4-38

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 specifications

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.

1.

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

Transient V-I Characteristics Curves

FIGURE 3. CLAMPING VOLTAGE FOR V8ZA05 - V68ZA05

FIGURE 4. CLAMPING VOLTAGE FOR V82ZA05 - V330ZA05

100

90

50

10

T

TIME

T = Time From 10% to 90% of Peak

Example: For an 8/20

µs Current Waveform:

8

20

600

500

400

300

200

100

90

80

70

60

50

40

30

20

PEAK AMPERES (A)

MAX CLAMPING VOLTAGE

MODEL SIZE 5mm

10

V68ZA05

V56ZA05

V47ZA05

V39ZA05

V33ZA05

V27ZA05

V22ZA05

V18ZA05

V12ZA05

V8ZA05

2000

1000

500

200

PEAK AMPERES (A)

0.01

0.1

1

10

100

1000

100

0.001

0.0001

V330ZA05

V270ZA05

V240ZA05

V220ZA05

V205ZA05

V180ZA05

V150ZA05

V120ZA05

V10

0ZA05

V82ZA05

MAX CLAMPING VOLTAGE

MODEL SIZE 5mm

ZA Series