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Varistor Products
©2009 Littelfuse, Inc.
Revision: November 5, 2009
Specifications are subject to change without notice.
Please refer to www.littelfuse.com for current information.
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 0.3cm.
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 =
1
0
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
V
O
L
T
A
GE (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
(0 TO
)
C
(0.002F)
L
(1)
FIGURE 11. VARISTOR EQUIVALENT CIRCUIT MODEL
Summary :
Electrical Characterization Varistor V-I Characteristics LEAKAGE REGION NORMAL VARISTOR OPERATION UPTURN REGION R = 1 0 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 V O L T A GE (V) FIGURE 10.
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