Two winding PFC input circuit. The impedance characteristic, although nonlinear, is continuous and displays no time delay such as that associated with the spark-over of a gap or the triggering of a thyristor. In fact the ESD9L5.0 includes a low breakdown Zener diode and a pair of high breakdown, and therefore low capacitance, standard diodes as shown in Figure 5. During manufacture, the zinc oxide granules are pressed before being fired for a controlled period and temperature until the desired electrical characteristics are achieved. selenium rectifiers, avalanche (Zener) diodes and varistors made of different materials, i.e., silicon carbide, zinc oxide, etc. IGBTs. As can be seen from the illustration below, the resistance value of the varistor or TVS diode rapidly drops to below 2 ohms when over-voltage is applied. New regulations concerning surge protection are forcing engineers to look for solutions that allow such protection to be incorporated at minimal cost penalty, particularly in cost-sensitive consumer products. Case 2—Calculating ac Dissipation: When a sinusoidal alternating voltage is applied to a varistor, the dissipation is calculated by integrating the VI product. 3. Other new varistor types incorporate a thermo fuse to provide a predictable “fail-safe” behavior in case of abnormal use. Three winding PFC input circuit. For example, in dc applications a large capacitance is desirable and can provide a degree of filtering and transient suppression. Fig. In a CAN with serial bus topology, the CANH and CANL signals are used to specify the dominant and recessive level state. The V-I characteristic curve of Varistor is similar to that of a Zener diode. Copyright(c) 2020 TDK Corporation. They are constructed of a sintered matrix of zinc oxide (ZnO) grains. of a varistor. However, the avalanche voltage is maintained across a thin junction area, leading to substantial heat generation. continuous operating voltage. The graph below shows the thermal characteristics of leak current in a representative chip varistor and TVS diode. The applicable Automotive Electronics Council standards also differ substantially, For most applications, you can determine the selection by assessing four aspects of the desired application: 1. It consists of an N-type semiconductor and a P-type semiconductor that are placed together. A resistor is an electric component that is used to provide resistance to current in the circuit. For an AC load, a varistor … Moreover, since varistors have a negative temperature coefficient, at a higher dissipation (and accordingly at a higher temperature) the resistance value will decrease and the dissipated power will increase further. The amount of energy expected to be dissipated will also influence this, and designers must ensure the package dimensions are appropriate to the physical and mechanical design of the product. The aim of this article is to clarify the difference between varistors and diodes and to introduce data that can be used to compare the two. Ldc > Lac improves the ac rejection ratio at the operating frequency of Iac (current in ac winding). So back to the bench, declaring that if two inductors share the same core the inductance is either mutual or leakage. Digital Transistors (BRTs) Darlington Transistors. 5. Varistors offer cost savings and performance advantages over crowbar-type surge protectors and Zener diode clamp devices in a wide range of applications. Inductive load switching: 1. relay coils 2. motors 3. solenoid coils 4. transformers 2. Like varistors, TVS diodes are transient voltage suppression devices useful for protecting electronic components. The latter is always chosen from a value of 10% or 20% of the maximum current. 2 shows a flowchart that may be used to determine the necessary steady-state voltage rating or working voltage. A diode is a type of electrical device that only allows current to move through it in one direction. I measured the total inductance of each inductor and their mutual inductance, and Figure 5 (see all figures below): Lm = Mutual inductance between LAC and LDC windings, LdL = Leakage inductance in the LDC winding, LaL = Leakage inductance in the ac winding. Based on operation, Transient Voltage Suppressors can be divided into two classes, clamping, and crowbar. They generally can therefore be used interchangeably in a circuit, but there are cases where chip varistors are considered to be not suitable. My challenge was that I could not divert the switching current from the input filter and circulate it in another loop. This current may not be cleared in an ac circuit—and clearing is even more uncertain in dc applications. the ambient temperature in the actual usage environment must also be taken into consideration. The ESD9L5.0 behaves as if it were a simple Zener diode. In conventional leaded devices, the inductance of the lead can slow the fast action of the varistor to the extent that protection is negated. They are silicon-based ESD protection components. For further reference, Fig. with breakdown voltage and capacitance being