the additional cost of isolation, as well as the general acceptance curve of any new technology, especially when safety is involved. These self-protected triacs, or AC Switches, were introduced by STMicroelectronics years ago and more recently by NXP.
One of the main reasons for concern with a triac is its failure mechanism when exposed to an overvoltage pulse. When a triac fails, it is most likely going to fail in a shorted mode, which can lead to the load being powered with no method of control. The unique feature with these types of AC switches is that upon encountering an overvoltage, they turn on the triac in a controlled manner, thus reducing the overvoltage and disseminating the energy in the surge. This helps to protect the triac from failing and disseminates the energy pulse.
This type of protected triac is currently used in multiple applications and, with more time and awareness, will continue to be adopted in more safety-critical applications.
|Rudye McGlothlin, Marketing Manager, Digital Isolation Products, Silicon Labs, www.silabs.com
In most embedded systems, circuit protection adds no discernible value to the end user. While the system designer may lose sleep worrying about how to protect a microcontroller and other embedded components from harsh operating environments, the consumer rarely gives circuit protection a thought. Consumers do not pour over solar inverter brochures looking for which system has circuit protection designed to resist the largest, fastest glitches produced by modern switches used in power converters. They do not consider whether the circuit protection device will be the point of first failure in the system. Yet it is precisely these circuit protection considerations that allow the system designer to take full advantage of modern switches and power architectures.
The features that consumers do care about in electronic products, such as energy efficiency, reliability and product lifespan, are directly influenced by the circuit protection the designer chooses. Select a circuit protection solution with a slow response time, and the switch turn-on signals must be moved farther apart, resulting in a loss of efficiency. Use an outdated optocoupler-based protection solution in the design, and the lifespan of the end product is immediately reduced. Choose a device with poor common mode transient (CMT) rejection, and the designer must worry about high-voltage transients disrupting the switching cycle. The wrong circuit protection choice can reduce performance and potentially lead to system damage.
Modern CMOS-based digital isolation technology alleviates many of these concerns. System lifetime and robustness when operating in noisy, harsh environments are both addressed and improved when using digital isolators. With their high CMT immunity, digital isolators reject fast switching glitches that otherwise affect system performance. The inherently tight timing specifications of digital isolators also allow the designer to create highly efficient solar inverters and other electronic systems with no performance compromises.
Ultimately, robust digital isolation components provide a high level of circuit protection that enables system designers to provide the product features that consumers expect. That’s valuable.
Robert Hilty, CTO, TE Circuit Protection, www.TE.com/CircuitProtection
One of the biggest changes taking place in the consumer electronics industry is the rapid rise of tablet computers. These sleeker, slimmer and converged devices are replacing traditional notebook PCs in popularity. They are also integrating functionality from single function devices, such as digital cameras and video cameras. These devices are spurring the evolution of battery cell technology, since thin, envelope-like lithium polymer, or LiP, cells offer new space-saving options in these designs compared to disc-shaped or cylindrical cells.
Recent changes in device form factors and battery technology have created a new landscape for circuit protection technology. Space constraints have always been a concern for component suppliers who serve the consumer devices market, but now it’s not just board surface area driving design, it’s also the profile of the end device. You have to continue to innovate in order to meet the space constraints of slimmer more compact designs and, at the same time, comply with stringent safety and efficiency standards. For lithium cell protection, for instance, new hybrid circuit protection devices combine existing technologies and materials sciences by connecting a bimetal protector in parallel with a PPTC device. These circuit protection devices offer the low thermal cut-off temperatures, high hold-current ratings and thin, compact sizes needed to accommodate LiP cell design requirements.
Data rates continue to increase. For example, the latest USB 3.0 protocol provides data transfer rates almost ten times higher than the previous-generation USB 2.0 version (5Gb/s vs. 480 Mb/s). However, these faster data-rates have also intensified the need for new and more robust protection against electrostatic discharge (ESD). In response you see extremely low-capacitance ESD protection devices with low insertion loss. Tests have shown that the most advanced silicon ESD devices, for example, provide extremely low impact on logic levels and negligible signal-distortion impact, which is a major consideration in sensitive electronics.
Finally, smart phones contain all the functionality (e.g., camera, video, GPS) that was once offered in separate portable consumer products. This means that components manufactures now find themselves in a landscape where competitors must fiercely vie for the same space. As a result, meeting the existing – and future – market trends by applying circuit protection technologies that help enable leading-edge designs is essential to their success.
Dennis Newman, ECN reader
Heat generated by ckts. is energy wasted. Transforming heat back into renewable/reusable energy, with or for the ckt, before it becomes detrimental upon the circuit is (as long as I’ve experienced with electrical and electronics) and has always been a most desirable design need.
Technology is approaching such ability; if not already in use by institutional bodies not associated with commercial or consumer levels of accessible knowledge.