Varistor Metal Oxide Varistor Products Page 11 Varistor Metal-Oxide Varistor Products

2017 Littelfuse, Inc. Specifications are subject to change without notice. Revised: 09/14/17 Metal-Oxide Varistors (MOVs) Equivalent Circuit Model An electrical model for the varistor can be represented by the simplified equivalent circuit of Figure 11. Turning now to the high current upturn region in Figure 10, we see that the V-I behavior approaches an ohmic char- acteristic. The limiting resistance value depends upon the electrical conductivity of the body of the semiconducting ZnO grains, which have carrier concentrations in the range of 10 17 to 10 18 per cm 3 . This would put the ZnO resistivity below 0.3 cm. Varistor electrical characteristics are conveniently displayed using log-log format in order to show the wide range of the V-I curve. The log format also is clearer than a linear representation which tends to exaggerate the nonlinearity in proportion to the current scale chosen. A typical V-I characteristic curve is shown in Figure 10. This plot shows a wider range of current than is normally provided on varis- tor data sheets in order to illustrate three distinct regions of electrical operation. Electrical Characterization Varistor V-I Characteristics LEAKAGE REGION NORMAL VARISTOR OPERATION UPTURN REGION R = 10 9 1 --- SLOPE = I = kV R = 1 - 10 10 -8 10 -6 10 -4 10 -2 10 0 10 2 10 4 20 (TYPICAL V130LA20A) CURRENT (A) 50 200 100 500 1000 10 VOLTAGE (V) FIGURE 10. TYPICAL VARISTOR V-I CURVE PLOTTED ON LOG-LOG SCALE DB SERIES DA SERIES BA/BB SERIES FIGURE 9C. PICTORIAL VIEW OF HIGH ENERGY DA, DB AND BA/BB SERIES R ON R OFF (1000M) (TYPICAL V130LA20A) (LEAD INDUCTANCE) V R x (0T ) C (0.002F) L (1) FIGURE 11. VARISTOR EQUIVALENT CIRCUIT MODEL Varistor Characteristics, Terms and Consideration Factors (continued)

Previous Page
Next Page