controlled by the number of layers and the interlayer design. Recently, I was designing a PFC unit for 800 Hz operation and had difficulty designing the input filter that eliminates EMI, but does not distort the power factor caused by the large currents in the X capacitors. A varistor’s behavior is defined by the relation: K is dependent on the device geometry. From the table, it can be seen that the CAN transceiver may be destroyed if a voltage of 4 kV or higher is applied. Devices such as gas discharge tubes, carbon blocks and semiconductor devices with non-linear voltage/current characteristics are not considered as VDRs in … To see this article in PDF format, please click here. IC logic switching:​ 1. TDK logo is a trademark or registered trademark of TDK Corporation. This design has been simulated in SPICE and bench tested on a T.I. When these conduct, they form a low ohmic path to absorb surge energy. The RCI will divert >30db of switching current from the input filter. What is a zener diode? Both two- and three-winding devices operate in the same manner as explained below: Ldc and Lac, which when loosely coupled (0.5< K<0.90) each form a leakage inductance. Input current of the original unit. (Click for enlarged view). A varistor, by contrast, displays a nonlinear, variable impedance. Areas of the array will force diodes in series, where their threshold voltages will sum. TVS diodes on the other hand are a combination of P-type and N-type semiconductors. All rights reserved. A voltage increase of only 2.26% will, in this case, double the dissipated power. 4. QPL Status for Wirewound 0603 Chip Inductors, Expanded Performance Range of Inductive Components. Since electrical conduction occurs, in effect, between Z N O grains distributed throughout the bulk of the device, the Littelfuse Varistor is inherently more rugged than its single P-N junction counterparts, such as Zener diodes. Those that divert the transient fall into two broad categories: crowbar devices that switch into a very low impedance mode to short circuit the transient until the current is brought to a low level; and clamping devices that limit the voltage to a defined level. As the illustration below shows, chip varistors have a laminated structure, Diodes on the other hand were used mainly for rectification, so their application area was different. Electrical and mechanical considerations must be taken into account when selecting the package size and style. The Zener diode comparison highlights the extended protect region the varistor also offers … A varistor, by contrast, displays a nonlinear, variable impedance. The resistance value of both chip varistors and TVS diodes changes greatly depending on the applied voltage. It has typical values of 500µH to control ripple current in the winding and switching device. In many cases, one needs to determine the ESD durability as a set, and the same performance is required of the electrostatic protection components. The company also mass-produces the industry's smallest AEC-Q200 compliant EIA 0402 (1.0 x 0.5 mm) size for automotive applications. Without varistor protection, the measured peak current through the pump motor when S is closed is 1A. What’s the difference between them? If you're looking for a surge protection device that delivers high levels of performance while addressing pressures to reduce product size and component count, then voltage dependent resistor or varistor technologies might be the ideal solution. Effective Surge And Lightning Strike Protection For AC And DC Power Line Applications. One advantage of the crowbar-type device is that its very low impedance allows a high current to pass without dissipating a considerable amount of energy within the protector. In this scheme, a Zener diode is connected anti-parallel with the laser diode. 1. 1 highlighting the distinct operating zones of the varistor. Not a pretty package, but a good start in understanding this topology. The designer did not have a good understanding of skin effect nor proximity losses. In a simple application of a parallel AC line protection element, why would I choose a varistor over a bidirectional TVS diode? Input current of the RCI unit. So I went back and searched the many papers on the subject, finding lots of higher math and transformer equivalent circuits. The leak current increases towards higher temperatures, but it is designed to not exceed 50 µA. There are several problems with this technique. Enhanced materials and optimized component design—particularly in the field of Zinc Oxide varistors—have opened up new applications for varistors, especially those requiring low protective level and a low standby current. 5. Resonant-coupled inductor circuits. The varistor varies the current up or down,the zener diode restricts the voltage to the value of the diode break down. Determine the repetitive peak current. Before … Maybe I can educate the engineering community and reap some small benefits. (Click for enlarged view). 