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Varistors Catalog
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PRODUCT CATALOG & DESIGN GUIDE

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Metal-Oxide Varistors (MOVs) Littelfuse* Expertise Applied | Answers Delivered Introduction to Overvoltage Suppression Varistor Characteristics, Terms and Consideration Factors Varistor Connection Examples Varistor Selection Worksheet Agency Standards Legal Disclaimers Radial Leaded MOVs: LV UltraMOV® Varistor UltraMOV® Varistor UltraMOV® 25S Varistor C-III LA ZA AUMOV® Varistor HMOV Industrial High Energy Terminal MOVs: BA/BB ^ Radial Leaded Screw / Clip Terminals Industrial Packaged Radial Leads Bare Disc Specialty Application MOVs: MA RA High Reliability rZinc • Oxide Axial Leaded...

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Metal-Oxide Varistors (MOVs) Expertise Applied | Answers Delivered To assure reliable operation, transient voltage suppression should be considered at early stages of the design process. This can be a complex task as electronic components are increasingly sensitive to stray electrical transients. The designer must define the types of transient threats and determine what applications are needed while meeting the product agency norms and standards. Varistors are increasingly used as the front-line solution for transient surge protection. Littelfuse provides expertise to the designer and...

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Expertise Applied | Answers Delivered Introduction to Overvoltage Suppression (continued)Transient Threats - What Are Transients? Voltage transients are defined as short duration surges of electrical energy and are the result of the sudden release of energy that was previously stored, or induced by other means, such as heavy inductive loads or lightning strikes. In electrical or electronic circuits, this energy can be released in a predictable manner via controlled switching actions, or randomly induced into a circuit from external sources. Repeatable transients are frequently caused by the...

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Metal-Oxide Varistors (MOVs) Introduction to Overvoltage Suppression (continued) Transient Voltage Scenarios ESD (Electrostatic Discharge) Electrostatic discharge is characterized by very fast rise times and very high peak voltages and currents. This energy is the result of an imbalance of positive and negative charges between objects. Below are some examples of the voltages which can be generated, depending on the relative humidity (RH): • Walking across a carpet: 35kV @ RH = 20%; 1.5kV @ RH = 65% • Walking across a vinyl floor: 12kV @ RH = 20%; 250V @ RH = 65% • Worker at a bench: kV @ RH...

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Metal-Oxide Varistors (MOVs) Expertise Applied | Answers Delivered Figure 5. Cloud-to-Ground Lightning Strike Figure 5 shows the effect of a cloud-to-ground strike: the transient-generating effect is far greater. Technological Solutions for Transient Threats Because of the various types of transients and applications, it is important to correctly match the suppression solution to the different applications. Littelfuse offers the broadest range of circuit protection technologies to ensure that you get the proper solution for your application. Please consult our online library of Application...

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Metal-Oxide Varistors (MOVs) Varistor Characteristics, Terms and Consideration Factors The varistor body structure consists of a matrix of conductive ZNO grains separated by grain boundaries providing P–N junction semiconductor characteristics. These boundaries are responsible for blocking conduction at low voltages and are the source of the nonlinear electrical conduction at higher voltages. Physical Properties VN × d ≈ ----------------3 An attractive property of the MOV is that the PER VERT charelectrical where, d = average grain size FIGURE 1. TYPICAL VARISTOR V-I CHARACTERISTIC The...

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FIGURE 4. CAPACITANCE-VOLTAGE BEHAVIOR OF VARISTOR RESEMBLES A SEMICONDUCTOR ABRUPT-JUNCTION REVERSED BIASED DIODE FIGURE 3. SCHEMATIC DEPICTION OF THE Nd ~ 2 x 1017/cm3 MICROSTRUCTURE OF A METAL-OXIDE Varistor Characteristics, Terms and Consideration Factors (continued) The bulk of the varistor between contacts is comprised of FIGURE 2. OPTICAL PHOTOMICROGRAPH OF A POLISHED ZnO grains of an ETCHED SECTIONas shown in the schematAND average size "d" OF A VARISTOR ic model of Figure 3. Resistivity of the ZnO is <0.3 Ω–cm. CURRENT varistor at the point on its V-I characteristic where the V...

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FIGURE 4. CAPACITANCE-VOLTAGE BEHAVIOR OF 2 VARISTOR RESEMBLES A δ SEMICONDUCTOR 0 ABRUPT-JUNCTION REVERSED BIASED DIODE 17ENERGY BAND DIAGRAM OF A 3 Nd ~ 2 x 10 /cm FIGURE 5. 0 0.4 0.8 1.2 ZnO-GRAINBOUNDARY-ZnO JUNCTION Varistor 3. SCHEMATIC DEPICTION OF THE and Consideration Factors (continued) FIGURE Characteristics, Terms 75 150 1.5 INTERGRANULAR In addition, the width ofdv BOUNDARY39 depletion layer was calculated 25VRMS 80 (Note) the 12 1.0 Z X = ------ = V ⁄ α I = R X ⁄ α to be about 1000 Angstrom units. Single junction studies di FIGURE 3.Low voltage formulation. OF THE NOTE:...

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Metal-Oxide Varistors (MOVs) Varistor Characteristics, Terms and Consideration Factors (continued) Varistor Construction The process of fabricating a Littelfuse Varistor is illustrated in the ﬂow chart of Figure 7 The starting material may . differ in the composition of the additive oxides, in order to cover the voltage range of product. ZnO ADDITIVE OXIDES (MAINLY BL203) MIXING POWDER PREPARATION POWDER PRESS SINTER FORM CERAMIC BODY MECHANICAL ASSEMBLY Radials are also available with phenolic coatings applied using a wet process. The PA Series package consists of plastic molded around a...

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Metal-Oxide Varistors (MOVs) Varistor Characteristics, Terms and Consideration Factors (continued) n = average number of grain boundaries between electrodes LEAKAGE REGION CURRENT (A) NORMAL VARISTOR OPERATION Equivalent Circuit Model An FIGURE 10.model for the varistor CURVE PLOTTED ON by electrical TYPICAL VARISTOR V-I can be represented L LOG-LOG SCALE the simplified equivalent circuit of Figure 11. C FIGURE 12. EQUIVALENT CIRCUIT AT LOW CURRENTS VR FIGURE 4. CAPACITANCE-VOLTAGE BEHAVIOR OF VARISTOR RESEMBLES A SEMICONDUCTOR ABRUPT-JUNCTION REVERSED BIASED DIODE Nd ~ 2 x 1017/cm3 EV 0 B...

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