Surface Mount Varistors

197

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Transient Voltage Surge Suppressor

CH Varistor Series

Power Dissipation Ratings

Continuous power dissipation capability is not an applicable design

requirement for a suppressor, unless transients occur in rapid succession.

Under this condition, 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 specifications shown on the

Device Ratings and Specifications table for the specific device.

Furthermore, the operating values need to be derated at high tempera-

tures 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

FIGURE 2. PEAK PULSE CURRENT TEST WAVEFORM

100

90

50

10

T

TIME

T = Time From 10% to 90% of Peak

Example: For an 8/20µs Current Waveform:

FIGURE 3. CLAMPING VOLTAGE FOR V22CH8 - V68CH8

500

400

300

200

100

90

80

70

60

50

40

30

20

10

PEAK AMPERES (A)

V56CH8

V47CH8

V39CH8

V33CH8

V27CH8

V22CH8

MAXIMUM CLAMPING VOLTAGE

MODEL SIZE 5 x 8mm

V68CH8

FIGURE 4. CLAMPINGVOLTAGE FOR V120CH8 - V430CH8

4,000

3,000

2,000

1,000

900

800

700

600

500

400

300

200

100

V180CH8

V150CH8

V120CH8

V430CH8

V390CH8

V360CH8

V240CH8

V220CH8

V200CH8

PEAK AMPERES (A)

MAXIMUM CLAMPING VOLTAGE

MODEL SIZE 5 x 8mm

Transient V-I Characteristics Curves

Pb

RoHS

3