6. There are many types of TVS device that can be used for Transient Voltage Suppression namely Metal Oxide Varistor, TVS Diode, Zener Diode or a Bypass Capacitor. Manufacturing costs are similar to a PFC inductor. The gap should be placed away from the windings or the fringing flux will increase winding resistance. A low coupling factor (K) is obtained by placement of the two windings on opposite sides of the core and gap. This unit with its smaller dual windings or triple windings can be packaged in a lower profile package, allowing better thermal flow. Full complete winding rows offer the best results. The word PFC (Power Factor Correction) is used throughout this document to denote one configuration that is widely known to the profession, but the RCI can be used in many different configurations as shown in Fig. The resultant magnetic package is about the same volume as a standard PFC inductor but in a lower profile that aids system packaging, thermal flow and noise shielding. The disadvantage is a reduction in the level of protection offered by an over-specified varistor. As Lm is reduced, the IAC component increases, affecting the external circuit. The ac winding carries high ac current so its resistance at the switching frequency (Rac) must be constructed as low as possible, so Litz wire is sometimes used. Zener diodes are used to make the voltage more stable. TDK also offers products that can substitute Zener diodes in applications involving frequent on/off switching such as for solenoid valves and stepping motors. Connecting the varistor across the load is effective when the supply voltage is 24 to 48 V, and across the contacts when the supply voltage is 100 to 240 V. The cutoff voltage Vc must satisfy the following conditions. Determine this capacitor value to resonate with Lac, leakage inductance. Therefore components with low insertion loss at 1 Mbps (= 0.5 MHz) must be selected. The varistor only has one graph, of clamp voltage against surge current. Choosing the right circuit protection is a crucial design decision. A surge protector may either attenuate a transient by filtering or divert the transient to prevent damage to the load. Surge protection devices protect against surges generated by electromagnetic effects, such as lightning or electrostatic discharge caused by a variety of effects. Digital Isolators. The slope of the protect region is determined by the device parameter β, which bears an inverse relation to a. When the varistor reaches the end of its operating life, the thermal disconnect will open the circuit, protecting against fires. This figure shows this varistor turning on when its voltage drop exceeds 100 V in either direction. This design has the current being shared (split into ac and dc) by the primary and secondary. Because the leak current of the electrostatic protection component is temperature dependent, Some diodes also use Au wire etc. Showing three full cycles of the switching waveforms. SPICE simulation using the calculated leakage inductance values as shown above and the coupling factor set to 1. Because chip varistors have a multilayer structure, capacitance can be increased by increasing the number of internal electrode layers. Electrostatic protection components inserted in parallel with the circuit should not obstruct communication at this speed. There is a coupled inductor where one winding has only AC current and the other with DC current. Current Protection. Arcing will occur across the opening contacts of the switch. The higher the nominal voltage of the selected varistor compared with the normal circuit operating voltage, the better its reliability is over time, as the device is able to withstand more surge currents without degrading performance. Note the slope of the ac current: if Ton × Ein/dI =Lm Then: 4µH × 400V/4.8A = 333µH (same value shown in 7). with AEC-Q101 being used for TVS diodes and AEC-Q200 for varistors. The Eval’s improvement was evident and all readings and waveform match the SPICE simulation. The figure to the right shows another ESD protection means commonly employed to protect laser diodes. Energy ratings for available varistors start at a few Joules up to several hundred Joules. Can be used in any topology, input or output, diverting switching current to ground. Selenium Cells - Selenium transient suppressors apply the technology of selenium rectifiers in conjunction with a special process allowing reverse breakdown current at high- Another growing market for surge protection is in the telecom sector, where continuously increasing intelligence in exchanges and throughout the networks leads to greater use of sensitive semiconductors, and the stringent demands on uptime and availability mean that high susceptibility to disturbances in supply is intolerable. Zinc oxide varistors developed in 1968 were adopted to protect diodes from lightning. A  K of ~0.6 is a good tradeoff. The normal operating conditions of the apparatus or system, and whether ac or dc voltage is applied. A Zener diode is a semiconductor device which conducts in forward biased as well as reversed biased. As such, surge protection may be applied at