3EZ4.3D5 Series

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5

APPLICATION NOTE

Since the actual voltage available from a given zener

diode is temperature dependent, it is necessary to determine

junction temperature under any set of operating conditions

in order to calculate its value. The following procedure is

recommended:

depends on the device mounting method.

30−40°C/W for the various clips and tie points in common

use and for printed circuit board wiring.

The temperature of the lead can also be measured using a

thermocouple placed on the lead as close as possible to the

tie point. The thermal mass connected to the tie point is

normally large enough so that it will not significantly

respond to heat surges generated in the diode as a result of

pulsed operation once steady-state conditions are achieved.

may be determined by:

temperature and may be found from Figure 2 for a train of

power pulses (L = 3/8 inch) or from Figure 10 for dc power.

from Figures 5 and 6.

Under high power-pulse operation, the zener voltage will

vary with time and may also be affected significantly by the

zener resistance. For best regulation, keep current

excursions as low as possible.

Data of Figure 2 should not be used to compute surge

capability. Surge limitations are given in Figure 3. They are

lower than would be expected by considering only junction

temperature, as current crowding effects cause temperatures

to be extremely high in small spots resulting in device

degradation should the limits of Figure 3 be exceeded.