140

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Varistor Products

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.

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

100

110

120

130

140 150

100

90

50

10

T

TIME

Low Profile

T = Time From 10% to 90% of Peak

Example: For an 8/20µs Current Waveform:

FIGURE 2. PEAK PULSE CURRENT TEST WAVEFORM