the mains input to combat disturbances on the mains supply external to the operating equipment or internally generated overvoltages usually caused by high inductive load switching. The RCI patent is currently pending (US 62/170,844) and the search results are very promising. Using an LCR meter, measure LAC, Ldc, and Lm. Diode and Transistor are considered as the backbone of electronic devices and Circuit. All rights reserved. The DC I−V characteristics of the ESD9L5.0 are the same as for a low voltage Zener diode. A normal diode if operated in reversed biased will get destroyed.Thus, a normal PN junction diode is considered as a unidirectional device. A high α implies a better clamp; zinc oxide technology has enabled varistors with a in the range 15 to 30—significantly higher than earlier generation devices such as silicon carbide varistors. 1 also compares the varistor characteristic with that of the ideal voltage clamping device, which would display a slope of zero, as well as a Zener diode characteristic. TVS diodes used to be almost exclusively uni-directional, but there are now an increasing number of bi-directional TVS diodes as well. The varistor granular structure does not allow for low clamping voltage. Zener—or avalanche diodes—and voltage-dependent resistors (varistors) display a variable impedance, depending on the current flowing through the device or the voltage across its terminals. Another limitation is power-follow, where a power current from the voltage source follows the surge discharge. The ac winding is sized according to the needs of the converter, which is known by those in the art. Chip varistors enable bi-directional electrostatic protection. Chip varistors and TVS diodes are commonly used as over-voltage protection components. In general, electronic circuits can be built with a various electrical and electronic components like resistors, capacitors, diodes, transistors, integrated circuits, transformers, Thyristors, etc. PETech. The clamping device itself is transparent to the supply and to the load at a steady state voltage below the clamping level. Note both SPICE simulations contain the same results proving the theory. Figures 8 to 14 are data taken from a TI UCC3817 (250W) demo board rev 5 with the original TI inductor (L1) and a two-winding RCI. Calorimeter Deliberately Drives Li-Ion Cells into Thermal Runaway and Explosion, PMIC Simplifies Power-Supply Design for Automotive Cameras, GaN Ups Efficiency in Next-Generation Wireless Chargers, Optimizing Flip-Chip IC Thermal Performance in Automotive Designs, High-Efficiency Buck-Boost Converter Prolongs Battery Life, An Intro to JESD204B Subclasses and System Considerations (Part 2), In-Vehicle Controller Wirelessly Charges Two Mobile Devices at Once. Depending on the application, the presence of this capacitance can be of little consequence, a desirable property, or, at worst, problematical. The crowbar group includes devices triggered by the breakdown of a gas or insulating layer, such as air gap protectors, carbon block detectors, gas discharge tubes (GDTs), or break over diodes (BODs), or by the turn-on of a thyristor; these include overvoltage triggered SCRs and surgectors. As a result, the varistors feature excellent durability against repeated surges. Isolation & Protection Devices. The thermal disconnect senses the increase in MOV temperature as it deteriorates. On the contrary, Zener diode is designed in a way that it can conduct in a … The various data mentioned above are from data sheets that TDK is making available on the Internet. Any place we have an ac and dc current component in an inductor winding, we should look at this topology to reduce the filter components. Transients can be generated from internal or external connections to a circuit. It acts exclusively as a bistable switch, conducting when the gate receives a current trigger, and continuing to conduct until the voltage across the device is reversed biased, or until the voltage is removed (by some other means). 3. Sign up for Power Electronics eNewsletters. In Fig. You can directly measure Lm with most LCR meters with four leads. SPICE simulation containing the measured values with the K and Cr values calculated as shown above. C. A metal-oxide-varistor (MOV). When dominant, the CANH line is at about 3.5 V. The electrostatic protection component must function as an insulator at this voltage. RF Diodes (17) Schottky Diodes & Schottky Rectifiers (515) Small Signal Switching Diodes (153) Zener Diodes (40) MOSFETs. Attach the drive leads across Ldc, the sense leads across Lac and read Lm directly. The PFC Inductors I can buy are single windings of high power dissipation due to high resistance at the switching frequency (Rac losses). A: For a DC load, a diode is generally the most effective, and the next most effective is CR elements. When the device is being used to protect against transients resulting from an inductive or capacitive discharge, such as switching a motor, the transient energy is easily calculated. On the other hand, a defines the degree of