© 2014 Littelfuse, Inc.
Specifications are subject to change without notice.
Revised: 05/23/14
Varistor Products
Radial Lead Varistors > LA Series
Should transients occur in rapid succession, the average
power dissipation is the energy (watt-seconds) per pulse
times the number of pulses per second. The power so
developed must be within the specifications shown on the
Device Ratings and Specifications Table for the specific
Current Energy and Power Dissipation Ratings
Peak Pulse Current Test Waveform
FIGURE 2. PEAK PULSE CURRENT TEST WAVEFORM
100
90
50
10
O
1
T
T
1
T
2
TIME
PERCENT OF PEAK VALUE
O
1
= Virtual Origin of Wave
T = Time From 10% to 90% of Peak
T
1
= Virtual Front time = 1.25 • t
T
2
= Virtual Time to Half Value (Impulse Duration)
Example: For an 8/20µs Current Waveform:
8s = T
1
= Virtual Front Time
20 s = T
2
= Virtual Time to Half Value
0
1
= Virtual Origin of Wave
T = Time from 10% to 90% of Peak
T
1
= Rise Time = 1.25 x T
T
2
= Decay Time
Example - For an 8/20 µs Current Waveform:
8µs = T
1
= Rise Time
20µs = T
2
= Decay Time
100
90
80
70
60
50
40
30
20
10
0
-55 50 60 70 80 90 100110 120130 140150
AMBIENT TEMPERATURE (
o
C)
PERCENT OF RATED VALUE
FIGURE 1. CURRENT, ENERGY AND POWER DERATING
CURVE
Figure 1A - Power Derating for Epoxy Coated
Figure 2
FIGURE 1. CURRENT, ENERGY AND POWER DERATING
CURVE
100
90
80
70
60
50
40
30
20
10
0
-55 50 60 70 80 90 100110 120130 140150
AMBIENT TEMPERATURE (
o
C)
PERCENT OF RATED VALUE
device. The operating values of a MOV need to be derated
at high temperatures as shown above. Because varistors
only dissipate a relatively small amount of average power
they are not suitable for repetitive applications that involve
substantial amounts of average power dissipation.
Figure 1B - Power Derating for Phenolic Coated
