Varistor Products
Low Profile
RA Varistor Series
Power Dissipation Ratings
Should transients occur in rapid succession, the average power dissipation
required is simply the energy (watt-seconds) per pulse times the number
of pulses per second. The power so developed must be within the specifi-
cations shown on the Device Ratings and Specifications table for the
specific device. Furthermore, the operating values need to be derated
at high temperatures as shown in Figure 1. Because varistors can only
dissipate a relatively small amount of average power they are, therefore,
not suitable for repetitive applications that involve substantial amounts of
average power dissipation.
100
90
80
70
60
50
40
30
20
10
0
-55 50
60
70
80
90 100 110 120 130 140 150
o
AMBIENTTEMPERATURE ( C)
FIGURE 1. CURRENT, ENERGY AND POWER DERATING
CURVE
100
90
50
O = Virtual Origin of Wave
1
T = Time From 10% to 90% of Peak
T = Virtual Front time = 1.25 • t
1
T = Virtual Time to Half Value (Impulse Duration)
2
10
Example: For an 8/20µs Current Waveform:
O
T
TIME
1
8µs = T = Virtual Front Time
1
T
20µs = T = Virtual Time to Half Value
1
2
T
2
FIGURE 2. PEAK PULSE CURRENT TEST WAVEFORM
140
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