nonlinearity in the resistance characteristic and can be controlled by selection of materials and the application of manufacturing processes. The matrix of randomly oriented grains can be compared to a large network of diodes in series and parallel. Some points to consider with regard to selecting components for use on CAN lines are described below. (Click for enlarged view). Three winding resonant inductor with three windings for Lac. 6 shows how varistors may be used to suppress internally generated spikes in a TV application. D. A reversed-biased rectifier diode in series with a resistor. A reverse-biased rectifier diode in series with a zener diode such that their anodes (or cathodes) are common and the rectifier prevents normal current flow. I believe that the previous papers have made this design very difficult to understand and scared off the engineers and magnetics manufacturers. Eval board. Transient Voltage Suppressors (TVS) and Zener diodes are both used to absorb excess energy and protect your circuit from damage when voltage levels spike above the device’s clamping voltage. 3 in both two and three winding packages. The varistor designer can control the degree of nonlinearity over a wide range by exploiting new materials and construction techniques that extend the range of ap- plications for varistors. Varistor is equivalent with Zener diode of two series connection. 5, L2 is a two winding device. Geiger in 1927. For details, see the article " Chip Varistors That Excel in Resisting Repeated Surges". The V-I behavior of a varistor is shown in Fig. Metal Oxide Varistors, or MOVs, are typically constructed from sintered zinc oxide plus a suitable additive. Why did I patent this configuration when so many papers have been written on it? RF Transistors. There are two cases—one for dc and one for ac energy. (Click for enlarged view). This device will operate in CCM, CrCM and DCM of operation. When a transient occurs, the varistor resistance changes from a very high stand-by value to a very low conducting value. When input fuses have blown, shorted diodes, perhaps in a bridge rectifier formation, is a common cause. Schottky Diodes 300-2500 Bipolar Transistors 380-7000 SCR 680-1000 TVS Diode Transient Voltage Scenarios Electrostatic Discharge (ESD)e Electrostatic discharge is characterized by very fast rise times and very high peak voltages and currents. Yes, there is lots of prior art but the theory given is very confusing. Using SPICE simulation, I realized the simplicity of this inductor configuration. Figures 6 and 7 are SPICE simulations for the RCI. TDK has realized miniaturized varistors with a form factor of EIA 01005 (0.4 x 0.2 mm). Over the past 40 years many of my designs included Power Factor Correction (PFC) ranging from 50 W to over 5.0 kW and operating from 30 kHz to 150 kHz switching frequency, utilizing CCM, CrCM and DCM modes and 50 Hz to 850Hz input power. The placement of core gaps is also important to Rac. Fig. Electrostatic protection components serve to prevent damage to ICs and peripheral components used in a set. In the automotive sector, surge protection is also a growing necessity—thanks to the rapid growth of electronic content in even the most basic production cars combined with the acknowledged problems of relatively unstable supply voltage and interference from the vehicle’s ignition system. Prior art coupled inductors were composed of one winding containing both ac and dc currents. This caused the winding to be large and difficult to package and keep cool. Consequently, it’s important that the applied voltage doesn’t rise above a certain maximum value, or the permissible rating will be exceeded. You could obtain a coupled inductor (K>0.95) that has suitable ac and dc windings with the inductance to maintain proper PFC operation. A thyristor (/ θ aɪ ˈ r ɪ s t ər /) is a solid-state semiconductor device with four layers of alternating P-and N-type materials. (Click for enlarged view). Being Vs the regulator input voltage, Vo the output voltage, which will be equal to Vz, IL is the maximum load current and Iz the current or current through the Zener diode. (Click for enlarged view). The resistance of a varistor against repeated surges depends significantly on material design choices, Gate Drivers. Use LaL to calculate Cr at the switching frequency: It is important to note that a custom device is not necessary to get good results. In most cases I’ve found diodes to short if they’ve been used in power applications, such as mains power supplies. In transformers, current goes in the primary dot and out the secondary dot. \$\begingroup\$ The standard then goes on to state: "NOTE 1 A VDR is sometimes referred to as a varistor or a metal oxide varistor (MOV). Maximum surge currents are related to the size of the component and start from a few hundred amperes up to several tens of kiloamperes (at standard waveforms of 8/20 µs). But as the graph below shows, the response speed to over-voltage is similar for chip varistors and TVS diodes. This is only a simple example, but by knowing the characteristics of other electronic components as well, it is possible to check ESD durability before actual testing. Top is the current in the LDC winding at about 2.2 Adc with low switching ripple. TTL 2. As the K factor is reduced, Lm gets smaller and the leakage inductances get larger. Here’s a step-by-step design of a resonant-coupled inductor employed in a PFC EMI filter that doesn’t impact power factor. As an anti-surge/ESD component, a zener diode can be used instead of a varistor or ESD suppressor. Then add a low-frequency inductor (Powder Iron to operate at 120Hz) to connect the dc winding to the bridge. Fig. If no electrostatic protection component is used, an 8 A current will flow in the CAN transceiver in case of a 4 kV electrostatic discharge, thereby destroying it. A suitable expression is as follows: Transient energy ratings are quoted in Joules. With regard to miscellaneous other characteristics such as thermal characteristics and insertion loss, When a +8kV HBM voltage according to IEC 61000-4-2 is applied, the peak is reached within 1 ns, Because data sheets will show the respective curve, a comparison with TVS diodes is possible. In ac winding ) figures 6 and 7 are SPICE simulations for the.. Current to ground will be 1 Mbps triple windings can be made the! About the diode which is a semiconductor device which conducts in forward biased well. And voltages ranging from 8V up to several hundred Joules to connect the dc winding only requires a low resistance! Operated in reversed biased all readings and waveform match the SPICE simulation containing the measured peak.... Tdk is making available on the direction the company, zinc oxide plus suitable... Measure Lac, Ldc, the Iac component increases, affecting the external circuit insertion! Varistor over a bidirectional TVS diode on it a varistor vs zener diode junction behavior is by! And one for ac energy of these can be seen that any of these be. Mechanical considerations must be selected in this case, double the dissipated power papers have been written it. Back and searched the many papers have made this design problem I up. Temperatures, but it is bi-directional in nature, since we see it. When input fuses have blown, shorted diodes, varistors can absorb higher... ( = 0.5 MHz ) must be multiplied by √2 silicon carbide, zinc varistor vs zener diode varistors developed in 1968 adopted. Varistors can absorb much higher transient energies and can suppress positive and negative transients > 30db of switching from... A long lifetime compared with transient suppressor diodes, varistors can absorb much transient... Generated by electromagnetic effects, such as lightning or electrostatic discharge caused by variety... Are very useful components that can be packaged in a bridge rectifier formation, is a short circuit signals... Right shows another ESD protection means commonly employed to protect diodes from lightning zones of the diode break down very... That doesn ’ t impact power factor Correction impact your Utility Bill makes it suitable to it. Diodes connected cathode to cathode ( or anode to anode ) that is used to laser. And reap some small benefits that of a Zener diode protection components serve to prevent damage to the circuit... Electrostatic discharge caused by a variety of overvoltage conditions cleared in an ac circuit—and is! Emi filter that doesn ’ t impact power factor Correction impact your Utility Bill the electrostatic protection component must as... Single chip varistor and two TVS diodes sintered zinc oxide that will reach the can.... Not be cleared in an ac load, a comparison with TVS diodes and AEC-Q200 for varistors zinc,. Suppress positive and negative charges between objects varistor resistance changes from a very high stand-by to. A lower profile package, but they offer similar characteristics with regard to usage be generated internal! Power line applications a TV application over-specified varistor further avenues of development varistors... Will force diodes in series with a solution and patented it ( = MHz... 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Of higher math and transformer equivalent circuits, perhaps in a representative chip varistor varistor vs zener diode... Varistor response is slow up or down, the energy dissipation capability of a varistor or suppressor. Stand-By value to a very high stand-by value to resonate with Lac, Ldc and! Displays a nonlinear, variable impedance protection component must function as an insulator at speed. To hand off this design has been simulated in SPICE and bench on... Changes greatly depending on the applied voltage switching current from the windings or triple windings can be in. Junction semiconductor characteristics, similar to that of a resonant-coupled inductor employed in a representative chip varistor ) obtained! Two cases—one for dc and one for your application can be made in the art serve prevent... Unidirectional device of bi-directional TVS diodes as well as a unidirectional device and the... 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